Viking Global (NASDAQ: ALT) reports 6.7% Altimmune stake, 6.7M warrants

Rhea-AI Filing Summary

Altimmune, Inc. ownership filing: an investment group led by Viking Global reports beneficial ownership of 13,400,000 shares of Altimmune common stock, representing 6.7% of the class based on 194,199,358 shares outstanding as of April 24, 2026. The holdings reflect 4,690,000 shares owned by Viking Global Opportunities (VGOP) and 2,010,000 shares owned by Viking Global Opportunities Vintage IV (VGOVIV), plus corresponding 6,700,000 warrants exercisable at $3.00 per share that give the reporting group the right to purchase additional shares. Ownership is reported across multiple related entities and two named individuals as shared voting and dispositive power.

Insights

Institutional Ownership Analyst

Viking Global reports a 6.7% beneficial position in Altimmune across related entities.

The filing shows a consolidated beneficial interest of 13,400,000 shares and rights to purchase 6,700,000 warrants at $3.00, with shared voting and dispositive power across several Viking-controlled entities. Percentages use the issuer's reported post-offering outstanding share count.

Implications are procedural: this is a disclosure of a substantial holder under Section 13 rules. Subsequent filings would show any changes in voting or disposition; timing and cash‑flow treatment are not stated in the excerpt.

Key Figures

Shares beneficially owned: 13,400,000 shares Percent of class: 6.7% Shares outstanding: 194,199,358 shares +3 more

6 metrics

Shares beneficially owned 13,400,000 shares consolidated holdings reported by Viking Global entities

Percent of class 6.7% based on 194,199,358 shares outstanding as of April 24, 2026

Shares outstanding 194,199,358 shares post-underwritten offering outstanding reported April 24, 2026

Warrants exercisable 6,700,000 shares rights to purchase upon exercise of warrants at $3.00 per share

VGOP direct holdings 4,690,000 shares directly owned by VGOP per filing

VGOVIV direct holdings 2,010,000 shares directly owned by VGOVIV per filing

Key Terms

beneficially owned, shared dispositive power, warrants, Rule 13d-3

4 terms

beneficially owned regulatory

"VGI beneficially owns 13,400,000 shares of Common Stock"

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 13,400,000.00"

warrants financial

"warrants to purchase shares of Common Stock at an exercise price of $3.00 per share"

Warrants are special documents that give you the right to buy a company's stock at a set price before a certain date. They are often used as a way for companies to attract investors or raise money, and their value can increase if the company's stock price goes up.

Rule 13d-3 regulatory

"Based on Rule 13d-3 under the Act, VGI may be deemed to beneficially own"

Rule 13d-3 defines who is treated as the beneficial owner of a company’s shares for U.S. securities disclosure rules — essentially anyone who has the power to vote or direct how shares are voted, or the power to buy or sell them, even if they don’t hold the certificates. For investors this matters because crossing certain ownership thresholds triggers public filing and disclosure obligations and signals potential control or influence, much like having the keys to a car implies you can drive it even if it’s registered to someone else.

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

VIKING GLOBAL INVESTORS LP

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 13,400,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,400,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,400,000.00

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)

6.7 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Parent GP LLC

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 13,400,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,400,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,400,000.00

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)

6.7 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities GP LLC

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 9,380,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 9,380,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

9,380,000.00

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)

4.7 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Portfolio GP LLC

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 9,380,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 9,380,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

9,380,000.00

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)

4.7 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Illiquid Investments Sub-Master LP

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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 9,380,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 9,380,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

9,380,000.00

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)

4.7 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Vintage IV GP LLC

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 4,020,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,020,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,020,000.00

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)

2 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Vintage IV Portfolio GP LLC

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 4,020,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,020,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,020,000.00

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)

2 %

12

Type of Reporting Person (See Instructions)

OO

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Viking Global Opportunities Vintage IV (Aggregator) LP

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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 4,020,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 4,020,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

4,020,000.00

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)

2 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

HALVORSEN OLE ANDREAS

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

NORWAY

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 0.00
6	Shared Voting Power 13,400,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,400,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,400,000.00

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)

6.7 %

12

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

CUSIP Number(s): 02155H200

1

Names of Reporting Persons

Shabet Rose Sharon

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 13,400,000.00
7	Sole Dispositive Power 0.00
8	Shared Dispositive Power 13,400,000.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

13,400,000.00

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)

6.7 %

12

Type of Reporting Person (See Instructions)

IN

Comment for Type of Reporting Person: See Item 4

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Altimmune, Inc.
(b)	Address of issuer's principal executive offices: 910 Clopper Road, Suite 201S, Gaithersburg, Maryland 20878
Item 2.
(a)	Name of person filing: Viking Global Investors LP ("VGI"), Viking Global Opportunities Parent GP LLC ("Opportunities Parent"), Viking Global Opportunities GP LLC ("Opportunities GP"), Viking Global Opportunities Portfolio GP LLC ("Opportunities Portfolio GP"), Viking Global Opportunities Illiquid Investments Sub-Master LP ("VGOP"), Viking Global Opportunities Vintage IV GP LLC ("VGOVIV GP"), Viking Global Opportunities Vintage IV Portfolio GP LLC ("VGOVIV Portfolio GP"), Viking Global Opportunities Vintage IV (Aggregator) LP ("VGOVIV"), O. Andreas Halvorsen and Rose S. Shabet (collectively, the "Reporting Persons")
(b)	Address or principal business office or, if none, residence: The business address of each of the Reporting Persons is: 600 Washington Boulevard, Floor 11, Stamford, Connecticut 06901.
(c)	Citizenship: VGI is a Delaware limited partnership; Opportunities Parent, Opportunities GP, Opportunities Portfolio GP, VGOVIV GP and VGOVIV Portfolio GP are Delaware limited liability companies; VGOP and VGOVIV are Cayman Islands exempted limited partnerships; O. Andreas Halvorsen is a citizen of Norway; and Rose S. Shabet is a citizen of the United States.
(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: This Statement on Schedule 13G relates to shares of Common Stock and warrants to purchase shares of Common Stock at an exercise price of $3.00 per share (the "Warrants") held directly by VGOP and VGOVIV. VGI: 13,400,000 VGI provides managerial services to VGOP and VGOVIV. VGI has the authority to dispose of and vote the shares of Common Stock that VGOP and VGOVIV directly own or have the right to purchase upon exercise of the Warrants. VGI does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Securities Exchange Act of 1934, as amended (the "Act"), VGI may be deemed to beneficially own the shares of Common Stock that VGOP and VGOVIV directly own or have the right to purchase upon exercise of the Warrants. VGI beneficially owns 13,400,000 shares of Common Stock consisting of (i) 4,690,000 and 2,010,000 shares of Common Stock directly owned by VGOP and VGOVIV, respectively, and (ii) 4,690,000 and 2,010,000 shares of Common Stock beneficially owned by VGOP and VGOVIV, respectively, which VGOP and VGOVIV have the right to purchase upon exercise of the Warrants. Opportunities Parent: 13,400,000 Opportunities Parent is the sole member of Opportunities GP, which has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP (which consists of the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants), and is the sole member of VGOVIV GP, which has the authority to dispose of and vote the shares of Common Stock controlled by VGOVIV Portfolio GP (which consists of the shares of Common Stock that VGOVIV directly owns or has the right to purchase upon exercise of the Warrants). Opportunities Parent does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities Parent may be deemed to beneficially own the shares of Common Stock that VGOP and VGOVIV directly own or have the right to purchase upon exercise of the Warrants. Opportunities Parent beneficially owns 13,400,000 shares of Common Stock consisting of (i) 4,690,000 and 2,010,000 shares of Common Stock directly owned by VGOP and VGOVIV, respectively, and (ii) 4,690,000 and 2,010,000 shares of Common Stock beneficially owned by VGOP and VGOVIV, respectively, which VGOP and VGOVIV have the right to purchase upon exercise of the Warrants. Opportunities GP: 9,380,000 Opportunities GP serves as the sole member of Opportunities Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by Opportunities Portfolio GP, which consists of the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. In addition, Opportunities GP is the general partner of each of Viking Global Opportunities Intermediate LP, Viking Global Opportunities III LP, and Viking Global Opportunities LP. Opportunities GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities GP may be deemed to beneficially own the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities GP beneficially owns 9,380,000 shares of Common Stock consisting of 4,690,000 shares of Common Stock directly owned by VGOP and 4,690,000 shares of Common Stock beneficially owned by VGOP, which VGOP has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP: 9,380,000 Opportunities Portfolio GP serves as the general partner of VGOP and has the authority to dispose of and vote the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, Opportunities Portfolio GP may be deemed to beneficially own the shares of Common Stock that VGOP directly owns or has the right to purchase upon exercise of the Warrants. Opportunities Portfolio GP beneficially owns 9,380,000 shares of Common Stock consisting of 4,690,000 shares of Common Stock directly owned by VGOP and 4,690,000 shares of Common Stock beneficially owned by VGOP, which VGOP has the right to purchase upon exercise of the Warrants. VGOP: 9,380,000 VGOP has the authority to dispose of and vote the 4,690,000 shares of Common Stock that it owns and the 4,690,000 shares of Common Stock it has the right to purchase upon exercise of the Warrants directly owned by it, which power may be exercised by its general partner, Opportunities Portfolio GP, and by VGI, an affiliate of Opportunities Portfolio GP, which provides managerial services to VGOP. Viking Global Opportunities LP (a Delaware limited partnership) and Viking Global Opportunities III LP (a Cayman Islands exempted limited partnership), through its investment in Viking Global Opportunities Intermediate LP (a Cayman Islands exempted limited partnership), invest substantially all of their assets in Viking Global Opportunities Master LP (a Cayman Islands exempted limited partnership), which in turn invests through VGOP. VGOVIV GP: 4,020,000 VGOVIV GP serves as the sole member of VGOVIV Portfolio GP and has the authority to dispose of and vote the shares of Common Stock controlled by VGOVIV Portfolio GP, which consists of the shares of Common Stock that VGOVIV directly owns or has the right to purchase upon exercise of the Warrants. In addition, VGOVIV GP is the general partner of each of Viking Global Opportunities Vintage IV (Offshore) LP and Viking Global Opportunities Vintage IV (Onshore) LP. VGOVIV GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, VGOVIV GP may be deemed to beneficially own the shares of Common Stock that VGOVIV directly owns or has the right to purchase upon exercise of the Warrants. VGOVIV GP beneficially owns 4,020,000 shares of Common Stock consisting of 2,010,000 shares of Common Stock directly owned by VGOVIV and 2,010,000 shares of Common Stock beneficially owned by VGOVIV, which VGOVIV has the right to purchase upon exercise of the Warrants. VGOVIV Portfolio GP: 4,020,000 VGOVIV Portfolio GP serves as the general partner of VGOVIV and has the authority to dispose of and vote the shares of Common Stock that VGOVIV directly owns or has the right to purchase upon exercise of the Warrants. VGOVIV Portfolio GP does not directly own any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, VGOVIV Portfolio GP may be deemed to beneficially own the shares of Common Stock that VGOVIV directly owns or has the right to purchase upon exercise of the Warrants. VGOVIV Portfolio GP beneficially owns 4,020,000 shares of Common Stock consisting of 2,010,000 shares of Common Stock directly owned by VGOVIV and 2,010,000 shares of Common Stock beneficially owned by VGOVIV, which VGOVIV has the right to purchase upon exercise of the Warrants. VGOVIV: 4,020,000 VGOVIV has the authority to dispose of and vote the 2,010,000 shares of Common Stock that it directly owns and the 2,010,000 shares of Common Stock it has the right to purchase upon exercise of the Warrants directly owned by it, which power may be exercised by VGOVIV Portfolio GP, and by VGI, an affiliate of VGOVIV Portfolio GP, which provides managerial services to VGOVIV. Viking Global Opportunities Vintage IV (Offshore) LP (a Cayman Islands exempted limited partnership) and Viking Global Opportunities Vintage IV (Onshore) LP (a Delaware limited partnership) invest substantially all of their assets in VGOVIV. O. Andreas Halvorsen and Rose S. Shabet: 13,400,000 Mr. Halvorsen and Ms. Shabet, as Executive Committee Members of Viking Global Partners LLC (general partner of VGI) and Opportunities Parent, have shared authority to dispose of and vote the shares of Common Stock beneficially owned by VGI and Opportunities Parent. Neither Mr. Halvorsen nor Ms. Shabet directly owns any shares of Common Stock or Warrants. Based on Rule 13d-3 under the Act, each may be deemed to beneficially own the shares of Common Stock that VGOP and VGOVIV directly own or have the right to purchase upon exercise of the Warrants. Each of Mr. Halvorsen and Ms. Shabet beneficially owns 13,400,000 shares of Common Stock consisting of (i) 4,690,000 and 2,010,000 shares of Common Stock directly owned by VGOP and VGOVIV, respectively, and (ii) 4,690,000 and 2,010,000 shares of Common Stock beneficially owned by VGOP and VGOVIV, respectively, which VGOP and VGOVIV have the right to purchase upon exercise of the Warrants.
(b)	Percent of class: The percentages set forth herein are based on (i) 194,199,358 shares of Common Stock outstanding following the Issuer's underwritten offering that closed on April 24, 2026, as reported in the Issuer's prospectus on Form 424B5, filed with the Securities and Exchange Commission (the "Commission") on April 24, 2026, and (ii) 6,700,000 shares of Common Stock that the Reporting Persons currently have the right to purchase upon exercise of the Warrants. VGI: 6.7% Opportunities Parent: 6.7% Opportunities GP: 4.7% Opportunities Portfolio GP: 4.7% VGOP: 4.7% VGOVIV GP: 2.0% VGOVIV Portfolio GP: 2.0% VGOVIV: 2.0% O. Andreas Halvorsen and Rose S. Shabet: 6.7%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOVIV GP: 0 VGOVIV Portfolio GP: 0 VGOVIV: 0 O. Andreas Halvorsen and Rose S. Shabet: 0
	(ii) Shared power to vote or to direct the vote: VGI: 13,400,000 Opportunities Parent: 13,400,000 Opportunities GP: 9,380,000 Opportunities Portfolio GP: 9,380,000 VGOP: 9,380,000 VGOVIV GP: 4,020,000 VGOVIV Portfolio GP: 4,020,000 VGOVIV: 4,020,000 O. Andreas Halvorsen and Rose S. Shabet: 13,400,000
	(iii) Sole power to dispose or to direct the disposition of: VGI: 0 Opportunities Parent: 0 Opportunities GP: 0 Opportunities Portfolio GP: 0 VGOP: 0 VGOVIV GP: 0 VGOVIV Portfolio GP: 0 VGOVIV: 0 O. Andreas Halvorsen and Rose S. Shabet: 0
	(iv) Shared power to dispose or to direct the disposition of: VGI: 13,400,000 Opportunities Parent: 13,400,000 Opportunities GP: 9,380,000 Opportunities Portfolio GP: 9,380,000 VGOP: 9,380,000 VGOVIV GP: 4,020,000 VGOVIV Portfolio GP: 4,020,000 VGOVIV: 4,020,000 O. Andreas Halvorsen and Rose S. Shabet: 13,400,000
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.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. The response to Item 4 is incorporated by reference herein.
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.

VIKING GLOBAL INVESTORS LP

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of VIKING GLOBAL INVESTORS LP (1)(2)
Date:	05/01/2026

Viking Global Opportunities Parent GP LLC

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Parent GP LLC (1)(2)
Date:	05/01/2026

Viking Global Opportunities GP LLC

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities GP LLC (1)(2)
Date:	05/01/2026

Viking Global Opportunities Portfolio GP LLC

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Portfolio GP LLC (1)(2)
Date:	05/01/2026

Viking Global Opportunities Illiquid Investments Sub-Master LP

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Illiquid Investments Sub-Master LP (1)(2)
Date:	05/01/2026

Viking Global Opportunities Vintage IV GP LLC

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Vintage IV GP LLC (1)(2)
Date:	05/01/2026

Viking Global Opportunities Vintage IV Portfolio GP LLC

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Vintage IV Portfolio GP LLC (1)(2)
Date:	05/01/2026

Viking Global Opportunities Vintage IV (Aggregator) LP

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Viking Global Opportunities Vintage IV (Aggregator) LP (1)(2)
Date:	05/01/2026

HALVORSEN OLE ANDREAS

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of O. Andreas Halvorsen (1)
Date:	05/01/2026

Shabet Rose Sharon

Signature:	/s/ Scott M. Hendler
Name/Title:	Scott M. Hendler on behalf of Rose S. Shabet (2)
Date:	05/01/2026

Comments accompanying signature: (1) Scott M. Hendler is signing on behalf of O. Andreas Halvorsen, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES VINTAGE IV GP LLC, VIKING GLOBAL OPPORTUNITIES VINTAGE IV PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES VINTAGE IV (AGGREGATOR) LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737). (2) Scott M. Hendler is signing on behalf of Rose S. Shabet, individually and as an Executive Committee Member of VIKING GLOBAL PARTNERS LLC, on behalf of VIKING GLOBAL INVESTORS LP, and as an Executive Committee Member of VIKING GLOBAL OPPORTUNITIES PARENT GP LLC, on behalf of itself and VIKING GLOBAL OPPORTUNITIES GP LLC, VIKING GLOBAL OPPORTUNITIES PORTFOLIO GP LLC, VIKING GLOBAL OPPORTUNITIES ILLIQUID INVESTMENTS SUB-MASTER LP, VIKING GLOBAL OPPORTUNITIES VINTAGE IV GP LLC, VIKING GLOBAL OPPORTUNITIES VINTAGE IV PORTFOLIO GP LLC and VIKING GLOBAL OPPORTUNITIES VINTAGE IV (AGGREGATOR) LP, pursuant to an authorization and designation letter dated February 9, 2021, which was previously filed with the Commission as an exhibit to a Form 13G filed by Mr. Halvorsen on February 12, 2021 (SEC File No. 005-49737).

Exhibit Information

EXHIBIT A - JOINT FILING AGREEMENT

FAQ

What stake does Viking Global report in Altimmune (ALT)?

Viking Global and related entities report beneficial ownership of 13,400,000 shares, representing 6.7% of common stock based on 194,199,358 shares outstanding as of April 24, 2026.

Does the filing include warrants or convertible rights for ALT?

Yes. The reporting persons state rights to purchase 6,700,000 shares upon exercise of warrants at an exercise price of $3.00 per share, which are included in their beneficial ownership calculation.

Which Viking entities hold Altimmune securities?

The reported holders include Viking Global Investors LP, Viking Global Opportunities Parent GP LLC, Opportunities GP/Portfolio GP, VGOP, and VGOVIV entities, along with two named individuals, O. Andreas Halvorsen and Rose S. Shabet.

How is voting and disposition power reported for the ALT holdings?

The filing reports shared voting and dispositive power over 13,400,000 shares for certain reporting persons; no sole voting or sole dispositive power is reported for any named filer.

What share count and date were used to compute the percentage ownership?

Percentages are based on 194,199,358 shares outstanding following the issuer's underwritten offering that closed on April 24, 2026, plus the 6,700,000 warrant shares referenced in the filing.