Seres Therapeutics to Present Clinical Results at IDWeek and American College of Gastroenterology (ACG) 2022 Annual Meeting

Seres Therapeutics, Inc. (Nasdaq: MCRB), a leading microbiome therapeutics company, announced today that it will be presenting data from its ECOSPOR IV trial of SER-109, an investigational microbiome therapeutic for the prevention of recurrent C. difficile infection (rCDI), at two leading industry conferences: IDWeek 2022 (Washington, DC, Oct. 19-23) and the American College of Gastroenterology (ACG) 2022 Annual Meeting (Charlotte, NC, Oct. 21-26). SER-109 is an entirely new treatment modality that shows promise to improve the current standard of care for rCDI.

"These industry-leading conferences bring together the biggest and brightest minds in both infectious disease and gastroenterology, and we're excited to present new findings related to our investigational microbiome therapeutic, SER-109," said Lisa von Moltke, MD, Chief Medical Officer at Seres. "These data reinforce our belief in the potential of SER-109 to provide safe, effective treatment to prevent recurrent C. difficile infection ? an infection the CDC classified as a major health threat with nearly 170,000 annual cases in the U.S. alone."

Seres' upcoming data presentations include:

• IDWeek 2022: Oral Presentation: SER-109, an oral investigational microbiome therapy for the prevention of recurrent Clostridioides difficile infection (rCDI); October 20, 8:50 ? 9:00 AM EST; Lead Author: Barbara McGovern, MD
• ACG 2022 Annual Meeting: Oral Presentation: Plenary Session 4A - Colon / IBD; October 26, 9:50 AM ? 10:00 AM EST; Lead Author: Sahil Khanna, MBBS, MS, FACG

Seres recently announced the completion of the Biologics License Application (BLA) submission to the U.S. Food and Drug Administration (FDA) for SER-109.

About SER-109

SER-109 is an oral microbiome therapeutic candidate consisting of a consortium of highly purified Firmicutes spores, which normally live in a healthy microbiome. SER-109 is designed to prevent further recurrences of CDI by modulating the disrupted microbiome to a state that resists C. difficile colonization and growth. The SER-109 manufacturing purification process is designed to remove unwanted microbes, thereby reducing the risk of pathogen transmission beyond donor screening alone. The FDA has granted SER-109 Breakthrough Therapy designation and Orphan Drug designation for the prevention of rCDI.

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 oral FDA-approved 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.

Forward-Looking Statements

This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including the potential approval of SER-109; the potential market for SER-109; the ultimate safety profile of SER-109; the anticipated indication of SER-109; and other statements which are not historical fact.

These forward-looking statements are based on management's current expectations. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: we have incurred significant losses, are not currently profitable and may never become profitable; our need for additional funding; our limited operating history; the impact of the COVID-19 pandemic; our unproven approach to therapeutic intervention; the lengthy, expensive and uncertain process of clinical drug development; our reliance on third parties and collaborators to conduct our clinical trials, manufacture our product candidates and develop and commercialize our product candidates, if approved; and our ability to retain key personnel and to manage our growth. These and other important factors discussed under the caption "Risk Factors" in our Quarterly Report on Form 10-Q filed with the Securities and Exchange Commission, or SEC, on August 3, 2022, and our other reports filed with the SEC could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management's estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change. These forward-looking statements should not be relied upon as representing our views as of any date subsequent to the date of this press release.