The ads appear to violate Facebook policies that ban ads with claims debunked either by outside fact checking teams or "organizations with particular expertise," including anti-vaccination content. In the case of these ads, the World Health Organization would be one of those groups. Earthley also promotes anti-vaccination myths through its public accounts and groups, although Facebook already tends to downplay this content.

However, Facebook disagrees with that interpretation. A spokesperson said the ads represented "no violation" of its policies, and the social network was still running the ads as of this writing. It didn't tell Engadget why it believed the ads were acceptable.

The presence of the ads highlights both the limitations of Facebook's ad policies (including its willingness to let politicians lie) as well as the challenges of stopping bogus claims. It doesn't take much for an ad to avoid Facebook's ban on anti-vaccination ads, even when it's clearly violating the spirit of that ban. And no matter how stringent Facebook's policies are, there may be only so much it can do. It can't possibly guess every possible anti-vaccination hashtag, as BuzzFeed observed. It's just a question of whether Facebook's approach is thorough enough to tackle problems like this.