The U.S. Senate Finance Committee has voted to advance Robert F. Kennedy Jr.’s nomination for Secretary of Health and Human Services to the full Senate. Shares in Moderna (NASDAQ:MRNA) and BioNTech (NASDAQ:BNTX) slumped on the news: Moderna was down 4.9% and BioNTech 1.5%.

The fall in stock prices comes from concerns about Kennedy’s views on vaccines. He has been a prominent figure in the anti-vaccine movement. Despite denying the label of an anti-vaxxers, he has raised doubts about the safety and efficacy of vaccines. His potential confirmation as the head of the department that oversees healthcare programs and the Food and Drug Administration (FDA) has made investors in vaccine manufacturers worried.

If his appointment is confirmed by the Senate, it would put the future of U.S. vaccine policy in doubt. Kennedy would be responsible for an agency that manages more than $3 trillion in healthcare spending and provides health insurance to over 140 million Americans.

The market’s response to the news reflects investor apprehension and concerns over possible changes in vaccine policies and regulations, which could have a big effect on the operations and revenue of these companies.