Moderna CEO Stephane Bancel on Thursday said the efficacy of boosters against COVID-19 will likely decline over time, and people may need a fourth shot later this year to increase their protection.

Bancel said people who received their boosters last fall will likely have enough protection to get them through the current winter season and the accompanying surge in infections.

He says some governments, including the U.K. and South Korea, are already ordering the doses in preparation. “I still believe we’re going to need boosters in the fall of ’22 and forward,” Bancel said.