(Bloomberg) -- Shares of vaccine makers plunged after President-elect Donald Trump nominated Robert F. Kennedy Jr. to run the Department of Health and Human Services, a post that would give the longtime vaccine skeptic influence over the nation’s health and medical research agencies.

Covid vaccine maker Moderna Inc. dropped 5.6% at the close of regular trading Thursday and lost an additional 1.4% post-market. Pfizer Inc. dropped 2.6% in regular trading while its Covid vaccine partner BioNTech SE sank 7%. Novavax Inc. dipped 7% at the close.

Kennedy has long been critical of immunizations, contending that they lack effectiveness and have links to autism, claims that have been repeatedly debunked. While he said last week that he wouldn’t take vaccines away from Americans, he assailed the science behind the shots’ safety, saying it “has huge deficits, and we’re going to make sure those scientific studies are done and that people can make informed choices.”

Kennedy will restore US regulators and public health agencies to “the traditions of Gold Standard Scientific Research,” Trump said in a statement on social media where he announced the nomination.

The prospect of Kennedy’s role in the next administration has alarmed public health officials who warned in recent days about the risks of curtailing vaccination efforts.

Vaccines are crucial to protecting children from deadly diseases, Centers for Disease Control and Prevention Director Mandy Cohen said Wednesday at the Milken Institute Future of Health Summit in Washington. “I don’t want to have to see us go backward in order to remind ourselves that vaccines work,” she said.