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
