Sen. Bernie Sanders accused Kennedy of praising Andrew Wakefield, the primary author of a now-debunked paper from the U.K. in 1998, which allegedly found that MMR vaccines cause autism.
The paper has since been discredited by health experts and retracted from the journal in which it was published.
In February 2004, The Sunday Times published an investigation, accusing Wakefield of a conflict of interest.
It alleged some of the parents of the children in the paper were suing vaccine manufacturers prior to its publication and Wakefield had received funding to try to find a link between the MMR vaccine and autism, which was not disclosed in the Lancet article. This led to 10 of the 13 authors withdrawing their support.
In 2010, Wakefield lost his medical license after the paper was discredited and an investigation found he had acted "dishonestly and irresponsibly" in conducting his research. More than a dozen high-quality studies have since found no evidence of a link between childhood vaccines and autism.