Formally permitting third shots will allow the government to study the effects of extra doses. “I hope it shows evidence that a booster shot is working for this group,” said [Professor] Philip Felgner, who directs the Vaccine Research and Development Center at the University of California, Irvine.
Who should get a third COVID-19 vaccine shot? About 2.7M immunocompromised Americans, CDC says
USA Today, Aug. 13, 2021
August 13, 2021