There's mixed news from Pfizer on results from their CLOVER trial (CLOstridium difficile Vaccine Efficacy TRial), a phase 3 study involving 17,500 adults aged 50 and older that evaluated their candidate vaccine (PF-06425090) against Clostridioides difficile (C diff) for the prevention of C diff infection (CDI).
The bad news is that the trial didn't meet its efficacy endpoint — the prevention of primary CDI. According to a Pfizer press release, "Vaccine efficacy under the primary endpoint was 31% (96.4% CI -38.7, 66.6) following the third dose and 28.6% (96.4% CI -28.4, 61.0) following the second dose. For all CDI cases recorded at 14 days post dose 3, vaccine efficacy was 49%, 47% and 31% up to 12 months, 24 months and at final analysis, respectively."
(Medscape Medical News requested an interview with a Pfizer spokesperson, but the company declined to comment further.)
The good news is that the vaccine did meet its secondary endpoint. There were no cases of CDI requiring medical attention among vaccine recipients; by comparison, there were 11 cases among those who received placebo.
The Centers for Disease Control and Prevention classifies C diff with other antimicrobial resistance "threat" organisms, as the two often go hand in hand.
