Many YouTube channels pushing anti-vaccination conspiracy theories will no longer get money from adverts.
On Friday, YouTube stopped serving ads to lots of popular channels that promote such views.
It took the step following protests from firms who discovered their adverts were running alongside the controversial videos.
The World Health Organization said anti-vaccine views were a "top 10 global health threat" in 2019.
The video-sharing site said it took the step because many of the anti-vaccine channels were promoting "harmful or dangerous " views.
"Any misinformation on medical topics is especially concerning," it said in a statement.
Alongside the decision to remove ads, it said it was also trying to make "more authoritative content" easier to find on the benefits of vaccination and was also stopping anti-vaccine videos appearing in recommendation lists.
It was also planning to create "information panels" on pages that listed sources where people can fact-check information for themselves.
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