[Form 4] Altimmune, Inc. Insider Trading Activity

Rhea-AI Filing Summary

Altimmune, Inc. insider Christophe Arbet-Engels, the company's Chief Medical Officer, reported awards on 10/01/2025 consisting of 450,000 stock options with a $3.87 exercise price and 150,000 restricted stock units (RSUs). The options vest over four years with 25% vesting on 10/01/2026 and the remainder monthly over the next 36 months, subject to continued service. The RSUs vest over four years with 25% on 10/01/2026 and the remainder in annual installments over three years and have no expiration date. The Form 4 was signed by an attorney-in-fact on 10/03/2025.

Positive

• 450,000 stock options awarded with a defined $3.87 exercise price
• 150,000 RSUs awarded that have no expiration date
• Vesting aligns with service: 25% vests on 10/01/2026 for both options and RSUs

Negative

• None.

Insights

Compensation Governance Analyst

Grant of long-term equity tied to service over four years.

The Form 4 discloses a standard executive equity package: 450,000 options at a $3.87 exercise price and 150,000 RSUs, both awarded on 10/01/2025. Vesting schedules align incentives with continued employment, with 25% vesting on 10/01/2026.

This matters for governance because the awards increase the reporting person’s potential future equity stake and align compensation with multi-year performance without providing immediate liquidity.

Equity Dilution Specialist

Potential share count increase of 600,000 underlying shares if fully vested and exercised.

The Form 4 shows 450,000 options and 150,000 RSUs, which together represent 600,000 shares underlying these instruments. Options have a defined exercise price ($3.87); RSUs convert to shares when vested and have no expiration.

For investors, the key disclosed metric is the exact number of shares that could be issued over time; the filing does not disclose current total outstanding shares, so the percentage dilution cannot be computed from this form alone.

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

OMB Number:			3235-0287
Estimated average burden
hours per response:			0.5

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

1. Name and Address of Reporting Person^*

Arbet-Engels Christophe

(Last) (First) (Middle)

C/O ALTIMMUNE, INC.

910 CLOPPER ROAD, SUITE 201S

(Street)

GAITHERSBURG MD 20878

(City) (State) (Zip)

2. Issuer Name and Ticker or Trading Symbol
Altimmune, Inc. [ ALT ]

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

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

3. Date of Earliest Transaction (Month/Day/Year)
10/01/2025

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

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
Stock Options (option to buy)	$3.87	10/01/2025		A		450,000		(1)	10/01/2035	Common Stock, par value $0.0001	450,000	$0.00	450,000	D
Restricted Stock Units	(2)	10/01/2025		A		150,000		(3)	(3)	Common Stock, par value $0.0001	150,000	$0.00	150,000	D

Explanation of Responses:

1. The shares underlying the option become vested and exercisable over four (4) years with 25% of the shares vesting on October 1, 2026, with the remainder vesting in equal monthly installments for the following thirty-six (36) months, subject to the reporting person's continued service on each applicable vesting date.

2. Each Restricted Stock Unit ("RSU") represents a contingent right to receive one share of Common Stock, par value $0.0001, when vested

3. The RSUs become vested over four (4) years with 25% of the shares vesting October 1, 2026, with the remainder vesting in equal annual installments for the following three (3) years, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

	/s/ Gregory Weaver, as Attorney-in-Fact	10/03/2025
	** 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 Altimmune insider Christophe Arbet-Engels report on Form 4 (ALT)?

He reported awards on 10/01/2025 of 450,000 stock options (exercise price $3.87) and 150,000 RSUs.

When do the newly reported options and RSUs begin to vest?

Both awards have an initial vesting of 25% on 10/01/2026; options then vest monthly over 36 months, RSUs vest in annual installments over three years.

What is the exercise price of the options reported for ALT?

The reported stock options have an exercise price of $3.87 per share.

How many total shares are underlying the awards reported on the Form 4?

The awards cover a total of 600,000 underlying shares: 450,000 from options and 150,000 from RSUs.

Does the Form 4 disclose when it was filed or signed?

The Form 4 shows the awards dated 10/01/2025 and a signature by attorney-in-fact on 10/03/2025.