– Event to highlight recurrent CDI market opportunity and SER-109 launch preparations –

Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading microbiome therapeutics company, today announced that it will host an investor webcast to discuss the planned commercialization approach and market opportunity for therapeutic candidate SER-109 in recurrent C. difficile infection (rCDI) on Thursday, December 8, 2022, at 8:30 a.m. ET and is expected to be approximately one hour in duration.

In October 2022, Seres announced its Biologics License Application for SER-109 was accepted for Priority Review by the FDA and that a Prescription Drug User Fee Act (PDUFA) action date has been set for April 26, 2023. SER-109 is an investigational microbiome therapeutic composed of purified Firmicutes spores to prevent recurrence of rCDI. The SER-109 Phase 3 ECOSPOR III study results, initially published in the New England Journal of Medicine (NEJM), showed that 88% of SER-109 patients achieved a sustained clinical response compared to 60% on placebo at eight weeks. SER-109 was observed to be well tolerated with no drug-related serious adverse events.

The SER-109 investor webcast will include members of management from Seres Therapeutics, Aimmune Therapeutics, Inc., a Nestlé Health Science Company, as well as Carl Crawford M.D. Assistant Professor of Clinical Medicine at Weill Cornell Medical College. The event will review unmet needs in rCDI, SER-109 clinical data, and potential commercialization plans for SER-109, if approved.

Webcast Information

To join the live webcast, please visit the “Investors and News” section of the Seres website at www.serestherapeutics.com. To access the event via conference call, please dial 800-715-9871 (domestic) or 646 307-1963 (international) and reference the conference ID number 3567655.

A webcast replay will be available on the Seres website beginning approximately two hours after the event and will be archived for approximately 21 days.

About Seres Therapeutics

Seres Therapeutics, Inc. (Nasdaq: MCRB) is a leading microbiome therapeutics company developing a novel class of multifunctional bacterial consortia that are designed to functionally interact with host cells and tissues to treat disease. Seres’ SER-109 program achieved the first-ever positive pivotal clinical results for a targeted microbiome drug candidate and has obtained Breakthrough Therapy and Orphan Drug designations from the FDA. The SER-109 program is being advanced to prevent further recurrences of C. difficile infection and has potential to become a first-in-class FDA-approved oral microbiome therapeutic. Seres is evaluating SER-155 in a Phase 1b study in patients receiving allogeneic hematopoietic stem cell transplantation to reduce incidences of gastrointestinal infections, bloodstream infections and graft-versus-host disease as well as additional preclinical stage programs targeting Infection Protection in medically compromised patients. The Company is also conducting research to inform further development of microbiome therapeutics for ulcerative colitis.

For more information, please visit www.serestherapeutics.com.

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