Assembly Biosciences Highlights Presentations on Positive Phase 1b Data for ABI-5366 and ABI-1179 in Recurrent Genital Herpes at ESCMID Global 2026

– Additional Phase 1b data for ABI-5366, including results from monthly dosing cohort, selected for oral presentation –

– Phase 1b data from ABI-1179 accepted for late-breaker poster presentation –

SOUTH SAN FRANCISCO, Calif., April 09, 2026 — Assembly Biosciences, Inc. (Nasdaq: ASMB), a biotechnology company developing innovative therapeutics targeting serious viral diseases, today announced Phase 1b clinical data for ABI-5366 and ABI-1179, herpes simplex virus (HSV) helicase-primase inhibitor candidates, will be featured in multiple presentations, including one late-breaker, at the 2026 Congress of the European Society of Clinical Microbiology and Infectious Diseases (ESCMID) taking place April 17-21, 2026, in Munich, Germany.

“The selection of ABI-5366 for oral presentation at ESCMID underscores the strength and clinical relevance of the data generated to date, including additional results from the monthly dosing cohort,” said Anuj Gaggar, MD, PhD, chief medical officer of Assembly Bio. “We are also pleased to see the first scientific presentation of Phase 1b data for ABI-1179 recognized as a late-breaker presentation, which highlight its potential as a long-acting therapeutic option for patients with recurrent genital herpes.”

Details of the presentations are as follows:

ABI-5366:

• Oral Presentation: ABI-5366-101: a phase 1b study of a novel, oral, long-acting, investigational HSV helicase-primase inhibitor in recurrent genital herpes Presenter: Mark Bloch, MBBS, Momentum Clinical Research and Kirby Institute, University of New South Wales Session Date and Time: April 20, 2026, at 5:30 PM CEST
• Poster Presentation: Virologic analyses following treatment with ABI-5366, a novel, oral, long-acting HSV helicase-primase inhibitor in participants seropositive for HSV-2 with recurrent genital herpes Presenter: Kathryn Kitrinos, PhD, Assembly Bio Session Date and Time: April 18, 2026, at 12:00 PM CEST
• Poster Presentation: The safety and tolerability of ABI-5366, a novel, oral, long-acting HSV helicase-primase inhibitor in participants with recurrent genital herpes Presenter: Cory Sellwood, MBBS, New Zealand Clinical Research Session Date and Time: April 18, 2026, at 12:00 PM CEST

ABI-1179:

• Poster Presentation (Late-Breaker): The safety and efficacy of ABI-1179, a novel, oral, long-acting HSV helicase-primase inhibitor for recurrent genital herpes: interim results from a phase 1b study Presenter: Mark Bloch, MBBS, Momentum Clinical Research and Kirby Institute, University of New South Wales Session Date and Time: April 21, 2026, at 12:00 PM CEST

Assembly Bio intends to make the posters available on the “Events & Presentations” page in the “Investors” section and on the “Publications” page in the “Pipeline” section of its website at www.assemblybio.com.

ABI-5366 and ABI-1179 are investigational product candidates that have not been approved anywhere globally, and their safety and efficacy have not been established. They are exclusively licensed to Gilead Sciences, Inc. (Gilead) under the collaboration between Assembly Bio and Gilead, and Gilead has the sole right and responsibility for further clinical development and commercialization of these programs.

About Assembly Biosciences

Assembly Biosciences is a biotechnology company dedicated to the development of innovative small-molecule therapeutics designed to change the path of serious viral diseases and improve the lives of patients worldwide. Led by an accomplished team of leaders in virologic drug development, Assembly Bio is committed to improving outcomes for patients struggling with the serious, chronic impacts of herpesvirus, hepatitis B virus (HBV) and hepatitis delta virus (HDV) infections. For more information, visit assemblybio.com.

Contacts

Investors:

Patrick Till Meru Advisors (484) 788-8560 [email protected]

Media:

Sam Brown LLC Alyssa Kuciunas (331) 481-3751 [email protected]