X0306 4 2021-01-31 0 0001326190 Altimmune, Inc. ALT 0001742241 Brown William Michael C/O ALTIMMUNE, INC., 910 CLOPPER ROAD, SUITE 201S GAITHERSBURG MD 20878 0 1 0 0 Chief Financial Officer Common Stock, par value $0.0001 2021-01-31 4 A 0 937 12.14 A 16918 D Stock Options (option to buy) 16.71 2021-02-01 4 A 0 90000 0.00 A 2031-02-01 Common Stock, par value $0.0001 90000 90000 D Restricted Stock Units 2021-02-01 4 A 0 24664 0.00 A Common Stock, par value $0.0001 24664 24664 D 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, 2020 through January 31, 2021. In accordance with the ESPP, these shares were purchased based on 85% of the closing price of the issuer's common stock on January 31, 2021. Twenty-five percent of the shares underlying the option become vested and exercisable on February 1, 2022 and the remaining 75% of the shares underlying the option become vested and exercisable in substantially equal monthly installments over the 36 months following February 2, 2022, subject to the reporting person's continued service through the 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 and exercisable in substantially equal annual installments over the 4 years following February 2, 2021, subject to the reporting person's continued service through the applicable vesting date, and have no expiration date. /s/ William Brown 2021-02-03