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UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of
the Securities Exchange Act of 1934 (Amendment No.          )

 

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AVISTA HEALTHCARE PUBLIC ACQUISITION CORP.
65 EAST 55TH STREET, 18TH FLOOR
NEW YORK, NEW YORK 10022
NOTICE OF EXTRAORDINARY GENERAL MEETING

TO BE HELD [    ·    ], 2018

TO THE SHAREHOLDERS OF AVISTA HEALTHCARE PUBLIC ACQUISITION CORP.:

        You are cordially invited to attend the extraordinary general meeting (the "extraordinary general meeting") of Avista Healthcare Public Acquisition Corp., a Cayman Islands exempted company ("AHPAC," the "Company," "we," "us" or "our"), on [    ·    ] at [    ·    ] Eastern Time at the offices of Weil, Gotshal & Manges LLP, located at 767 Fifth Avenue, New York, NY 10153, for the sole purpose of considering and voting upon (i) a proposal to amend the Company's amended and restated memorandum and articles of association (the "Articles") to extend the date by which the Company has to consummate a business combination (the "Extension") from October 14, 2018 to February 15, 2019 (the "Extended Date") (the "Extension Amendment Proposal"), (ii) a proposal to amend the Company's Investment Management Trust Agreement (the "Trust Agreement"), dated as of October 10, 2016, by and between AHPAC and Continental Stock Transfer & Trust Company (the "trustee"), to extend the date on which to commence liquidating the trust account ("trust account") established in connection with the Company's initial public offering ("IPO") in the event the Company has not consummated a business combination prior to October 14, 2018 from October 14, 2018 to the Extended Date (the "Trust Amendment Proposal") and (iii) a proposal to adjourn the extraordinary general meeting to a later date or dates, if necessary, to permit further solicitation and vote of proxies if, based upon the tabulated vote at the time of the extraordinary general meeting, there are not sufficient votes to approve the Extension Amendment Proposal and the Trust Amendment Proposal (the "Adjournment Proposal").

        Each of the Extension Amendment Proposal, the Trust Amendment Proposal and the Adjournment Proposal are more fully described in the accompanying proxy statement.

        The purpose of the Extension Amendment Proposal, the Trust Amendment Proposal and, if necessary, the Adjournment Proposal, is to allow the Company more time to complete its proposed business combination (the "Organogenesis Transaction") pursuant to that certain Agreement and Plan of Merger, dated as of August 17, 2018 (as it may be amended, the "Merger Agreement"), by and among the Company, Avista Healthcare Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of the Company ("Merger Sub") and Organogenesis Inc., a Delaware corporation ("Organogenesis"). Our IPO prospectus and our Articles provide that the Company has until October 14, 2018 to complete its initial business combination (the "Termination Date"). Our board of directors has determined that it is in the best interests of our shareholders to extend the Termination Date by approving the Extension Amendment Proposal and the Trust Amendment Proposal to allow additional time to consummate the Organogenesis Transaction. While we have entered into the Merger Agreement with Merger Sub and Organogenesis and intend to file with the Securities and Exchange Commission a registration statement on Form S-4 including the joint proxy/consent solicitation statement/prospectus forming a part thereof (the "Registration Statement") in respect of the Organogenesis Transaction promptly, our board currently believes that there may not be sufficient time before the Termination Date to hold an extraordinary general meeting at which to conduct a vote for shareholder approval of the Organogenesis Transaction and consummate the closing of the Organogenesis Transaction. Accordingly, our board of directors believes that in order to be able to consummate the Organogenesis Transaction, we will need to obtain the Extension.

        As previously reported, on August 21, 2017, the Company entered into a transaction agreement by and among the Company, Merger Sub, Avista Healthcare NewCo, LLC, a Delaware limited liability company and a direct wholly-owned subsidiary of the Company ("NewCo"), Envigo International Holdings, Inc., a Delaware corporation ("Envigo") and Jermyn Street Associates, LLC, solely in its capacity as Shareholder Representative (as defined therein), as amended by that certain Amendment No. 1, dated as of November 22, 2017, as further amended by that certain Amendment No. 2, dated as

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of December 22, 2017, as further amended by that certain Amendment No. 3, dated as of January 21, 2018 and as further amended by that certain Amendment No. 4, dated as of February 9, 2018 (the "Transaction Agreement"). On February 14, 2018, pursuant to Section 7.1(a) of the Transaction Agreement, the Company and Envigo entered into a Mutual Termination Agreement (the "Mutual Termination Agreement") and the Transaction Agreement was terminated effective as of February 14, 2018.

        The holders of AHPAC's Class A ordinary shares issued in the Company's IPO (the "public shares") who vote either for or against the Extension Amendment Proposal may elect to redeem their public shares in exchange for their pro rata portion of the funds held in the trust account established at the time of the IPO (the "trust account") if the Extension is implemented (the "Redemption"). For illustrative purposes, based on the fair market value of marketable securities held in the trust account of approximately $315,299,762 as of August 15, 2018, the estimated per share redemption price would have been approximately $10.17. The Company estimates that the per share pro rata portion of the trust account will be approximately $[    ·    ] at the time of the extraordinary general meeting. The closing price of the public shares on [    ·    ], 2018 was $[    ·    ]. Accordingly, if the market price were to remain the same until the date of the extraordinary general meeting, exercising redemption rights would result in a public shareholder receiving approximately $[    ·    ] more[/less] than if the stock was sold in the open market. The Company cannot assure shareholders that they will be able to sell their public shares in the open market, even if the market price per share is higher than the redemption price stated above, as there may not be sufficient liquidity in its securities when such shareholders wish to sell their shares. The Company believes that such redemption right enables the Company's public shareholders to determine not to sustain their investments for an additional period if the Company does not complete the Organogenesis Transaction in the timeframe contemplated by the terms of its Articles. If the Extension Amendment Proposal and Trust Amendment Proposal are approved by the requisite vote of shareholders, the remaining holders of public shares will retain their right to convert their public shares for their pro rata portion of the funds available in the trust account when the Organogenesis Transaction is submitted to shareholders for approval and adoption.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are not approved, and the Organogenesis Transaction is not completed before October 14, 2018, as contemplated by our IPO prospectus and in accordance with our Articles, we will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem 100% of the issued and outstanding public shares with the aggregate amount then on deposit in the trust account and (iii) thereafter seek to dissolve and liquidate as described in more detail in this proxy statement.

        A special resolution, being the affirmative vote of holders of at least two-thirds of the public shares and the Company's Class B ordinary shares, par value $0.0001 per share (the "Class B ordinary shares" and, together with the public shares, the "Ordinary Shares") represented in person or by proxy and entitled to vote thereon at the extraordinary general meeting (voting together as a single class) will be required to approve the Extension Amendment Proposal. The affirmative vote of holders of sixty five percent (65%) of the issued and outstanding Ordinary Shares will be required to approve the Trust Amendment Proposal.

        The approval of both the Extension Amendment Proposal and the Trust Amendment Proposal are essential to the implementation of our board's plan to extend the date by which we must consummate our initial business combination. Therefore, our board will abandon and not implement either amendment unless our shareholders approve both the Extension Amendment Proposal and the Trust Amendment Proposal. This means that if one proposal is approved by the shareholders and the other proposal is not, neither proposal will take effect. Notwithstanding shareholder approval of the Extension Amendment Proposal and the Trust Amendment Proposal, our board will retain the right to abandon and not implement the Extension Amendment Proposal and the Trust Amendment Proposal at any time without any further action by our shareholders.

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        Approval of the Adjournment Proposal requires the affirmative vote of holders of a majority of the Ordinary Shares represented in person or by proxy at the extraordinary general meeting. The Adjournment Proposal will only be put forth for a vote if the Extension Amendment Proposal and Trust Amendment Proposal are not approved at the extraordinary general meeting.

        The Company's board of directors has fixed the close of business on [    ·    ], 2018 (the "Record Date") as the date for determining the Company's shareholders entitled to receive notice of and vote at the extraordinary general meeting and any adjournment thereof. Only holders of record of Ordinary Shares on that date are entitled to have their votes counted at the extraordinary general meeting or any adjournment thereof.

        After careful consideration of all relevant factors, the Company's board of directors has determined that the Extension Amendment Proposal, the Trust Amendment Proposal and the Adjournment Proposal are fair to and in the best interests of the Company and its shareholders, has declared it advisable and recommends that you vote or give instruction to vote "FOR" such proposals.

        Enclosed is the proxy statement containing detailed information concerning the Extension Amendment Proposal, the Trust Amendment Proposal, the Adjournment Proposal and the extraordinary general meeting. Whether or not you plan to attend the extraordinary general meeting, we urge you to read this material carefully and vote your shares.

        I look forward to seeing you at the extraordinary general meeting.

Your vote is very important. Whether or not you plan to attend the extraordinary general meeting, please vote as soon as possible by following the instructions in this proxy statement to make sure that your shares are represented at the extraordinary general meeting. The approval of the Extension Amendment Proposal requires a special resolution, being the affirmative vote of holders of at least two-thirds of the Ordinary Shares represented in person or by proxy and entitled to vote thereon at the extraordinary general meeting. Accordingly, if you fail to vote by proxy or to vote in person at the extraordinary general meeting, your shares will not be counted in connection with the determination of whether a valid quorum is established, however, if a valid quorum is otherwise established, such failure to vote will have no effect on the outcome of any vote on the Extension Amendment Proposal. The approval of the Trust Amendment Proposal requires the affirmative vote of holders of sixty five percent (65%) of the issued and outstanding Ordinary Shares. Accordingly, if you fail to vote by proxy or to vote in person at the extraordinary general meeting, such failure to vote will affect the outcome of any vote on the Trust Amendment Proposal as it will be the equivalent of a vote against the Trust Amendment Proposal. Approval of the Adjournment Proposal will require the affirmative vote of the majority of the Ordinary Shares represented in person or by proxy and entitled to vote thereon at the extraordinary general meeting. Accordingly, if you fail to vote by proxy or to vote in person at the extraordinary general meeting, your shares will not be counted in connection with the determination of whether a valid quorum is established, however, if a valid quorum is otherwise established, such failure to vote will have no effect on the outcome of any vote on the Adjournment Proposal. If you hold your shares in "street name" through a bank, broker or other nominee, you will need to follow the instructions provided to you by your bank, broker or other nominee to ensure that your shares are represented and voted at the extraordinary general meeting.

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AVISTA HEALTHCARE PUBLIC ACQUISITION CORP.
65 EAST 55TH STREET, 18TH FLOOR
NEW YORK, NEW YORK 10022

NOTICE OF EXTRAORDINARY GENERAL MEETING

TO BE HELD [    ·    ], 2018

PROXY STATEMENT

        Avista Healthcare Public Acquisition Corp., a Cayman Island exempted company ("AHPAC," the "Company," "we," "us" or "our"), is providing this proxy statement in connection with the solicitation by the Board of proxies to be voted at the Extraordinary General Meeting to be held on [    ·    ], 2018, at [    ·    ] Eastern Time at the offices of Weil, Gotshal & Manges LLP, located at 767 Fifth Avenue, New York, NY 10153 (the "extraordinary general meeting").

        At the extraordinary general meeting, proposals (i) to amend the Company's amended and restated articles of association (the "Articles") to extend the date by which the Company has to consummate a business combination (the "Extension") from October 14, 2018 to February 15, 2019 (the "Extended Date") (the "Extension Amendment Proposal"), (ii) to amend the Company's Investment Management Trust Agreement (the "Trust Agreement"), dated as of October 10, 2016, by and between AHPAC and Continental Stock Transfer & Trust Company (the "trustee"), to extend the date on which to commence liquidating the trust account ("trust account") established in connection with the Company's initial public offering ("IPO") in the event the Company has not consummated a business combination prior to October 14, 2018 from October 14, 2018 to the Extended Date (the "Trust Amendment Proposal") and (iii) a proposal to adjourn the extraordinary general meeting to a later date or dates, if necessary, to permit further solicitation and vote of proxies if, based upon the tabulated vote at the time of the extraordinary general meeting, there are not sufficient votes to approve the Extension Amendment Proposal and the Trust Amendment Proposal (the "Adjournment Proposal"), will be considered and voted upon.

        The purpose of the Extension Amendment Proposal, the Trust Amendment Proposal and, if necessary, the Adjournment Proposal, is to allow the Company more time to complete its proposed business combination (the "Organogenesis Transaction") pursuant to that certain Agreement and Plan of Merger, dated as of August 17, 2018 (as it may be amended, the "Merger Agreement"), by and among the Company, Avista Healthcare Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of the Company ("Merger Sub") and Organogenesis Inc., a Delaware corporation ("Organogenesis") which contemplates the domestication of AHPAC as a Delaware corporation in accordance with Section 388 of the Delaware General Corporation Law and the Cayman Islands Companies Law (2018 Revision) (the "domestication"), the merger of Merger Sub with and into Organogenesis, with Organogenesis surviving the merger as a wholly owned direct subsidiary of AHPAC (the "merger") and the other transactions contemplated by the Merger Agreement. Our IPO prospectus and our Articles provide that the Company has until October 14, 2018 to complete its initial business combination (the "Termination Date"). Our board of directors has determined that it is in the best interests of our shareholders to extend the Termination Date by approving the Extension Amendment Proposal and the Trust Amendment Proposal. While we have entered into the Merger Agreement with Merger Sub and Organogenesis and intend to file with the Securities and Exchange Commission a registration statement on Form S-4 including the joint proxy/consent solicitation statement/prospectus forming a part thereof (the "Registration Statement") in respect of the Organogenesis Transaction promptly, our board currently believes that there may not be sufficient time before the Termination Date to hold an extraordinary general meeting at which to conduct a vote for shareholder approval of the Organogenesis Transaction and consummate the closing of the

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Organogenesis Transaction. Accordingly, our board of directors believes that in order to be able to consummate the Organogenesis Transaction, we will need to obtain the Extension.

        As previously reported, on August 21, 2017, the Company entered into a transaction agreement by and among the Company, Merger Sub, Avista Healthcare NewCo, LLC, a Delaware limited liability company and a direct wholly owned subsidiary of the Company ("NewCo"), Envigo International Holdings, Inc., a Delaware corporation ("Envigo") and Jermyn Street Associates, LLC, solely in its capacity as Shareholder Representative (as defined therein), as amended by that certain Amendment No. 1, dated as of November 22, 2017, as further amended by that certain Amendment No. 2, dated as of December 22, 2017, as further amended by that certain Amendment No. 3, dated as of January 21, 2018 and as further amended by that certain Amendment No. 4, dated as of February 9, 2018 (the "Transaction Agreement"). On February 14, 2018, pursuant to Section 7.1(a) of the Transaction Agreement, the Company and Envigo entered into a Mutual Termination Agreement (the "Mutual Termination Agreement") and the Transaction Agreement was terminated effective as of February 14, 2018.

        The holders of AHPAC's Class A ordinary shares issued in the Company's IPO (the "public shares") who vote either for or against the Extension Amendment Proposal may elect to redeem their public shares in exchange for their pro rata portion of the funds held in the trust account established at the time of the IPO (the "trust account") if the Extension is implemented (the "Redemption"). For illustrative purposes, based on the fair market value of marketable securities held in the trust account of approximately $315,299,762 as of August 15, 2018, the estimated per share redemption price would have been approximately $10.17. The Company estimates that the per share pro rata portion of the trust account will be approximately $[    ·    ] at the time of the extraordinary general meeting. The closing price of the public shares on [    ·    ], 2018 was $[    ·    ]. Accordingly, if the market price were to remain the same until the date of the extraordinary general meeting, exercising redemption rights would result in a public shareholder receiving approximately $[    ·    ] more[/less] than if he sold his stock in the open market. The Company cannot assure shareholders that they will be able to sell their public shares in the open market, even if the market price per share is higher than the redemption price state above, as there may not be sufficient liquidity in its securities when such shareholders wish to sell their shares. The Company believes that such redemption right enables the Company's public shareholders to determine not to sustain their investments for an additional period if the Company does not complete the Organogenesis Transaction in the timeframe contemplated by the terms of its Articles. If the Extension Amendment Proposal and Trust Amendment Proposal are approved by the requisite vote of shareholders, the remaining holders of public shares will retain their right to convert their public shares for their pro rata portion of the funds available in the trust account when the Organogenesis Transaction is submitted to shareholders.

        Approval of the Extension Amendment Proposal and the Trust Amendment Proposal are conditions to the implementation of the Extension.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, the amount remaining in the trust account may be only a small fraction of the approximately $[    ·    ] million that was in the trust account as of [    ·    ], 2018 (the "Record Date") following the Redemption. Concurrently with the signing of the Merger Agreement, AHPAC entered into a subscription agreement with Avista Capital Partners IV, L.P., a Delaware limited partnership and Avista Capital Partners IV (Offshore), L.P., a limited partnership formed under the laws of Bermuda (collectively, the "PIPE Investor") for the purchase and sale of 9,022,741 shares of Class A Common Stock of AHPAC after the domestication and 4,100,000 warrants to purchase one-half of one share of Class A Common Stock of AHPAC after the domestication, for an aggregate purchase price of $46,000,000, immediately following the domestication, through a private placement offered to a limited number of accredited investors (as defined by Rule 501 of Regulation D) pursuant to Section 4(a)(2) of the Securities Act of 1933, as amended (the "private placement"). Due to the private placement, the

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Company believes there will be sufficient funds available to complete the Organogenesis Transaction, if all other conditions to the consummation of the Organogenesis Transaction are satisfied.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are not approved at the extraordinary general meeting or at any adjournment thereof, and the Organogenesis Transaction is not completed before October 14, 2018, as contemplated by our IPO prospectus and in accordance with our Articles, we will: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem the public shares, at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the trust account, including interest (which interest shall be net of taxes payable, and less up to $50,000 of interest to pay dissolution expenses) divided by the number of then issued and outstanding public shares, which redemption will completely extinguish public shareholders' rights as shareholders (including the right to receive further liquidation distributions, if any), subject to applicable law, and (iii) as promptly as reasonably possible following such redemption, subject to the approval of our remaining shareholders and our Board of Directors, dissolve and liquidate, subject in each case to our obligations under Cayman Islands law to provide for claims of creditors and the requirements of other applicable law.

        The Company's shareholders prior to the IPO (the "initial shareholders") have waived their rights to participate in any liquidation distribution with respect to the 7,750,000 shares acquired by them prior to the IPO ("founder shares"). As a consequence of such waivers, a liquidating distribution will be made only with respect to the public shares. There will be no distribution from the trust account with respect to the Company's warrants, which will expire worthless in the event the Company dissolves and liquidates the trust account.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, the Company will (i) remove from the trust account an amount (the "Withdrawal Amount") equal to the pro rata portion of funds available in the trust account relating to the redeemed public shares and (ii) deliver to the holders of such redeemed public shares their pro rata portion of the Withdrawal Amount. The remainder of such funds shall remain in the trust account and be available for use by the Company to complete the Organogenesis Transaction on or before the Extended Date. The remaining holders of public shares will retain their right to convert their public shares for their pro rata portion of the funds available in the trust account when the Organogenesis Transaction is submitted to shareholders.

        Record holders of Ordinary Shares at the close of business on the Record Date are entitled to vote or have their votes cast at the extraordinary general meeting. On the Record Date, there were [    ·    ] issued and outstanding Ordinary Shares, including [    ·    ] issued and outstanding public shares. The Company's warrants do not have voting rights.

        This proxy statement contains important information about the extraordinary general meeting and the Extension Amendment Proposal, the Trust Amendment Proposal and the Adjournment Proposal. Please read it carefully and vote your shares.

        This proxy statement is dated [    ·    ], 2018 and is first being mailed to shareholders on or about that date.

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QUESTIONS AND ANSWERS ABOUT THE EXTRAORDINARY GENERAL MEETING

        These Questions and Answers are only summaries of the matters they discuss. They do not contain all of the information that may be important to you. You should read carefully the entire document, including the annexes to this proxy statement.

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THE EXTENSION AMENDMENT PROPOSAL

The Extension Amendment Proposal

        The Company is proposing to amend its Articles to extend the date by which the Company has to consummate a business combination to the Extended Date so as to give the Company more time to complete an initial business combination. A copy of the proposed amendment to the Articles of the Company is attached to the proxy statement as Annex A.

        The Organogenesis Transaction qualifies as a "business combination" under the Company's Articles, but the Company believes that there may not be sufficient time before the Termination Date to hold an extraordinary general meeting at which to conduct a vote for shareholder approval of the Organogenesis Transaction and consummate the closing of the Organogenesis Transaction. Accordingly, our board of directors believes that in order to be able to consummate the Organogenesis Transaction, we will need to obtain the Extension. The Company believes that given the Company's expenditure of time, effort and money on the Organogenesis Transaction, circumstances warrant providing public shareholders an opportunity to consider the Organogenesis Transaction.

        All holders of the Company's public shares, whether they vote for or against the Extension Amendment Proposal, are entitled to redeem all or a portion of their public shares in exchange for their pro rata portion of the trust account, provided that the Extension is implemented. For illustrative purposes, based on the fair market value of marketable securities held in the trust account of approximately $315,299,762 as of August 15, 2018, the estimated per share redemption price would have been approximately $10.17. The Company estimates that the per share pro rata portion of the trust account will be approximately $[    ·    ] at the time of the extraordinary general meeting. The closing price of the public shares on [    ·    ], 2018 was $[    ·    ]. Accordingly, if the market price were to remain the same until the date of the extraordinary general meeting, exercising redemption rights would result in a public shareholder receiving approximately $[    ·    ] more[/less] than if he sold his stock in the open market. The Company cannot assure shareholders that they will be able to sell their public shares in the open market, even if the market price per share is higher than the redemption price stated above, as there may not be sufficient liquidity in its securities when such shareholders wish to sell their shares. The Company believes that such redemption right enables the Company's public shareholders to determine not to sustain their investments for an additional period if the Company does not complete the Organogenesis Transaction in the timeframe contemplated by the terms of its Articles. If the Extension Amendment Proposal and Trust Amendment Proposal are approved by the requisite vote of shareholders, the remaining holders of public shares will retain their right to convert their public shares for their pro rata portion of the funds available in the trust account when the Organogenesis Transaction is submitted to shareholders.

Reasons for the Extension Amendment Proposal

        The Company's IPO prospectus and Articles provide that the Company has until October 14, 2018 to complete a business combination. The Company and its officers and directors agreed that it would not seek to amend the Company's Articles to allow for a longer period of time to complete a business combination unless it provided dissenting holders of public shares with the right to seek redemption of their public shares in connection therewith. Because the Company has determined in its reasonable judgment that it may not be able to complete the Organogenesis Transaction, or any other initial business combination, by October 14, 2018, the Company has determined to seek shareholder approval to extend the time for closing a business combination beyond October 14, 2018 to the Extended Date.

        The Extension Amendment Proposal is essential to allowing the Company more time to obtain approval for the Organogenesis Transaction at an extraordinary general meeting and to consummate the closing of the Organogenesis Transaction prior to the Extended Date. Approval of the Extension

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Amendment Proposal and the Trust Amendment Proposal are conditions to the implementation of the Extension.

If the Extension Amendment Proposal Is Not Approved

        If the Extension Amendment Proposal is not approved, we will, unless we complete the Organogenesis Transaction, or another business combination, prior to October 14, 2018: (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem the public shares, at a per-share price, payable in cash, equal to the aggregate amount then on deposit in the trust account, including interest (which interest shall be net of taxes payable, and less up to $50,000 of interest to pay dissolution expenses) divided by the number of then issued and outstanding public shares, which redemption will completely extinguish public shareholders' rights as shareholders (including the right to receive further liquidation distributions, if any), subject to applicable law, and (iii) as promptly as reasonably possible following such redemption, subject to the approval of our remaining shareholders and our Board of Directors, dissolve and liquidate, subject in each case to our obligations under Cayman Islands law to provide for claims of creditors and the requirements of other applicable law.

        The Company's initial shareholders have waived their rights to participate in any liquidation distribution with respect to their founder shares. There will be no distribution from the trust account with respect to the Company's warrants which will expire worthless in the event the Company dissolves and liquidates the trust account. The Company will pay the costs of liquidation from its remaining assets outside of the trust account.

If the Extension Amendment Proposal is Approved

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, the Company will file an amendment to the Articles with the Cayman Islands in the form of Annex A hereto to extend the time it has to complete a business combination until the Extended Date. The Company will then continue to attempt to consummate a business combination until the Extended Date. The Company will remain a reporting company under the Securities Exchange Act of 1934 and its units, common stock and warrants will remain publicly traded during this time. The terms of the warrants will continue in accordance with their terms, with the warrants becoming exercisable upon the consummation of any business combination on or prior to the Extended Date.

        You are not being asked to vote on any business combination at this time. If the Extension is implemented and you do not elect to redeem your public shares, you will retain the right to vote on the Organogenesis Transaction, or any other proposed business combination, when and if it is submitted to shareholders and the right to redeem your public shares into a pro rata portion of the trust account in the event the Organogenesis Transaction or any other business combination is approved and completed or the Company has not consummated a business combination by the Extended Date.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, and the Extension is implemented, the removal of the Withdrawal Amount from the trust account will reduce the Company's net asset value. The Company cannot predict the amount that will remain in the trust account if the Extension Amendment Proposal is approved, and the amount remaining in the trust account may be only a small fraction of the approximately $[    ·    ] million that was in the trust account as of the Record Date.

Redemption Rights

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, and the Extension is implemented, each public shareholder may seek to redeem his public shares for a pro rata portion of the funds available in the trust account, less any income taxes owed on such funds but not

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yet paid. If you exercise your redemption rights, you will be exchanging your public shares for cash and will no longer own the shares.

        TO DEMAND REDEMPTION, YOU MUST CHECK THE BOX ON THE PROXY CARD PROVIDED FOR THAT PURPOSE AND RETURN THE PROXY CARD IN ACCORDANCE WITH THE INSTRUCTIONS PROVIDED, SUBMIT A REQUEST IN WRITING THAT WE REDEEM YOUR PUBLIC SHARES FOR CASH TO CONTINENTAL STOCK TRANSFER & TRUST COMPANY AT THE ADDRESS BELOW, AND, AT THE SAME TIME, ENSURE YOUR BANK OR BROKER COMPLIES WITH THE REQUIREMENTS IDENTIFIED ELSEWHERE HEREIN, INCLUDING DELIVERING YOUR SHARES TO THE TRANSFER AGENT PRIOR TO THE VOTE ON THE EXTENSION AMENDMENT AND THE TRUST AMENDMENT.

        In connection with tendering your shares for redemption, prior to 5:00 PM Eastern time on [    ·    ], 2018 (two business days before the extraordinary general meeting), you must elect either to physically tender your stock certificates to the Transfer Agent, at Continental Stock Transfer & Trust Company, 1 State Street—30th Floor, New York, New York 10004, Attn: Mark Zimkind, mzimkind@continentalstock.com, or to deliver your shares to the transfer agent electronically using DTC's DWAC system, which election would likely be determined based on the manner in which you hold your shares. The requirement for physical or electronic delivery prior to 5:00 PM Eastern time on [    ·    ], 2018 (two business days before the extraordinary general meeting) ensures that a redeeming holder's election is irrevocable once the Extension Amendment Proposal and the Trust Amendment Proposal are approved. In furtherance of such irrevocable election, shareholders making the election will not be able to tender their shares after the vote at the extraordinary general meeting.

        The electronic delivery process through the DWAC system can be accomplished by the shareholder, whether or not it is a record holder or its shares are held in "street name," by contacting the Transfer Agent or its broker and requesting delivery of its shares through the DWAC system. Delivering shares physically may take significantly longer. In order to obtain a physical stock certificate, a shareholder's broker and/or clearing broker, DTC, and the Transfer Agent will need to act together to facilitate this request. There is a nominal cost associated with the above-referenced tendering process and the act of certificating the shares or delivering them through the DWAC system. The transfer agent will typically charge the tendering broker $45 and the broker would determine whether or not to pass this cost on to the redeeming holder. It is the Company's understanding that shareholders should generally allot at least two weeks to obtain physical certificates from the transfer agent. The Company does not have any control over this process or over the brokers or DTC, and it may take longer than two weeks to obtain a physical stock certificate. Such shareholders will have less time to make their investment decision than those shareholders that deliver their shares through the DWAC system. Shareholders who request physical stock certificates and wish to redeem may be unable to meet the deadline for tendering their shares before exercising their redemption rights and thus will be unable to redeem their shares.

        Certificates that have not been tendered in accordance with these procedures prior to the vote for the Extension Amendment Proposal will not be redeemed into a pro rata portion of the funds held in the trust account. In the event that a public shareholder tenders its shares and decides prior to the vote at the extraordinary general meeting that it does not want to redeem its shares, the shareholder may withdraw the tender. If you delivered your shares for redemption to our transfer agent and decide prior to the vote at the extraordinary general meeting not to redeem your shares, you may request that our transfer agent return the shares (physically or electronically). You may make such request by contacting our transfer agent at address listed above. In the event that a public shareholder tenders shares and the Extension Amendment Proposal is not approved or is abandoned, these shares will be redeemed in accordance with the terms of the Articles promptly following the extraordinary general meeting as described elsewhere herein. The Company anticipates that a public shareholder who tenders shares for redemption in connection with the vote to approve the Extension Amendment Proposal would receive

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payment of the redemption price for such shares soon after the completion of the Extension Amendment Proposal. The transfer agent will hold the certificates of public shareholders that make the election until such shares are redeemed for cash or returned to such shareholders.

        If properly demanded, the Company will redeem each public share for a pro rata portion of the funds available in the trust account, less any income taxes owed on such funds but not yet paid, calculated as of two days prior to the filing of the amendment to the Articles. As of the Record Date, this would amount to approximately $[    ·    ] per share. The closing price of the public shares on [    ·    ], 2018 was $[    ·    ]. Accordingly, if the market price were to remain the same until the date of the extraordinary general meeting, exercising redemption rights would result in a public shareholder receiving approximately $[    ·    ] more[less] than if he sold his stock in the open market.

Required Vote

        The approval of Extension Amendment Proposal requires the affirmative vote of holders of two-thirds of the Ordinary Shares represented in person or by proxy and entitled to vote thereon at the extraordinary general meeting. All of the Company's directors, executive officers and their affiliates are expected to vote any Ordinary Shares owned by them in favor of the Extension Amendment Proposal. On the Record Date, directors and executive officers of the Company and their affiliates beneficially owned and were entitled to vote [    ·    ] founder shares representing approximately [    ·    ]% of the Company's issued and outstanding Ordinary Shares.

        In addition, the Company's directors, executive officers and their affiliates may choose to buy Ordinary Shares in the open market and/or through negotiated private purchases. In the event that purchases do occur, the purchasers may seek to purchase shares from shareholders who would otherwise have voted against the Extension Amendment Proposal and elected to redeem their shares into a portion of the trust account. Any Ordinary Shares purchased by affiliates will be voted in favor of the Extension Amendment Proposal.

Recommendation of the Board

OUR BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT OUR SHAREHOLDERS VOTE "FOR" THE APPROVAL OF THE EXTENSION
AMENDMENT PROPOSAL

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THE TRUST AMENDMENT PROPOSAL

The Trust Amendment Proposal

        The Trust Amendment Proposal would amend our existing Trust Agreement to change the date by which the trustee must commence liquidating the trust, from the 24-month anniversary of the closing of the IPO to the Extended Date, and make any other conforming amendments. The complete text of the proposed amendment is attached to this proxy statement as Annex B. All shareholders are encouraged to read the proposed amendment in its entirety for a more complete description of its terms.

Reasons for the Trust Amendment Proposal

        The Company's IPO prospectus and Articles provide that the Company has until October 14, 2018 to complete a business combination. The Company and its officers and directors agreed that it would not seek to amend the Company's Articles to allow for a longer period of time to complete a business combination unless it provided dissenting holders of public shares with the right to seek redemption of their public shares in connection therewith. Because the Company has determined in its reasonable judgment that it may not be able to complete the Organogenesis Transaction, or any other initial business combination, by October 14, 2018, the Company has determined to seek shareholder approval to extend the time for closing a business combination beyond October 14, 2018 to the Extended Date.

        The Company is proposing to amend its Trust Agreement to extend the date on which the Trustee must commence liquidating the trust account in the event the Company has not consummated a business combination from October 14, 2018 to the Extended Date.

        The Trust Amendment Proposal is essential to allowing the Company more time to obtain approval for the Organogenesis Transaction at an extraordinary general meeting and consummate the closing of the Organogenesis Transaction prior to the Extended Date. Approval of the Trust Amendment Proposal is a condition to the implementation of the Extension. Approval of the Extension Amendment Proposal and the Trust Amendment Proposal are conditions to the implementation of the Extension.

        If the Trust Amendment Proposal is not approved and we have not consummated the Organogenesis Transaction, or another business combination, by October 14, 2018, we will (i) cease all operations except for the purpose of winding up, (ii) as promptly as reasonably possible but not more than ten business days thereafter, redeem 100% of the issued and outstanding public shares with the aggregate amount then on deposit in the trust account and (iii) thereafter seek to dissolve and liquidate as described in more detail in this proxy statement. There will be no distribution from the trust account with respect to our warrants which will expire worthless in the event we wind up.

Required Vote

        Approval of the amendment to the Trust Agreement requires the affirmative vote of holders of sixty five percent (65%) of the issued and outstanding Ordinary Shares. All of the Company's directors, executive officers and their affiliates are expected to vote any Ordinary Shares owned by them in favor of the Trust Amendment Proposal. On the Record Date, directors and executive officers of the Company and their affiliates beneficially owned and were entitled to vote [    ·    ] founder shares representing approximately [    ·    ]% of the issued and outstanding Ordinary Shares.

        In addition, the Company's directors, executive officers and their affiliates may choose to buy Ordinary Shares in the open market and/or through negotiated private purchases. In the event that purchases do occur, the purchasers may seek to purchase shares from shareholders who would otherwise have voted against the Trust Amendment Proposal and elected to redeem their shares into a portion of the trust account. Any Ordinary Shares purchased by affiliates prior to the Record Date will be voted in favor of the Trust Amendment Proposal.

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Recommendation of the Board

OUR BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT OUR SHAREHOLDERS VOTE "FOR" THE APPROVAL OF THE TRUST AMENDMENT PROPOSAL

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THE ADJOURNMENT PROPOSAL

The Adjournment Proposal

        The Adjournment Proposal, if adopted, will allow our board of directors to adjourn the extraordinary general meeting to a later date or dates to permit further solicitation of proxies. The Adjournment Proposal will only be presented to our shareholders in the event, based on the tabulated votes, there are not sufficient votes at the time of the extraordinary general meeting to approve the Extension Amendment Proposal and the Trust Amendment Proposal.

Consequences if the Adjournment Proposal is Not Approved

        If the Adjournment Proposal is not approved by our shareholders, our board of directors may not be able to adjourn the extraordinary general meeting to a later date in the event, based on the tabulated votes, there are not sufficient votes at the time of the extraordinary general meeting to approve the Extension Amendment Proposal and the Trust Amendment Proposal.

Required Vote

        Adoption of the Adjournment Proposal requires the affirmative vote of a majority of the Ordinary Shares represented in person or by proxy and entitled to vote thereon at the extraordinary general meeting. All of the Company's directors, executive officers and their affiliates are expected to vote any Ordinary Shares owned by them in favor of the Adjournment Proposal. On the Record Date, directors and executive officers of the Company and their affiliates beneficially owned and were entitled to vote [    ·    ] founder shares representing approximately [    ·    ]% of the Company's issued and outstanding Ordinary Shares.

        In addition, the Company's directors, executive officers and their affiliates may choose to buy Ordinary Shares in the open market and/or through negotiated private purchases. In the event that purchases do occur, the purchasers may seek to purchase shares from shareholders who would otherwise have voted against the Adjournment Proposal and elected to redeem their shares into a portion of the trust account. Any Ordinary Shares purchased by affiliates prior to the Record Date will be voted in favor of the Adjournment Proposal.

Recommendation of the Board

OUR BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT OUR SHAREHOLDERS VOTE "FOR" THE APPROVAL OF THE ADJOURNMENT PROPOSAL

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THE EXTRAORDINARY GENERAL MEETING

        Date, Time and Place.    The extraordinary general meeting of the Company will be held at [    ·    ] a.m., Eastern Time on [    ·    ], 2018, at the offices of Weil, Gotshal & Manges LLP, located at 767 Fifth Avenue, New York, NY 10153.

        Voting Power; Record Date.    You will be entitled to vote or direct votes to be cast at the extraordinary general meeting, if you owned Ordinary Shares at the close of business on [    ·    ], 2018, the Record Date for the extraordinary general meeting. At the close of business on the Record Date, there were [    ·    ] issued and outstanding Ordinary Shares each of which entitles its holder to cast one vote per proposal. Company warrants do not carry voting rights.

        Proxies; Board Solicitation.    Your proxy is being solicited by the Company's board of directors on the Extension Amendment Proposal, the Trust Amendment Proposal and the Adjournment Proposal being presented to shareholders at the extraordinary general meeting. No recommendation is being made as to whether you should elect to redeem your shares. Proxies may be solicited in person or by telephone. If you grant a proxy, you may still revoke your proxy and vote your shares in person at the extraordinary general meeting.

        The Company has hired MacKenzie Partners, Inc. to assist in the proxy solicitation process for this extraordinary general meeting and for the meeting the Company will hold in connection with the Organogenesis Transaction, or any other proposed business combination. The Company will pay that firm a fee of $[    ·    ] plus disbursements for its services for these two meetings.

Interests of the Company's Directors and Officers

        When you consider the recommendation of the Company's board of directors, you should keep in mind that the Company's executive officers and members of the Company's board of directors have interests that may be different from, or in addition to, your interests as a shareholder. These interests include, among other things:

•

if the Extension Amendment Proposal and the Trust Amendment Proposal are not approved and we do not consummate a business combination by October 14, 2018 as contemplated by our IPO prospectus and in accordance with our Articles, the [    ·    ] founder shares held by the Company's officers, directors and affiliates and their permitted transferees, which were acquired prior to the IPO for an aggregate purchase price of $25,000, will be worthless (as the holders have waived liquidation rights with respect to such shares), as will the 16,400,000 private placement warrants that were acquired simultaneously with the IPO for an aggregate purchase price of $8,200,000 (as they will expire). Such founder shares and units had an aggregate market value of approximately $[    ·    ] based on the last sale price of $[    ·    ] and $[    ·    ] of the public shares and warrants, respectively, on Nasdaq on [    ·    ], 2018;



•

the fact that the initial shareholders have agreed not to redeem any of the founder shares in connection with a shareholder vote to approve a proposed initial business combination;



•

the fact that AHPAC issued to the sponsor on August 11, 2017, as amended and restated on May 3, 2018, an unsecured promissory note pursuant to which AHPAC is permitted to borrow up to $600,000 in aggregate principal amount;



•

the fact that the initial shareholders have agreed to waive their rights to liquidating distributions from the trust account with respect to their founder shares if AHPAC fails to complete an initial business combination by October 14, 2018;



•

the fact that if AHPAC consummates a business combination, any amounts outstanding under any loan made by the sponsor to AHPAC will be repayable in cash or at the option of the sponsor, an aggregate amount up to $1,500,000 may be converted into warrants with identical

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terms as the private placement warrants, at the price of $0.50 per warrant, and if AHPAC fails to complete a business combination there may be insufficient assets outside the trust account to satisfy such loans;

•

the fact that if AHPAC consummates the Organogenesis Transaction, the initial shareholders will surrender to AHPAC an aggregate 6,359,007 AHPAC Class B ordinary shares and 16,400,000 private placement warrants;



•

if the trust account is liquidated in the event AHPAC is unable to complete an initial business combination within the required time period, the sponsor has agreed to indemnify AHPAC to ensure that the proceeds in the trust account are not reduced below $10.00 per public share, or such lesser amount per public share held in the trust account as of the date of the liquidation of the trust account due to reductions in the value of the trust assets, in each case net of the interest which may be withdrawn to pay taxes, except as to any claims by a third party who executed a waiver of any and all rights to seek access to the trust account and except as to any claims under our indemnity of the underwriters of this offering against certain liabilities, including liabilities under the Securities Act;



•

the anticipated election of Mr. Joshua Tamaroff as a director of AHPAC in the Organogenesis Transaction;



•

the continued indemnification of AHPAC's existing directors and officers and the continuation of AHPAC's directors' and officers' liability insurance after the Organogenesis Transaction;



•

the fact that the sponsor, officers and directors may not participate in the formation of, or become a director or officer of, any other blank check company until AHPAC (i) has entered into a definitive agreement regarding an initial business combination or (ii) fails to complete an initial business combination by October 14, 2018; and



•

the fact that the sponsor, officers and directors will not be reimbursed for any out-of-pocket expenses if an initial business combination is not consummated by October 14, 2018.

        Additionally, if the Extension Amendment Proposal and the Trust Amendment Proposal are approved and the Company consummates an initial business combination, the officers and directors may have additional interests that would be described in the proxy statement for such transaction.

Board Recommendation

THE BOARD OF DIRECTORS UNANIMOUSLY RECOMMENDS THAT YOU VOTE "FOR" THE EXTENSION AMENDMENT PROPOSAL AND "FOR" THE TRUST AMENDMENT PROPOSAL. THE BOARD OF DIRECTORS EXPRESSES NO OPINION AS TO WHETHER YOU SHOULD REDEEM YOUR PUBLIC SHARES.

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INFORMATION ABOUT AHPAC

        AHPAC is a blank check company incorporated on December 4, 2015 as a Cayman Islands exempt company and formed for the purpose of effecting a merger, share exchange, asset acquisition, stock purchase, reorganization or similar business combination with one or more businesses, which we refer to as a "business combination." Prior to entering into the Merger Agreement, AHPAC's acquisition and value creation strategy was to identify, acquire and, after an initial business combination, build a company in the healthcare sector in public markets that complements the experience of AHPAC's management team and can benefit from AHPAC's management's operational expertise. AHPAC's acquisition selection process has leveraged its management team's network of potential transaction sources, ranging from healthcare industry executives, board members, private equity investors, wealthy families, commercial banks, investment bankers, advisors, attorneys, accountants and other transaction intermediaries. AHPAC has neither engaged in any operations nor generated any revenue to date. Based on AHPAC's business activities, we are a "shell company" as defined under the Exchange Act because AHPAC has no operations and nominal assets consisting almost entirely of cash.

        Prior to our IPO, on December 14, 2015, our sponsor purchased 8,625,000 Class B ordinary shares, for an aggregate purchase price of $25,000, or approximately $0.003 per share. In October 2016, our sponsor transferred 50,000 Class B ordinary shares to each of our independent directors at their original per share purchase price. In addition, at such time, each of our independent directors purchased an additional 421,250 Class B ordinary shares from our sponsor at their original purchase price.

        On October 14, 2016, we consummated our IPO of 30,000,000 units at a price of $10.00 per unit generating gross proceeds of $300,000,000 before underwriting discounts and expenses. Each unit ("unit") consists of one Class A Ordinary Share, par value $0.0001 per share and one warrant to purchase one-half of one Class A Ordinary Share where two warrants must be exercised for one whole Ordinary Share at an exercise price of $11.50 per whole share (each, a "public warrant"). Simultaneously with the closing of our IPO, AHPAC completed the private sale of an aggregate of 16,000,000 private placement warrants (each, a "private placement warrant"), at a purchase price of $0.50 per private placement warrant, to the initial shareholders, generating gross proceeds to AHPAC of $8,000,000.

        On November 28, 2016, we completed the sale of an additional 1,000,000 units to the underwriters of the IPO at the public offering price of $10.00 per unit pursuant to the partial exercise of the Over-allotment Option. On November 28, 2016, we sold an additional 400,000 private placement warrants for an aggregate purchase price of $200,000 in connection with the exercise of the Over-allotment Option. Following the partial exercise of the Over-allotment Option, 875,000 Class B ordinary shares were forfeited in order to maintain the ownership of the initial shareholders at 20% of the issued and outstanding ordinary shares. On November 28, 2016, our sponsor sold 161,180 Class B ordinary shares and 350,114 private placement warrants to one of our independent directors at their original purchase price. On July 5, 2017, our sponsor sold 186,320 Class B ordinary shares and 404,723 private placement warrants to one of our independent directors at their original per share purchase price.

        We received gross proceeds from the IPO, including the partial exercise of the Over-allotment Option, and the sale of the private placement warrants of $310,000,000 and $8,200,000, respectively, for an aggregate of $318,200,000. Of such amount, $310,000,000 was deposited into the trust account by trustee. The remaining $8,200,000 was held outside of the trust account, of which $6,200,000 was used to pay underwriting discounts, with the balance used to repay a note to our sponsor and to pay accrued offering and formation costs, and the remainder was reserved for business, legal and accounting due diligence on prospective acquisitions and continuing general and administrative expenses. In the future,

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a portion of interest income on the funds held in the trust account may be released to us to pay tax obligations. At June 30, 2018, funds held in the trust account consisted solely of cash.

        On November 28, 2016, we announced that, commencing November 29, 2016, holders of the 31,000,000 units sold in the IPO may elect to separately trade the public shares and public warrants included in the units. Those Units not separated will continue to trade on the NASDAQ under the symbol "AHPAU," and the public shares and warrants that are separated will trade on the NASDAQ under the symbols "AHPA" and "AHPAW," respectively.

        On August 21, 2017, the Company, Merger Sub, NewCo, Envigo, and Jermyn Street Associates, LLC, entered into the Transaction Agreement (as amended) providing for a proposed business combination. On February 14, 2018, we executed and entered into the Mutual Termination Agreement pursuant to Section 7.1(a) of the Transaction Agreement, with NewCo, Envigo, and Jermyn Street Associates, LLC, solely in its capacity as shareholder representative, for the purpose of mutually terminating the Transaction Agreement, and all proposed transactions relating to the merger. The Transaction Agreement was terminated effective as of February 14, 2018.

        On January 4, 2018, we received a letter from the staff of the Listing Qualifications Department of NASDAQ (the "Notification Letter") notifying us that we no longer comply with NASDAQ Listing Rules 5620(a) and 5810(c)(2)(G) (the "Rules") because we did not hold an annual general meeting within twelve months of the end of our fiscal year ended December 31, 2016.

        On February 21, 2018, in response to the plan we submitted to the Listing Qualifications Department of NASDAQ in response to the Notification Letter on February 20, 2018, we received a letter from the staff of the Listing Qualifications Department of NASDAQ notifying us that we have been granted an extension until June 29, 2018 to regain compliance with the Rules by holding an annual general meeting. On June 28, 2018, we held our annual general meeting.

        The mailing address of the Company's principal executive office is 65 East 55th Street, 18^th Floor, New York, New York 10022, and its telephone number is (212) 593-6900.

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BENEFICIAL OWNERSHIP OF SECURITIES

        The following table sets forth information available to us at [    ·    ], 2018 with respect to our Ordinary Shares held by:

•

each person known by us to be the beneficial owner of more than 5% of our issued and outstanding Ordinary Shares;



•

each of our officers and directors that beneficially own Ordinary Shares; and



•

all our officers and directors as a group.

        Unless otherwise indicated, we believe that all persons named in the table have sole voting and investment power with respect to all Ordinary Shares beneficially owned by them. The following table does not reflect record or beneficial ownership of the private placement warrants as they are not exercisable within 60 days of [    ·    ], 2018.

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Section 16(a) Beneficial Ownership Reporting Compliance

        Section 16(a) of the Exchange Act, as amended, requires our officers, directors and persons who beneficially own more than ten percent of our Ordinary Shares to file reports of ownership and changes in ownership with the SEC. These reporting persons are also required to furnish us with copies of all Section 16(a) forms they file. Based solely upon a review of such forms, we believe that during the year ended December 31, 2017 there were no delinquent filers.

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FUTURE SHAREHOLDER PROPOSALS

        If the Extension Amendment Proposal and the Trust Amendment Proposal are approved, the Company's 2019 annual general meeting will likely be held on or about [    ·    ], unless the date is changed by the Company's board of directors.

        Proposals that shareholders wish to include in our proxy statement and form of proxy for presentation at our 2019 Annual General Meeting must be received by us at 65 East 55th Street, 18th Floor, New York, NY 10022, Attention of Benjamin Silbert, General Counsel and Secretary no later than January 31, 2019. Any shareholder proposal must submitted be in accordance with the rules and regulations of the SEC. With respect to proposals or nominations submitted by a shareholder other than for inclusion in our 2019 proxy statement and related form of proxy, timely notice of any shareholder's intention to present such business must be received by us in accordance with our articles no later than January 31, 2019.

        If the Extension Amendment Proposal and the Trust Amendment Proposal are not approved, and we do not consummate the Organogenesis Transaction before October 14, 2018, there will be no annual general meeting in 2019.

DELIVERY OF DOCUMENTS TO SHAREHOLDERS

        Pursuant to the rules of the SEC, the Company and its agents that deliver communications to its shareholders are permitted to deliver to two or more shareholders sharing the same address a single copy of the Company's proxy statement. Upon written or oral request, the Company will deliver a separate copy of the proxy statement to any shareholder at a shared address who wishes to receive separate copies of such documents in the future. Shareholders receiving multiple copies of such documents may likewise request that the Company deliver single copies of such documents in the future. Shareholders may notify the Company of their requests by calling or writing the Company at the Company's principal executive offices at 65 East 55th Street, 18^th Floor, New York, New York 10022.

WHERE YOU CAN FIND MORE INFORMATION§

        The Company files reports, proxy statements and other information with the SEC as required by the Securities Exchange Act of 1934, as amended. You may read and copy reports, proxy statements and other information filed by the Company with the SEC at its public reference room located at 100 F Street, N.E., Washington, D.C. 20549-1004. You may obtain information on the operation of the Public Reference Room by calling the SEC at 1-800-SEC-0330. You may also obtain copies of the materials described above at prescribed rates by writing to the SEC, Public Reference Section, 100 F Street, N.E., Washington, D.C. 20549-1004. The Company files its reports, proxy statements and other information electronically with the SEC. You may access information on the Company at the SEC website containing reports, proxy statements and other information at http://www.sec.gov. This proxy statement describes the material elements of relevant contracts, exhibits and other information attached as annexes to this proxy statement. Information and statements contained in this proxy statement are qualified in all respects by reference to the copy of the relevant contract or other document included as an annex to this document.

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        This proxy statement contains important business and financial information about us that is not included in or delivered with this document. You may obtain this additional information, or additional copies of this proxy statement, at no cost, and you may ask any questions you may have about the Extension Amendment Proposal by contacting us at the following address, telephone number or facsimile number:

Avista Healthcare Public Acquisition Corp.
65 East 55th, 18^th Floor
New York, New York 10022
Attn: Benjamin Silbert
Telephone: (212) 591-6900

        In order to receive timely delivery of the documents in advance of the extraordinary general meeting, you must make your request for information no later than [    ·    ], 2018.

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ANNEX A

        AVISTA HEALTHCARE PUBLIC ACQUISITIONS CORP.
(the "Company")
SPECIAL RESOLUTION OF THE SHAREHOLDERS OF THE COMPANY

Extension Amendment Proposal

        It was resolved as a special resolution THAT, effective immediately, the Amended and Restated Memorandum and Articles of Association of the Company be amended by:

(a)

amending Article 49.4(a) by deleting the following introduction of such article:

"the Company does not consummate a Business Combination by twenty-four months after the closing of the IPO the Company shall:"

and replacing it with the following:

"the Company does not consummate a Business Combination by 15 February 2019, the Company shall"; and

(b)

amending Article 49.4(b) by deleting the words:

"within 24 months from the date of
the closing of the IPO" and

        replacing them with the words:

"by 15 February, 2019".

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ANNEX B

AMENDMENT NO. 1 TO THE INVESTMENT MANAGEMENT TRUST AGREEMENT

        This Amendment No. 1 (this "Amendment") to the Investment Management Trust Agreement (as defined below) is made by and between Avista Healthcare Public Acquisition Corp., a Cayman Islands exempted company (the "Company") and Continental Stock Transfer & Trust Company (the "Trustee"). Capitalized terms used herein but not specifically defined shall have the meanings ascribed to such terms in the Investment Management Trust Agreement.

        WHEREAS, the Company and the Trustee are parties to the Investment Management Trust Agreement, dated as of October 10, 2016 (the "Investment Management Trust Agreement");

        WHEREAS, Section 1(i) of the Investment Management Trust Agreement sets forth the terms that govern the liquidation of the Trust Account under circumstances described therein;

        WHEREAS, at an extraordinary general meeting of shareholders of the Company held on [    ·    ], 2018, the Company's shareholders approved (i) a proposal (the "Extension Amendment Proposal") to amend the Company's amended and restated memorandum and articles of association (the "Articles") to extend the date by which the Company has to consummate a business combination (the "Extension") from October 14, 2018 to February 15, 2019 (the "Extended Date") and (ii) a proposal to extend the date on which to commence liquidating the Trust Account established in connection with the Company's initial public offering in the event the Company has not consummated a business combination to the Extended Date; and

        WHEREAS, on the date hereof, the Company is filing the amendment to the Company's Articles with the Cayman Islands.

        NOW, THEREFORE, IT IS AGREED:

        1.     Section 1(i) of the Investment Management Trust Agreement is hereby amended and restated in its entirety to read as follows:

"(i) Commence liquidation of the Trust Account only after and promptly after (x) receipt of, and only in accordance with, the terms of a letter from the Company ("Termination Letter") in a form substantially similar to that attached hereto as either Exhibit A or Exhibit B signed on behalf of the Company by its Chief Executive Officer, President, Chief Financial Officer, Secretary or Chairman of the board of directors (the "Board") of the Company or other authorized officer of the Company, and complete the liquidation of the Trust Account and distribute the Property in the Trust Account, including interest (which interest shall be net of any taxes payable and less up to $50,000 of interest that may be released to the Company to pay dissolution expenses, it being understood that the Trustee has no obligation to monitor or question the Company's position that an allocation has been made for taxes payable), only as directed in the Termination Letter and the other documents referred to therein; provided, that, in the case a Termination Letter in the form of Exhibit A is received, or (y) on February 15, 2019, if a Termination Letter has not been received by the Trustee prior to such date, in which case the Trust Account shall be liquidated in accordance with the procedures set forth in the Termination Letter attached as Exhibit B and the Property in the Trust Account, including interest (which interest shall be net of any taxes payable and less up to $50,000 of interest that may be released to the Company to pay dissolution expenses), shall be distributed to the Public Shareholders of record as of such date; provided, however, that in the event the Trustee receives a Termination Letter in a form substantially similar to Exhibit B hereto, or if the Trustee begins to liquidate the Property because it has received no such Termination Letter by February 15, 2019, the Trustee shall keep the Trust Account open until

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twelve (12) months following the date the Property has been distributed to the Public Shareholders;"

        2.     All other provisions of the Investment Management Trust Agreement shall remain unaffected by the terms hereof.

        3.     This Amendment may be signed in any number of counterparts, each of which shall be an original and all of which shall be deemed to be one and the same instrument, with the same effect as if the signatures thereto and hereto were upon the same instrument. A facsimile signature shall be deemed to be an original signature for purposes of the Amendment.

        4.     This Amendment is intended to be in full compliance with the requirements for an Amendment to the Investment Management Trust Agreement as required by Section 6(c) of the Investment Management Trust Agreement, and every defect in fulfilling such requirements for an effective amendment to the Investment Management Trust Agreement is hereby ratified, intentionally waived and relinquished by all parties hereto.

        5.     This Amendment shall be governed by and construed and enforced in accordance with the laws of the State of New York, without giving effect to conflicts of law principles that would result in the application of the substantive laws of another jurisdiction.

[The remainder of this page is intentionally left blank.]

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        IN WITNESS WHEREOF, each party has caused this Amendment to be signed by its respective officer thereunto duly authorized, all as of the date first written above.

   

[Signature Page to Amendment to Investment Management Trust Agreement]

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QuickLinks

QUESTIONS AND ANSWERS ABOUT THE EXTRAORDINARY GENERAL MEETING
THE EXTENSION AMENDMENT PROPOSAL
THE TRUST AMENDMENT PROPOSAL
THE ADJOURNMENT PROPOSAL
THE EXTRAORDINARY GENERAL MEETING
INFORMATION ABOUT AHPAC
BENEFICIAL OWNERSHIP OF SECURITIES
FUTURE SHAREHOLDER PROPOSALS
DELIVERY OF DOCUMENTS TO SHAREHOLDERS
WHERE YOU CAN FIND MORE INFORMATION§
ANNEX A
ANNEX B AMENDMENT NO. 1 TO THE INVESTMENT MANAGEMENT TRUST AGREEMENT