ALT · Altimmune, Inc.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The options were granted pursuant to the Company's non-employee director compensation policy.

The shares underlying the option become vested and exercisable in substantially equal monthly installments over the 12 months following May 1, 2026, subject to the reporting person's continued service through the applicable vesting date.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $3.4050 to $3.4080, inclusive. The reporting person undertakes to provide to Altimmune, Inc., any security holder of Altimmune, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in this footnote.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $3.1450 to $3.1499, inclusive. The reporting person undertakes to provide to Altimmune, Inc., any security holder of Altimmune, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in this footnote.

The price reported in Column 4 is a weighted average price. These shares were purchased in multiple transactions at prices ranging from $3.5300 to $3.5500, inclusive. The reporting person undertakes to provide to Altimmune, Inc., any security holder of Altimmune, Inc., or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares purchased at each separate price within the ranges set forth in this footnote.

The shares underlying the option become vested and exercisable over four (4) years with 25% of the shares vesting on February 26, 2027, 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.

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

The RSUs become vested over four (4) years with 25% of the shares vesting February 26, 2027, 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.

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

The RSUs become vested over four (4) years with 25% of the shares vesting February 26, 2027, 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.

The shares underlying the option become vested and exercisable over four (4) years with 25% of the shares vesting on February 26, 2027, 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.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs become vested in substantially equal annual installments over the 4 years following February 2, 2022, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

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

These shares were purchased due to participation by the reporting individual in the Issuer's 2019 Employee Stock Purchase Plan ("ESPP"). It pertains to the ESPP purchase period from August 1, 2025 through January 31, 2026.

In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the Issuer's common stock on August 1, 2025.

These shares were purchased due to participation by the reporting individual in the Issuer's 2019 Employee Stock Purchase Plan ("ESPP"). It pertains to the ESPP purchase period from August 1, 2025 through January 31, 2026

In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the Issuer's common stock on August 1, 2025

These shares were purchased due to participation by the reporting individual in the Issuer's 2019 Employee Stock Purchase Plan ("ESPP"). It pertains to the ESPP purchase period from August 1, 2025 through January 31, 2026.

In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the Issuer's common stock on August 1, 2025.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs become vested in substantially equal annual installments over the 4 years following January 30, 2023, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

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

The RSUs become vested in substantially equal annual installments over the 4 years following January 30, 2023, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

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

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

The RSUs vest in substantially equal annual installments over the 4 years following January 27, 2025, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

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

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

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs vest in substantially equal annual installments over the 4 years following January 27, 2025, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

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

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs vest in substantially equal annual installments over the 4 years following January 27, 2025, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs vest in substantially equal annual installments over the 4 years following January 25, 2024, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

The RSUs vest in substantially equal annual installments over the 4 years following January 25, 2024, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

Vesting transaction: Shares surrendered to the Issuer solely to cover taxes associated with vesting of RSUs.

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

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

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

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

The RSUs vest in substantially equal annual installments over the 4 years following January 25, 2024, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date.

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