A measles outbreak spanning multiple states is nearing 600 cases, and experts say it might just be the beginning.

Many people not getting tested for measles or don't have access to test for highly infectious disease as outbreak area expands.

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.

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,

Robert F. Kennedy Jr.’s response to the outbreak has drawn criticism from both serious scientists and his most loyal supporters.