We are away for Christmas, so this is a repeat of a previous episode.

In September, President Trump and the U.S. Health Secretary Robert F. Kennedy Jr. held a press conference in which they made extraordinary new claims about autism. They suggested a potential link between the use of Tylenol during pregnancy and the development of autism. They also advocated spacing out childhood vaccinations.

The two men's interest in the link between vaccines and autism goes back decades but these claims did not originate in the US. They trace back to the UK in 1998, when disgraced former doctor Andrew Wakefield first published his now-debunked theory linking MMR vaccines to autism cases in children.

The science journalist Adam Rutherford explains to the Global Story how the Wakefield vaccine conspiracy became the biggest medical disinformation disaster in recent history, and how these ideas found fertile ground in the Trump administration.

Producers: Viv Jones, Valerio Esposito

Executive producer: Annie Brown, James Shield

Mix: Travis Evans

Senior news editor: China Collins

Photo: President Trump & Robert F. Kennedy Jr. Kevin Lamarque/Reuters