Overview
- Pfizer and BioNTech said Wednesday they halted recruitment in a U.S. efficacy study for healthy adults 50 to 64 after falling well short of volunteer targets.
- A letter to investigators dated March 30 said symptom tracking for all participants will end after April 3, following a March 6 decision to close enrollment.
- The trial, conducted as an FDA post‑marketing commitment, sought roughly 25,000 to 30,000 people, and the companies said the move was not related to safety concerns.
- Sites pointed to new FDA guidance that calls for large placebo‑controlled trials and to strict health screens that exclude common conditions like hypertension, with one contract research firm estimating over 80% of applicants fail pre‑screening.
- Moderna is still running a similar 30,000‑person U.S. study that sites say is also hard to enroll, and experts warn the FDA’s May vaccine meeting may lack data for this age group as booster uptake has dropped to about 18%.