Seres Therapeutics, Inc. announced the publication in the New England Journal of Medicine (NEJM) of data from its Phase 3 ECOSPOR III study evaluating SER-109, an investigational oral microbiome therapeutic for the treatment of recurrent C. difficile infection (rCDI). The publication highlights data that found SER-109 to be superior to placebo in reducing CDI recurrence, with 88% of SER-109 patients achieving a sustained clinical response compared to 60% on placebo. SER-109 was also found to be well tolerated, with a side effect profile comparable to placebo and no serious drug-related adverse events observed.

Seres expects to finalize a BLA submission for SER-109 with the U.S. Food and Drug Administration (FDA) in mid-2022. The SER-109 ECOSPOR III Phase 3 study (ClinicalTrials.gov identifier: NCT03183128) was a multicenter, randomized, placebo-controlled study. Previously reported topline data demonstrated that the study achieved its primary endpoint where SER-109 was superior to placebo in reducing CDI recurrence at eight weeks, reflecting a sustained clinical response rate of approximately 88% at eight weeks post-treatment.

SER-109 resulted in a 27% absolute reduction of recurrence of CDI compared to placebo at eight weeks post-treatment, which is a relative risk reduction of 68%. In May 2021, Seres presented 24-week clinical data from the study that demonstrated significantly reduced recurrence rates compared to placebo.