Pfizer, BioNTech halt US COVID vaccine study after recruitment struggles

Vaccine makers Pfizer PFE.N and BioNTech 22UAy.DE halted a large U.S. trial of their updated COVID-19 vaccine in healthy adults aged 50 to 64, saying enrollment in the trials had been too low to generate the needed data.

In a letter to trial investigators dated March 30, seen by Reuters and previously unreported, Pfizer said it would stop surveillance for signs of COVID illness of all participants in the study after April 3.

Enrollment was closed on March 6, following a review of current epidemiological trends, it said.