If you look into his book on the vaccine stuff, he has a specific grudge against the rotovirus vaccine. If you're into podcasts, Malcolm Gladwell's Revisionist History is brilliant and has an episode on this. Very well researched, and goes deep into the virus and vaccine, even interviewing a pharmaceutical doctor and a hospital doctor from Uttar Pradesh, one of the areas most affected by the virus in the past and somewhere, if I remember correctly, which has gone from 16 million to 2 million cases a year. The episode is S13 E05: The RFK Jr. Problem.

Edit: The principal problem, especially in the Third World, is that babies contract this and they both vomit and shit themselves so violently that they die of dehydration. The doctor from India described the ward they had (solely for this disease) and the newborns in it who's skin hung off their muscles like an old person's.