Pfizer pauses vaccine trial
Pfizer and BioNTech halted a large US trial of their updated COVID vaccine for adults 50–64 because recruitment lagged, delaying new data on updated‑shot effectiveness and long‑term effects. The pause underscores falling trial demand and could push back timelines for evidence in older adults. (reuters.com)
Pfizer told trial investigators in a March 30 letter that it would stop active surveillance for COVID illness after April 3 and that enrollment for the U.S. study had been closed on March 6, with a target enrolment of roughly 25,000–30,000 participants. (usnews.com (usnews.com)) The ClinicalTrials.gov record for the study (NCT07300839) lists it as a Phase 3, randomized, double‑blind, placebo‑controlled trial that began Dec. 10, 2025 and aimed to enroll about 25,500 participants across more than 200 U.S. locations. (clinicaltrials.gov (clinicaltrials.gov)) Pfizer and BioNTech told Reuters that the study pause was not driven by safety or benefit‑risk concerns and that the companies informed the U.S. Food and Drug Administration of their intent to halt the study because of slow enrollment. (usnews.com (usnews.com)) Reuters reported the pause came after the FDA last year tightened requirements for broader use in healthy 50–64‑year‑olds by asking for large, placebo‑controlled trials for that age group, a shift that left no COVID vaccine approved for healthy adults 50–64 under the new guidance. (usnews.com (usnews.com)) Pfizer and BioNTech have continued to market an LP.8.1‑adapted formulation for older and high‑risk groups: Pfizer’s August 27, 2025 press release said the updated Comirnaty received FDA approval for adults 65+ and for ages 5–64 with underlying conditions. (pfizer.com (pfizer.com)) The trial’s ClinicalTrials.gov entry listed an estimated primary completion date of July 31, 2026, a milestone tied to the planned case‑count surveillance that the companies have said they could not generate because of slow enrollment. (clinicaltrials.gov (clinicaltrials.gov))
