Social media sites like YouTube are stepping up their enforcement against anti-vax content.

YouTube channels that promote anti-vaccination content are not allowed to run ads on the video sharing platform, according to a policy first reported by BuzzFeed News on Friday.

YouTube said that it considers anti-vaccination content to be "dangerous or harmful," which as a policy, it does not allow to be monetized- meaning that it won't allow the video to generate any money for the creator from advertising.

"We have strict policies that govern what videos we allow ads to appear on, and videos that promote anti-vaccination content are a violation of those policies. We enforce these policies vigorously, and if we find a video that violates them, we immediately take action and remove ads," a YouTube spokesperson told Business Insider in a statement.

YouTube told us that restricting ads for anti-vaccination videos is not a new policy for the company. However, at least a few channels were able to monetise, in violation of this policy, according to BuzzFeed News.

According to the BuzzFeed News report, several channels promoting the anti-vaccine content – including VAXXED TV, LarryCook333, and iHealthTub – were able to run ads, unbeknownst to the advertisers themselves.

Several companies reportedly asked YouTube to stop their ads from being placed on the videos, while one – a discount vitamin company called Vitacost – pulled their ads from YouTube entirely, according to the report.

YouTube has since prevented all three channels from running ads, after BuzzFeed News brought the matter to the company's intention.

Social media platforms, including Facebook and YouTube, have been used aggressively by anti-vaccination proponents. Pinterest, meanwhile,blocked searches for anti-vaccine content from its service earlier this week.

This all comes even as outbreaks of measles have spiked this year. Since January, there have been over 120 instances of measles, according to the Centres for Disease Control and Prevention (CDC). That's more than the entire year of 2016, when there were only 86.

California Congressman Adam Schiff sent a letter to Google CEO Sundar Pichai and Facebook CEO Mark Zuckerburg last week expressing concern over the information on both companies' sites that "discourages parents from vaccinating their children, contributing to declining vaccination rates which could reverse progress made in tackling vaccine-preventable diseases."

This article was originally published by Business Insider.

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