Here's a timeline of how federal public health officials went from offering Pennsylvanians their condolences to questioning whether the deaths occurred.

Medical experts say the brouhaha has diverted focus from an exploding public health threat.

Robert F. Kennedy Jr., then a prominent anti-vaccine activist, preempted the 2019 visit with a letter to the Samoan prime minister requesting to study the Pacific island nation's measles, mumps and rubella vaccines after the deaths of two children who had received them. In the letter, he used the words vaccine or vaccination eight times.