After a six-week delay, the US Food and Drug Administration has approved Novavax’s Covid-19 vaccine, according to a letter from the agency, but only for people 65 and older and those 12 and up who have at least one underlying condition that puts them at higher risk of severe illness.

The notice came shortly after an advisory panel meeting at which members debated the pros and cons of asking manufacturers to update their vaccines.

The agency narrowed who can get the shot and added new study requirements that could cost the company tens of millions.