Armata Pharmaceuticals to Present Data at ISSSI 2026 Showing Defined Genetic Diversity in AP-SA02 May Enhance Killing of Certain Staphylococcus aureus Clinical Isolates

Controlled manufacturing reproducibly maintains defined genetic diversity across AP-SA02 clinical drug product lots

Oral presentation scheduled for today Monday, Sept. 21, 2026 at the 20 th International Symposium on Staphylococci and Staphylococcal Infections

LOS ANGELES, Sept. 21, 2026 /PRNewswire/ -- Armata Pharmaceuticals, Inc. (NYSE American: ARMP) ("Armata" or the "Company"), a late clinical-stage biotechnology company focused on the development of high-purity and potency, pathogen-specific bacteriophage therapeutics for the treatment of antibiotic-resistant and difficult-to-treat bacterial infections, today announced it will present data showing that defined, controlled genetic diversity within AP-SA02 may enhance the product's ability to kill certain Staphylococcus aureus (" S. aureus ") clinical isolates. Importantly, Armata deliberately maintains this defined genetic diversity as an important product attribute through controlled manufacturing across clinical drug product lots of AP-SA02. AP-SA02 is Armata's investigational bacteriophage cocktail being developed as an adjunct treatment for complicated bacteremia caused by methicillin-sensitive S. aureus ("MSSA") or methicillin-resistant S. aureus ("MRSA"). The findings will be presented today in an oral session at the 2026 International Symposium on Staphylococci and Staphylococcal Infections ("ISSSI 2026"), which is being held September 20-24, 2026 in Banff, Alberta, Canada.

Genomic analyses showed that AP-SA02 contains a defined and reproducible profile of genetic variants. Specifically, when one of its component phages was grown in vitro on S. aureus isolates collected during the Phase 1b/2a diSArm study, select variants became enriched depending on the isolate, suggesting that certain variants were better able to infect and replicate on particular clinical isolates. In a separate experiment, a phage stock lacking these variants showed reduced activity against select clinical isolates, further supporting functional relevance of the variants. Based on these findings, Armata uses controlled manufacturing conditions to reproducibly maintain the defined genetic variants across clinical drug product lots, making this genetic diversity an intentionally controlled attribute of AP-SA02 drug product.

Together, the genomic and functional data support controlled genetic diversity as an important product attribute that may improve the performance of AP-SA02 against certain isolates within its broad MRSA and MSSA activity profile. The in vitro findings complement the positive results from the Phase 2a diSArm study, in which 100% of AP-SA02-treated participants with an evaluable end-of-study assessment achieved a complete clinical response.

"These findings provide important mechanistic support for what we believe is a key attribute of AP-SA02: controlled genomic diversity that enables the individual phages in the cocktail to adapt to and kill a broad range of genetically and geographically diverse MRSA and MSSA clinical isolates," said Dr. Deborah Birx, Chief Executive Officer of Armata. "Importantly, the diversity profile is defined and reproducible across clinical drug product lots of AP-SA02. Together with the 100% clinical response observed in our Phase 2a diSArm study, these data further strengthen our confidence in the program as we advance AP-SA02 toward a Phase 3 superiority study in complicated S. aureus bacteremia."

20 th International Symposium on Staphylococci and Staphylococcal Infections (ISSSI 2026), September 20-24, 2026

Controlled genomic diversity in AP-SA02 bacteriophage cocktail enables adaptive amplification across diverse Staphylococcus aureus isolates

Renae Geier, Senior Scientist, Genomics, Armata Pharmaceuticals

Podium Session 2: Antistaphylococcals

Monday, Sept. 21, 2026, 5:25 p.m. to 5:40 p.m. MDT

Banff Centre for Arts and Creativity, Banff, Alberta, Canada

Armata is developing AP-SA02, a fixed multi-phage cocktail, for the adjunct treatment of complicated Staphylococcus aureus bacteremia caused by methicillin-sensitive S. aureus (MSSA) or methicillin-resistant S. aureus (MRSA). AP-SA02 has received Qualified Infectious Disease Product (QIDP), Fast Track, and Breakthrough Therapy designations from the FDA. The diSArm study (NCT05184764) was a Phase 1b/2a, multicenter, randomized, double-blind, placebo-controlled, multiple ascending dose escalation study of the safety, tolerability, and efficacy of intravenous AP-SA02 in addition to best available antibiotic therapy ("BAT") compared to BAT alone (placebo) for the treatment of adults with complicated S. aureus bacteremia. Positive results from the Phase 2a diSArm study were highlighted in a late-breaking oral presentation at IDWeek 2025™ in October 2025. The Company plans to advance AP-SA02 into a Phase 3 superiority study in complicated SAB, anticipated to initiate in the second half of 2026.

Armata is a late clinical-stage biotechnology company focused on the development of high-purity and potency, pathogen-specific bacteriophage therapeutics for the treatment of antibiotic-resistant and difficult-to-treat bacterial infections using its proprietary bacteriophage-based technology. Armata is developing and advancing a broad pipeline of natural and synthetic phage candidates, including clinical candidates for Pseudomonas aeruginosa, Staphylococcus aureus, and other important pathogens. Armata is committed to advancing phage therapy with drug development expertise that spans bench to clinic including in-house phage-specific current Good Manufacturing Practices ("cGMP") manufacturing to support full commercialization.

This communication contains "forward-looking" statements as defined by the Private Securities Litigation Reform Act of 1995. These statements relate to future events, results or to Armata's future financial performance and involve known and unknown risks, uncertainties and other factors which may cause Armata's actual results, performance or events to be materially different from any future results, performance or events expressed or implied by the forward-looking statements. In some cases, you can identify these statements by terms such as "anticipate," "believe," "could," "estimate," "expect," "intend," "may," "plan," "potential," "predict," "project," "should," "will," "would" or the negative of those terms, and similar expressions. These forward-looking statements reflect management's beliefs and views with respect to future events and are based on estimates and assumptions as of the date of this communication and are subject to risks and uncertainties including risks related to Armata's development of bacteriophage-based therapies; Armata's planned clinical trials; ability to staff and maintain its production facilities under fully compliant cGMP; ability to meet anticipated milestones in the development and testing of the relevant product; ability to be a leader in the development of phage-based therapeutics; ability to achieve its vision, including improvements through engineering and success of clinical trials; ability to successfully complete preclinical and clinical development of, and obtain regulatory approval of its product candidates and commercialize any approved products on its expected timeframes or at all; and Armata's estimates regarding anticipated operating losses, capital requirements and needs for additional funds. Additional risks and uncertainties relating to Armata and its business can be found under the caption "Risk Factors" and elsewhere in Armata's filings and reports with the U.S. Securities and Exchange Commission (the "SEC"), including in Armata's Annual Report on Form 10-K, filed with the SEC on March 25, 2026, and in its subsequent filings with the SEC.

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