On Sunday, Robert F. Kennedy Jr. met with the families of two girls who had died from measles in West Texas—and raised doubts about the safety of vaccines. “He said, ‘You don’t know what’s in the vaccine anymore,’” Peter Hildebrand, whose 8-year-old daughter Daisy’s funeral had been held just hours earlier, told me. “I actually asked him about it.”

Shares of vaccine makers fell after US Health and Human Services Secretary Robert F. Kennedy Jr. raised doubts about the efficacy of a certain type of Covid vaccine.

Health secretary Robert F. Kennedy Jr. this week is sowing doubt about the safety and efficacy of some vaccines — beyond the measles shot — and arguing the government shouldn’t mandate their use.