[Form 4] Metsera, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Metsera, Inc. (MTSR) reported insider transactions on Form 4 tied to its merger closing with Pfizer on 11/13/2025. At the effective time, each issued and outstanding Metsera common share was converted into the right to receive $65.60 in cash per share, plus one contingent value right (CVR) payable upon specified milestones.

The filing lists holdings associated with Population Health Partners: 12,639,787 shares recorded by Population Health Partners, L.P. and 127,675 shares recorded by Population Health Partners GP, LLC. Following the reported transaction, the filing shows 0 shares beneficially owned by the reporting person.

SEC Form 4

FORM 4

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

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934
or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL

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X

Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).

Check this box to indicate that a transaction was made pursuant to a contract, instruction or written plan for the purchase or sale of equity securities of the issuer that is intended to satisfy the affirmative defense conditions of Rule 10b5-1(c). See Instruction 10.

1. Name and Address of Reporting Person^*

Population Health Partners GP, LLC

(Last) (First) (Middle)

1200 MORRIS TURNPIKE, SUITE 300

(Street)

SHORT HILLS NJ 07078

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Metsera, Inc. [ MTSR ]

5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)

	Director	X	10% Owner
	Officer (give title below)		Other (specify below)

3. Date of Earliest Transaction (Month/Day/Year)
11/13/2025

4. If Amendment, Date of Original Filed (Month/Day/Year)

6. Individual or Joint/Group Filing (Check Applicable Line)

X	Form filed by One Reporting Person
	Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1. Title of Security (Instr. 3)	2. Transaction Date (Month/Day/Year)	2A. Deemed Execution Date, if any (Month/Day/Year)	3. Transaction Code (Instr. 8)		4. Securities Acquired (A) or Disposed Of (D) (Instr. 3, 4 and 5)			5. Amount of Securities Beneficially Owned Following Reported Transaction(s) (Instr. 3 and 4)	6. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	7. Nature of Indirect Beneficial Ownership (Instr. 4)
			Code	V	Amount	(A) or (D)	Price
Common Stock(3)	11/13/2025		D(1)(2)		127,675	D	(1)(2)	0	D
Common Stock(3)	11/13/2025		D(1)(2)		12,639,787	D	(1)(2)	0	I	By Population Health Partners, L.P.

Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 3)	2. Conversion or Exercise Price of Derivative Security	3. Transaction Date (Month/Day/Year)	3A. Deemed Execution Date, if any (Month/Day/Year)	4. Transaction Code (Instr. 8)		5. Number of Derivative Securities Acquired (A) or Disposed of (D) (Instr. 3, 4 and 5)		6. Date Exercisable and Expiration Date (Month/Day/Year)		7. Title and Amount of Securities Underlying Derivative Security (Instr. 3 and 4)		8. Price of Derivative Security (Instr. 5)	9. Number of derivative Securities Beneficially Owned Following Reported Transaction(s) (Instr. 4)	10. Ownership Form: Direct (D) or Indirect (I) (Instr. 4)	11. Nature of Indirect Beneficial Ownership (Instr. 4)
				Code	V	(A)	(D)	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

Explanation of Responses:

1. Pursuant to the Agreement and Plan of Merger dated September 21, 2025, as amended on November 7, 2025 (the "Merger Agreement"), by and among Metsera, Inc. (the "Company"), Pfizer Inc., a Delaware corporation ("Parent"), and Mayfair Merger Sub, Inc., a Delaware corporation and a wholly owned subsidiary of the Parent (the "Merger Sub"), the Merger Sub merged with and into the Company, with the Company continuing as the surviving corporation and a wholly owned subsidiary of the Parent (the "Merger"). At the Effective Time of the Merger (as defined in the Merger Agreement), each issued and outstanding share of common stock, par value $0.00001 per share of the Company (the "Common Stock") was converted automatically into the right to receive (i) cash in an amount equal to $65.60 per share without interest (the "Closing Amount"),

2. (Continued from footnote 1) net of all applicable withholding taxes, plus (ii) one contractual contingent value right representing the right to receive contingent payments (a "CVR") in cash, without interest, upon the achievement of certain specified milestones, in accordance with the terms and conditions of the contingent value rights agreement entered into by the Parent and Equiniti Trust Company, LLC, dated November 13, 2025 (collectively, the "Merger Consideration").

3. Population Health Partners, L.P. ("PHP LP") is the record owner of 12,639,787 shares of the Common Stock and Population Health Partners GP, LLC ("PHP GP LLC") is the record owner of 127,675 shares of the Common Stock. PHP GP LLC is the sole general partner of PHP LP and may be deemed to beneficially own the shares of the Common Stock held by PHP LP. Christopher Whitten Bernard, Christopher T. Cox and Clive A. Meanwell are members of PHP GP LLC and may be deemed to share the power to direct the disposition and vote of the shares of Common Stock held by PHP LP and PHP GP LLC. Each of PHP GP LLC, Christopher Whitten Bernard, Christopher T. Cox and Clive A. Meanwell disclaims beneficial ownership of the reported securities except to the extent of its pecuniary interest therein, and this report shall not be deemed an admission that it is the beneficial owner of the securities for purposes of Section 16 of the Securities Exchange Act of 1934, as amended, or for any other purpose.

	/s/ Christopher Cox, Member of Population Health Partners GP, LLC	11/13/2025
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 4 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.

FAQ

What did Metsera (MTSR) disclose in this Form 4?

It reported dispositions of common stock at the merger closing, where each share converted to $65.60 cash plus one CVR.

What consideration did Metsera shareholders receive in the Pfizer merger?

Each share converted into the right to receive $65.60 in cash without interest, plus one CVR tied to milestones.

When did the Metsera merger close?

The effective time referenced in the filing is 11/13/2025.

How many shares were recorded by Population Health Partners entities?

Population Health Partners, L.P. held 12,639,787 shares and Population Health Partners GP, LLC held 127,675 shares.

How many shares did the reporting person hold after the transaction?

The filing shows 0 shares beneficially owned following the reported transaction(s).

Who were the merger parties named?

Metsera, Inc., Pfizer Inc. (Parent), and Mayfair Merger Sub, Inc., a wholly owned subsidiary of Pfizer.