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

The Food and Drug Administration has issued a long-awaited approval of Novavax’s COVID-19 vaccine but with unusual restrictions. Novavax makes the nation’s only traditional protein-based coronavirus vaccine – and until now it had emergency authorization from FDA for use in anyone 12 and older.