Two weeks ago, by inserting what must be the most notorious asterisk in modern public health, the Centers for Disease Control and Prevention caveated its long-standing position that vaccines do not cause autism. Under the direction of Robert F. Kennedy, Jr., the Secretary of Health and Human Services, a C.D.C. web page now contends that this is “not an evidence-based claim” and that research linking vaccines to autism has been “ignored by health authorities.”