Shares of major vaccine companies fell Thursday after President-elect Donald Trump nominated Robert F. Kennedy Jr., a well-known vaccine skeptic, to lead the Department of Health and Human Services. The stocks of Moderna, Novavax, Pfizer, and BioNTech declined sharply, as reports emerged of Kennedy's nomination. Experts warn a second Trump term could amplify Kennedy's anti-vaccine stance, potentially discouraging Covid and routine vaccinations that have historically prevented severe illnesses and saved lives.