Novavax shares jumped more than 15% on Monday after the company secured a long-awaited U.S. regulatory approval for its COVID-19 vaccine, albeit with new conditions, which helped allay some investor concerns over the future of the shot.

Novavax Inc. jumped after US regulators fully approved its Covid vaccine, easing investors’ concerns after the clearance was delayed and US Health and Human Services Secretary Robert F. Kennedy Jr. raised doubts about its efficacy.

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.