When Robert F. Kennedy Jr. was appointed secretary of Health and Human Services, some hoped that the responsibility of public office would temper his long-standing hostility toward vaccines. Instead, he is doing exactly what many of us feared: dismantling the systems that protect Americans from preventable infectious diseases.

Kennedy Jr. poses a direct threat to American health. Far from restoring trust—Kennedy’s stated aim—this action dismantles a process that was a model for the world, built over six decades, and will create confusion for doctors,