Newly obtained documents indicate that the US health secretary, Robert F Kennedy Jr, lied during two congressional hearings last year, when he told lawmakers who held the key to his confirmation that a 2019 visit to Samoa had “nothing to do with vaccines”.

Letters obtained by the Guardian and the Associated Press contradict that testimony. In one he wrote to the Samoan prime minister before the trip, Kennedy explicitly said he wanted to study the measles, mumps and rubella vaccine in the Pacific island nation. In it, he used the words vaccine or vaccination eight times.

“I am writing this letter to you in the hope that we might be helpful to the people of your great nation,” he wrote, adding that he believed the deaths of two children there after an MMR vaccine could have resulted from manufacturing issues.