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As filed with the United States Securities and Exchange Commission on November 29, 2018

Registration No. 333-227090

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

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Amendment No. 5
to

FORM S-4
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

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Avista Healthcare Public Acquisition Corp.
(Exact Name of Registrant as Specified in its Charter)

65 East 55th Street
18th Floor
New York, New York 10022
(212) 593-6900
(Address, including zip code, and telephone number, including area code, of Registrant's principal executive offices)

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Ben Silbert
General Counsel and Secretary
Avista Healthcare Public Acquisition Corp.
65 East 55th Street
18th Floor
New York, NY 10022
Telephone: (212) 593-6900
Facsimile: (212) 593-6901
(Name, address, including zip code, and telephone number, including area code, of agent for service)

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Approximate date of commencement of proposed sale of the securities to the public:
As soon as practicable after this Registration Statement is declared effective and all other conditions to the business combination
described in the enclosed Joint Proxy Statement/Prospectus have been satisfied or waived.

          If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box:    o

          If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering:    o

          If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering:    o

          Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company or an emerging growth company. See the definitions of "large accelerated filer", "accelerated filer", "smaller reporting company" and "emerging growth company" in Rule 12b-2 of the Exchange Act.

          If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act.    o

          If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

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          The Registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933 or until the Registration Statement shall become effective on such date as the United States Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

   

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The Registrant intends, subject to shareholder approval, to effect a domestication under Section 388 of the Delaware General Corporation Law, pursuant to which the Registrant's state of incorporation shall be Delaware.

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EXPLANATORY NOTE

        Avista Healthcare Public Acquisition Corp. is filing this Amendment No. 5 (this "Amendment"), to its registration statement on Form S-4 (the "Registration Statement") as an exhibit-only filing to file Exhibit 99.1 and Exhibit 99.10 to the Registration Statement. Accordingly, this Amendment consists of only the cover page, this explanatory note, Part II of the Registration Statement, the signature page to the Registration Statement, Exhibit 99.1 and Exhibit 99.10. The joint proxy statement/prospectus contained in the Registration Statement is unchanged and has been omitted.

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PART II
INFORMATION NOT REQUIRED IN PROSPECTUS

Item 20.    Indemnification of Directors and Officers.

        The Companies Law of the Cayman Islands does not limit the extent to which a company's memorandum and articles of association may provide for indemnification of officers and directors. However, such provision may be held by the Cayman Islands courts to be unenforceable, to the extent it seeks to indemnify or exculpate a fiduciary in respect of their actual fraud or willful default, or for the consequences of committing a crime. The Registrant's amended and restated memorandum and articles of association provides for indemnification of officers and directors for losses, damages, costs and expenses incurred in their capacities as such, except through their own actual fraud or willful default.

        Such limitation of liability and indemnification does not affect the availability of equitable remedies. In addition, the Registrant has been advised that, in the opinion of the Securities and Exchange Commission, or the SEC, indemnification for liabilities arising under the Securities Act of 1933, as amended, or the Securities Act, is against public policy as expressed in the Securities Act and is therefore unenforceable.

Item 21.    Exhibits And Financial Statements Schedules.

(a)

Exhibits.

        The Exhibit Index following the signature page is incorporated herein by reference.

(b)

Financial Statements.

        The financial statements filed with this registration statement on Form S-4 are set forth on the Financial Statement Index and incorporated herein by reference.

Item 22.    Undertakings.

        1.     The undersigned Registrant hereby undertakes:

        (a)   To file, during any period in which offers or sales are being made, a post-effective amendment to this Registration Statement:

          (i)  To include any prospectus required by section 10(a)(3) of the Securities Act of 1933;

         (ii)  To reflect in the prospectus any facts or events arising after the effective date of this Registration Statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in this Registration Statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the Commission pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than 20% change in the maximum aggregate offering price set forth in the "Calculation of Registration Fee" table in the effective registration statement; and

        (iii)  To include any material information with respect to the plan of distribution not previously disclosed in this Registration Statement or any material change to such information in this Registration Statement.

        (b)   That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment that contains a form of prospectus shall be deemed to be a new

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registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

        (c)   To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

        (d)   That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser, each prospectus filed pursuant to Rule 424(b) as part of a registration statement relating to an offering, other than registration statements relying on Rule 430B or other than prospectuses filed in reliance on Rule 430A, shall be deemed to be part of and included in the registration statement as of the date it is first used after effectiveness. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such first use, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such date of first use.

        (e)   That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser:

          (i)  Any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424;

         (ii)  Any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant;

        (iii)  The portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and

        (iv)  Any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

        2.     Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the Registrant pursuant to the foregoing provisions, or otherwise, the Registrant has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the Registrant of expenses incurred or paid by a director, officer or controlling person of the Registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the Registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by them is against public policy as expressed in the Securities Act of 1933 and will be governed by the final adjudication of such issue.

        3.     The undersigned registrant hereby undertakes as follows: that prior to any public reoffering of the securities registered hereunder through use of a prospectus which is a part of this registration statement, by any person or party who is deemed to be an underwriter within the meaning of

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Rule 145(c), the issuer undertakes that such reoffering prospectus will contain the information called for by the applicable registration form with respect to reofferings by persons who may be deemed underwriters, in addition to the information called for by the other items of the applicable form.

        4.     The registrant undertakes that every prospectus: (1) that is filed pursuant to the immediately preceding paragraph, or (2) that purports to meet the requirements of Section 10(a)(3) of the Act and is used in connection with an offering of securities subject to Rule 415, will be filed as a part of an amendment to the registration statement and will not be used until such amendment is effective, and that, for purposes of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

        5.     The undersigned Registrant hereby undertakes to respond to requests for information that is incorporated by reference into the prospectus pursuant to Item 4, 10(b), 11 or 13 of this Form S-4, within one business day of receipt of such request, and to send the incorporated documents by first class mail or other equally prompt means. This includes information contained in documents filed subsequent to the effective date of this Registration Statement through the date of responding to the request.

        6.     The undersigned Registrant hereby undertakes to supply by means of a post-effective amendment all information concerning this transaction that was not the subject of and included in this Registration Statement when it became effective.

Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the undersigned pursuant to the foregoing provisions, or otherwise, the undersigned has been advised that in the opinion of the SEC such indemnification is against public policy as expressed in the Securities Act and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the undersigned of expenses incurred or paid by a director, officer or controlling person of the undersigned in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the undersigned will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Act and will be governed by the final adjudication of such issue.

        The undersigned registrant hereby undertakes to respond to requests for information that is incorporated by reference into the prospectus pursuant to Item 4, 10(b), 11, or 13 of this form, within one business day of receipt of such request, and to send the incorporated documents by first class mail or other equally prompt means. This includes information contained in documents filed subsequent to the effective date of the registration statement through the date of responding to the request.

        The undersigned registrant hereby undertakes to supply by means of a post-effective amendment all information concerning a transaction, and FSAC being acquired involved therein, that was not the subject of and included in the registration statement when it became effective.

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EXHIBIT INDEX

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SIGNATURES

        Pursuant to the requirements of the Securities Act of 1933, the Registrant has duly caused this Registration Statement to be signed on its behalf by the undersigned, thereunto duly authorized, in New York City, New York, on the 29th day of November, 2018.

POWER OF ATTORNEY

        KNOWN ALL MEN BY THESE PRESENTS, that each person whose signature appears below constitutes and appoints each of Benjamin Silbert and John Cafasso, each acting alone, as his true and lawful attorney-in-fact and agent, each with full power of substitution and resubstitution, for them and in their name, place and stead, in any and all capacities, to sign one or more Registration Statements on Form S-4, or other appropriate form, and all amendments thereto, including post-effective amendments, of Avista Healthcare Public Acquisition Corp. and to file the same, with any exhibits thereto, with the United States Securities and Exchange Commission, and/or any state securities department or any other federal or state agency or governmental authority granting unto such attorneys-in-fact and agents full power and authority to do and perform each and every act and thing requisite and necessary to be done in and about the premises, as fully to all intents and purposes as he might or could do in person, hereby ratifying and confirming all that said attorneys-in-fact and agents, or their substitutes, may lawfully do or cause to be done by virtue hereof.

        Pursuant to the requirements of the Securities Act of 1933, this Registration Statement has been signed below by the following persons in the capacities indicated:

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EXPLANATORY NOTE
PART II INFORMATION NOT REQUIRED IN PROSPECTUS

Item 20. Indemnification of Directors and Officers.
Item 21. Exhibits And Financial Statements Schedules.
Item 22. Undertakings.

EXHIBIT INDEX
SIGNATURES
POWER OF ATTORNEY