RA Capital, affiliates report 13M shares in Altimmune (ALT) — 6.5% stake

Rhea-AI Filing Summary

Altimmune, Inc. reporting persons RA Capital Management, L.P., RA Capital Healthcare Fund, L.P., Peter Kolchinsky and Rajeev Shah disclose beneficial ownership of 13,000,000 shares of common stock (shared voting and dispositive power). The filing states this equals 6.5% of the class, calculated using 130,105,177 shares outstanding as of March 13, 2026 and 64,250,000 shares issued in the public offering that closed on April 24, 2026. The Fund directly holds 6,500,000 shares and Common Warrants exercisable for up to 6,500,000 shares; RA Capital and the named individuals describe delegated voting/dispositive arrangements and disclaim certain beneficial‑ownership statuses for specific regulatory purposes.

Key Figures

Reported shares beneficially owned: 13,000,000 shares Percent of class: 6.5% Shares directly held by the Fund: 6,500,000 shares +3 more

6 metrics

Reported shares beneficially owned 13,000,000 shares aggregate reported on cover pages

Percent of class 6.5% calculated using outstanding and offering figures noted in filing

Shares directly held by the Fund 6,500,000 shares Fund directly holds 6,500,000 common shares

Common Warrants exercisable 6,500,000 warrants Common Warrants immediately exercisable for up to 6,500,000 shares

Shares outstanding used in calc 130,105,177 shares outstanding as of <date>March 13, 2026</date>

Shares issued in public offering 64,250,000 shares issued in offering that closed on <date>April 24, 2026</date>

Key Terms

Common Warrants, beneficially owned, shared dispositive power, Schedule 13G

4 terms

Common Warrants financial

"Common Warrants immediately exercisable for up to 6,500,000 shares"

A common warrant is a tradable instrument that gives its holder the right to buy a company’s common shares at a fixed price within a set time period, similar to a coupon that can be redeemed later to purchase stock. Investors care because exercising warrants can boost potential gains if the stock rises, but it can also dilute existing shareholders by increasing the number of shares outstanding, which can lower per-share value.

beneficially owned regulatory

"Amount beneficially owned: Row 9 of each Reporting Person's cover page"

Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.

shared dispositive power regulatory

"Shared Dispositive Power 13,000,000.00"

Schedule 13G regulatory

"Item 1. Name of issuer: Altimmune, Inc."

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Altimmune, Inc.

(Name of Issuer)

Common Stock, par value $0.0001 per share

(Title of Class of Securities)

02155H200

(CUSIP Number)

04/24/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

RA Capital Management, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 13,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,000,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

6.5 %

12

Type of Reporting Person (See Instructions)

IA, PN

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Peter Kolchinsky

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 13,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,000,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

6.5 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Rajeev Shah

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 13,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,000,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

6.5 %

12

Type of Reporting Person (See Instructions)

HC, IN

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

RA Capital Healthcare Fund, L.P.

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 13,000,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,000,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,000,000.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

6.5 %

12

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Altimmune, Inc.
(b)	Address of issuer's principal executive offices: 910 CLOPPER ROAD, SUITE 201S, GAITHERSBURG, MD, 20878.
Item 2.
(a)	Name of person filing: The names of the persons filing this report (collectively, the "Reporting Persons") are: RA Capital Management, L.P. ("RA Capital") Peter Kolchinsky ("Dr. Kolchinsky") Rajeev Shah ("Mr. Shah") RA Capital Healthcare Fund, L.P. (the "Fund") The Reporting Persons expressly disclaim status as a "group" for purposes of this Schedule 13G.
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is: c/o RA Capital Management, L.P., 200 Berkeley Street, 18th Floor, Boston MA 02116
(c)	Citizenship: RA Capital and the Fund are Delaware limited partnerships. Dr. Kolchinsky and Mr. Shah are United States citizens.
(d)	Title of class of securities: Common Stock, par value $0.0001 per share
(e)	CUSIP Number(s): 02155H200
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: Row 9 of each Reporting Person's cover page to this Schedule 13G sets forth the aggregate number of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The Fund directly holds (i) 6,500,000 shares of common stock and (ii) common stock warrants (the "Common Warrants") immediately exercisable for up to 6,500,000 shares of common stock. RA Capital Healthcare Fund GP, LLC is the general partner of the Fund. The general partner of RA Capital is RA Capital Management GP, LLC, of which Dr. Kolchinsky and Mr. Shah are the controlling persons. RA Capital serves as investment adviser for the Fund and may be deemed a beneficial owner, for purposes of Section 13(d) of the Act, of any securities of the Issuer held by the Fund. The Fund has delegated to RA Capital the sole power to vote and the sole power to dispose of all securities held in the Fund's portfolio, including the shares of the Issuer's common stock reported herein. Because the Fund has divested voting and investment power over the reported securities it holds and may not revoke that delegation on less than 61 days' notice, the Fund disclaims beneficial ownership of the securities it holds for purposes of Section 13(d) of the Act. As managers of RA Capital, Dr. Kolchinsky and Mr. Shah may be deemed beneficial owners, for purposes of Section 13(d) of the Act, of any securities of the Issuer beneficially owned by RA Capital. RA Capital, Dr. Kolchinsky, and Mr. Shah disclaim beneficial ownership of the securities reported in this Schedule 13G other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13G shall not be deemed an admission that either RA Capital, Dr. Kolchinsky, or Mr. Shah is the beneficial owner of such securities for any other purpose.
(b)	Percent of class: Row 11 of each Reporting Person's cover page to this Schedule 13G sets forth the percentages of shares of common stock of the Issuer beneficially owned by such Reporting Person and is incorporated by reference. The percentage set forth in each row 11 is based upon the sum of (i) 130,105,177 shares of common stock outstanding as of March 13, 2026, as reported in the Issuer's definitive proxy statement, filed with the Securities and Exchange Commission (the "SEC") on March 17, 2026 and (ii) 64,250,000 shares of common stock issued in the Issuer's public offering of equity securities that closed on April 24, 2026, as reported in the Issuer's Current Report on Form 8-K filed with the SEC on April 24, 2026, and giving effect to Common Warrants, to the extent exercisable within 60 days hereof, as referenced herein.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: Row 5 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(ii) Shared power to vote or to direct the vote: Row 6 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to vote or to direct the vote of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(iii) Sole power to dispose or to direct the disposition of: Row 7 of each Reporting Person's cover page to this Schedule 13G sets forth the sole power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
	(iv) Shared power to dispose or to direct the disposition of: Row 8 of each Reporting Person's cover page to this Schedule 13G sets forth the shared power to dispose or to direct the disposition of securities of the Issuer beneficially owned by such Reporting Person and is incorporated by reference.
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	Not Applicable
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under ?? 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

RA Capital Management, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By Peter Kolchinsky, Authorized Signatory
Date:	05/01/2026

Peter Kolchinsky

Signature:	/s/ Peter Kolchinsky
Name/Title:	Peter Kolchinsky
Date:	05/01/2026

Rajeev Shah

Signature:	/s/ Rajeev Shah
Name/Title:	Rajeev Shah
Date:	05/01/2026

RA Capital Healthcare Fund, L.P.

Signature:	/s/ Peter Kolchinsky
Name/Title:	By RA Capital Healthcare Fund GP, LLC, its General Partner, By Peter Kolchinsky, Manager
Date:	05/01/2026

Exhibit Information

Exhibit 99.1 Joint Filing Agreement