He also fueled long-debunked claims that ingredients in vaccines or timing shots close together could contribute to rising rates of autism in the U.S., without providing any medical evidence. One challenge is that it’s hard to disentangle the effects of Tylenol use from the effects of high fevers during pregnancy. Trump also urged not giving Tylenol to young children, but scientists say that research indicates autism develops in the fetal brain. The theory is that some, not all, children with autism may not properly metabolize folate, Mandell said. Though anti-vaccine activists, including Kennedy, have long suggested a link between vaccines and autism, widespread scientific consensus and decades of studies have firmly concluded there isn’t one.