The Food and Drug Administration (FDA) says its experts have not seen indications of safety problems from COVID-19 vaccine booster shots after European and international officials expressed concern about how repeat boosters may impact immune systems.

The FDA cleared boosters of the Moderna, Johnson & Johnson, and Pfizer vaccines for all adults late last year, and certain immunocompromised individuals can get a second booster under current U.S.

A top European Medicines Agency (EMA) official told reporters this week that no data yet exists to support giving more than one booster shot and repeat boosters would potentially lead to “problems with immune response.”.

Experts with the World Health Organization’s Technical Advisory Group, meanwhile, said in a brief around the same time as Cavaleri spoke that “a vaccination strategy based on repeated booster doses of the original vaccine composition is unlikely to be appropriate or sustainable.”.