Seres Therapeutics and Nestlé Health Science Present Results from ECOSPOR IV Phase 3 Study of VOWST™, a Microbiota-Based Oral Therapeutic for Prevention of Recurrence of C. Difficile Infection, at the Digestive Disease Week (DDW) Annual Meeting

– Data from Phase 3 open-label single-arm study of VOWST found nearly 95% of individuals with a clinical response at 8 weeks remained free of CDI through Week 24, regardless of number of prior C. difficile infections (CDI) –

– Results from ECOSPOR IV add to data from ECOSPOR III Phase 3 study and together supported the recent VOWST FDA approval –

Seres Therapeutics, Inc. (Nasdaq: MCRB), and Nestlé Health Science today announced the presentation of data from the Phase 3 open-label ECOSPOR IV study evaluating VOWST (fecal microbiota spores, live-brpk) – the first and only U.S. Food and Drug Administration (FDA)-approved orally administered microbiota-based therapeutic for the prevention of recurrence in adults with recurrent C. difficile (rCDI) following antibacterial treatment. VOWST is not indicated for the treatment of CDI. These data are shared as oral and poster presentations at the 2023 Digestive Disease Week® (DDW 2023) Annual Meeting being held in Chicago, Ill. on May 6-9.

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“In the ECOSPOR IV Phase 3 open-label single-arm study, high clinical response rates were achieved at week 8 and continued into week 24 following VOWST treatment, regardless of the number of prior CDI infections,” said Lisa von Moltke, M.D., Chief Medical Officer at Seres. “These results add to previous positive data from the randomized, placebo-controlled ECOSPOR III Phase 3 study. We are excited that VOWST is now approved by the FDA for the prevention of recurrent CDI following antibacterial treatment for rCDI, including in first recurrence patients.”

On April 26, VOWST was approved by the FDA for the prevention of recurrence of C. difficile infection in adults with rCDI following antibacterial treatment. The FDA approval of VOWST was supported by a robust Phase 3 development program that included the ECOSPOR III (NCT03183128) and ECOSPOR IV (NCT03183141) studies. VOWST was previously granted Breakthrough Therapy and Orphan Drug Designations by the FDA.

The data being presented at DDW include safety and efficacy data from the ECOSPOR IV study, an open-label extension study of ECOSPOR III and an open-label program evaluating VOWST in 263 adults with rCDI. ECOSPOR IV study enrolled participants with characteristics commonly seen in routine clinical practice. ECOSPOR IV results were published in JAMA Network Open¹ in February 2023. Results from ECOSPOR III were published in the New England Journal of Medicine² in January 2022.

Presentation Titles and Summaries:

Durability of the Clinical Response to SER-109, an Investigational Oral Microbiome Therapeutic, in a Phase 3 Open-Label Trial (ECOSPOR IV) in Patients with Recurrent Clostridioides Difficile Infection (Oral Presentation #694)

In the overall population of the ECOSPOR IV study (n=263), 91.3% of participants who received VOWST achieved clinical response at Week 8 and 94.6% of those participants maintained a response through Week 24. In participants with a first recurrence, response rates to VOWST were similar to the overall population with 93.5% of participants achieving a clinical response at Week 8 and 94.4% of those participants maintaining the response through Week 24. Further, in participants with two or more recurrences, 90.3% achieved a clinical response at Week 8 and 94.6% of those participants maintained that response through Week 24. These response rates were observed through Week 24, regardless of number of prior CDI recurrences.

Study populations included participants with multiple comorbidities. The most common adverse events were mild to moderate in severity and transient in nature.

Results from an Open-Label Study (ECOSPOR IV) to Evaluate the Safety and Efficacy of SER-109, an Investigational Oral Microbiome Therapeutic, in Adults with Recurrent Clostridioides Difficile Infection (rCDI): A Subgroup Analysis (Poster Presentation #Su1873)

In a post hoc subgroup analysis by select baseline characteristics, the following rates of rCDI were observed at Week 8 across all subgroups: all participants (8.7%), participants with first recurrence (6.5%) vs. those with 2 or more recurrences (9.7%), participants <65 years old (4%) vs. ≥65 years old (13.1%), participants who received vancomycin (8.9%) vs. those who received fidaxomicin (8.3%), males (10.8%) vs. females (7.8%), and those with a qualifying episode defined by PCR alone (4.3%) vs. those with a qualifying episode by toxin with/without PCR (10.4%).

Posters and presentations will be available to event attendees for 90 days on the DDW conference website.

INDICATION AND IMPORTANT SAFETY INFORMATION FOR VOWST

INDICATION

VOWST is indicated to prevent the recurrence of Clostridioides difficile infection (CDI) in individuals 18 years of age and older following antibacterial treatment for recurrent CDI (rCDI).

Limitation of Use: VOWST is not indicated for treatment of CDI.

IMPORTANT SAFETY INFORMATION

WARNINGS AND PRECAUTIONS

Transmissible infectious agents: Because VOWST is manufactured from human fecal matter, it may carry a risk of transmitting infectious agents. Report any infection that is suspected to have been transmitted by VOWST to Aimmune Therapeutics, Inc. at 1-833-246-2566.

Potential presence of food allergens: VOWST may contain food allergens. The potential to cause adverse reactions due to food allergens is unknown.

ADVERSE REACTIONS

The most common adverse reactions (reported in ≥5% of participants) were abdominal distension (31.1%), fatigue (22.2%), constipation (14.4%), chills (11.1%), and diarrhea (10.0%).

To report SUSPECTED ADVERSE REACTIONS, contact Aimmune Therapeutics at 1-833-AIM-2KNO (1-833-246-2566), or the FDA at 1-800-FDA-1088, or visit www.fda.gov/MedWatch.

DRUG INTERACTIONS

Do not administer antibacterials concurrently with VOWST.

Please see Full Prescribing Information and Patient Information

About Recurrent C. difficile Infection (rCDI)

Recurrent C. difficile infection is a gastrointestinal infection caused by C. difficile bacteria. rCDI is linked to dysbiosis of the gastrointestinal microbiome and is associated with increased morbidity and mortality. CDI has been characterized as an Urgent Health Threat by the Centers for Disease Control and Prevention (CDC). rCDI results in a substantial burden on the healthcare system³ with the average rCDI-related annual costs per patient at approximately $43K.⁴

About Seres Therapeutics

Seres Therapeutics, Inc. (Nasdaq: MCRB) is a commercial-stage company developing novel microbiome therapeutics for serious diseases. Seres’ lead program, VOWST,™ obtained U.S. FDA approval in April 2023 as the first orally administered microbiota-based therapeutic to prevent recurrence of C. difficile infection (CDI) in adults following antibacterial treatment for recurrent CDI and is being commercialized in collaboration with Nestlé Health Science. Seres is evaluating SER-155 in a Phase 1b study in patients receiving allogeneic hematopoietic stem cell transplantation. The Company is also conducting research to inform further development of microbiome therapeutics for ulcerative colitis. For more information, please visit www.serestherapeutics.com.

About Nestlé Health Science

Nestlé Health Science, a leader in the science of nutrition, is a globally managed business unit of Nestlé. We are committed to redefining the management of health, offering an extensive portfolio of science-based consumer health, medical nutrition, pharmaceutical therapies, and vitamin and supplement brands. Our extensive research network provides the foundation for products that empower healthier lives through nutrition. Headquartered in Switzerland, we have more than 12,000 employees around the world, with products available in more than 140 countries. For more information, please visit www.nestlehealthscience.us.

About Digestive Disease Week

Digestive Disease Week® (DDW) is the largest international gathering of physicians, researchers and academics in the fields of gastroenterology, hepatology, endoscopy and gastrointestinal surgery. Jointly sponsored by the American Association for the Study of Liver Diseases (AASLD), the American Gastroenterological Association (AGA), the American Society for Gastrointestinal Endoscopy (ASGE) and the Society for Surgery of the Alimentary Tract (SSAT), DDW is an in-person and online meeting from May 6-9, 2023. The meeting showcases more than 3,100 abstracts and hundreds of lectures on the latest advances in GI research, medicine and technology. More information can be found at www.ddw.org.

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 degree of market acceptance of VOWST; 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; 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; the unknown degree and competing factors of market acceptance for VOWST; the competition we will face; our ability to protect our intellectual property; 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 Annual Report on Form 10-K filed with the Securities and Exchange Commission (SEC), on March 7, 2023, 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.

References:

1. Sims MD, Khanna S, Feuerstadt P, et al. Safety and Tolerability of SER-109 as an Investigational Microbiome Therapeutic in Adults With Recurrent Clostridioides difficile Infection: A Phase 3, Open-Label, Single-Arm Trial. JAMA Network Open. 2023;6(2):e2255758. DOI: 10.1001/jamanetworkopen.2022.55758
2. Feuerstadt P, Louie TJ, Lashner B, et al. SER-109, an Oral Microbiome Therapy for Recurrent Clostridioides difficile Infection. N Engl J Med. 2022;386:220-9. DOI: 10.1056/nejmoa2106516
3. Rodrigues R, Barber GE, Ananthakrishnan AN. A Comprehensive Study of Costs Associated With Recurrent Clostridium difficile Infection. Infect Control Hosp Epidemiol. 2016;38:196-202. DOI: 10.1017/ice.2016.246
4. U.S. Bureau of Labor Statistics. CPI Inflation Calculator. U.S. Bureau of Labor Statistics. Published 2022. https://www.bls.gov/data/inflation_calculator.htm. CPI inflation adjusted to March 2023.

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