Shares of vaccine makers fell Thursday as President-elect Donald Trump nominated Robert F. Kennedy Jr., a prominent vaccine skeptic, to lead the Department of Health and Human Services. 

The stocks fell in the final hour of trading as reports emerged about Trump’s expected pick. Moderna‘s stock closed more than 5% lower on Thursday, shares of Novavax fell more than 7% and Pfizer‘s stock ended more than 2% lower.

Shares of BioNTech, the German drugmaker that helped develop a Covid vaccine with Pfizer, closed more than 6% lower. British drugmaker GSK, which makes flu shots and several other vaccines, closed roughly 2% lower.

Shares of those companies dipped further in extended trading as Trump confirmed his pick in a post on his platform Truth Social.

Health policy experts have said a second Trump term could allow Kennedy to elevate anti-vaccine rhetoric, which could deter more Americans from receiving Covid shots and routine immunizations that have for decades saved millions of lives and prevented debilitating illnesses.

Pfizer, Moderna and Novavax are still recovering from falling Covid vaccination rates in the U.S., which have dented their profits over the past two years. 

Kennedy’s track record as a vaccine skeptic is extensive. He has long made misleading and false statements about the safety of shots, such as claiming they are linked to autism despite numerous studies going back decades that debunk the association.

Kennedy is the founder of the nonprofit Children’s Health Defense, the most well-funded anti-vaccine organization in the country.