YouTube channels pushing anti-vaccination conspiracy theories will no longer get money from adverts, as YouTube pulled the plug on serving ads to popular channels that promote anti-vax views.
YouTube's decision is believed to have been prompted by complaints from large advertisers, including Hasbro, Nestle, AT&T, Kellogg, Epic Games and others, who did not want their content playing alongside videos promoting such views.
Some companies are believed to have pulled all their advertising until YouTube took action.
The World Health Organization said anti-vaccine views were a "top 10 global health threat" in 2019.
In January by Prof Dame Sally Davies, the UK's chief medical officer, criticised social media for fuelling vaccine fears. She said that myths about the dangers of vaccines on social media was one reason parents weren't taking their children to get the MMR vaccine.
"A number of people, stars, believe these myths - they are wrong,” Dame Sally said.
YouTube said it was also trying to make legitimate vaccination content easier to find, and was also stopping anti-vaccine videos appearing in recommendation lists.
It said it was also planning to create "information panels" on pages that listed sources where people can fact-check information for themselves.