John Wherry of the Perelman School of Medicine said the existing COVID-19 vaccines appear to be holding up, even without booster shots. “Severe infections, hospitalizations and deaths are being observed almost entirely in unvaccinated populations, even for the delta variant,” he said.
https://www.technologyreview.com/2021/07/15/1028803/pfizer-wants-to-give-you-a-booster-shot-but-experts-say-its-too-soon/ MIT Technology Review