Kennedy, then a prominent anti-vaccine activist, preceded the 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.

Kennedy’s Samoa visit has become one of the most contentious events in his career. At the time, he was leading a nonprofit known for its anti-vaccine activism. Critics said the visit fueled anti-vaccine sentiment in Samoa, which later experienced the measles outbreak that killed 83 people, mostly children under 5.