Facebook announced Thursday that it will reduce the visibility of groups and pages that "spread misinformation about vaccines" - and will reject advertisements that "include misinformation about vaccines."

How This Will Work Leading global health organizations, such as the World Health Organization and the US Centers for Disease Control and Prevention, have publicly identified verifiable vaccine hoaxes. If these vaccine hoaxes appear on Facebook, we will take action against them. For example, if a group or Page admin posts this vaccine misinformation, we will exclude the entire group or Page from recommendations, reduce these groups and Pages’ distribution in News Feed and Search, and reject ads with this misinformation. -Facebook

The announcement comes after weeks of public pressure from lawmakers, including Reps. Adam Schiff (D-CA) and Michael Burgess (R-TX), who introduced a bipartisan resolution this week to reject "unfounded and debunked theories" about vaccines.

"We are exploring ways to share educational information about vaccines when people come across misinformation on this topic," reads Facebook's announcement, which adds that "Leading global health organizations, such as the World Health Organization and the US Centers for Disease Control and Prevention, have publicly identified verifiable vaccine hoaxes. If these vaccine hoaxes appear on Facebook, we will take action against them."

Last month, Rep. Schiff sent a letter to Facebook CEO Mark Zuckerberg and Google CEO Sundar Pichai following a January measles outbreak in the Pacific Northwest, outlining his concerns with the way Silicon Valley tech giants are dealing with anti-vaccine content.

"As a Member of Congress who is deeply concerned about declining vaccination rates, I am requesting additional information on the steps that you currently take to provide medically accurate information on vaccinations to your users, and to encourage you to consider additional steps you can take to address this growing problem," wrote Schiff, noting that YouTube had recently announced that it would not longer recommend videos that promote "vaccine misinformation."

Facebook responded to Schiff's letter by saying it was "working on additional changes" to "reduce the distribution of health-related misinformation."

According to BuzzFeed, the company will use machine-learning and manual human review to target anti-vaccine information, such as content promoting links to autism.

One of the most popular and prolific Facebook communities for anti-vaxxers is called "Stop Mandatory Vaccination," run by Larry Cook, the former executive director of the California Naturopathic Doctors Association. Over the past month, YouTube has demonetized Cook’s videos and his books appear to be recommended less on Amazon. The public Stop Mandatory Vaccination and its adjacent private group are two of the larger spaces for anti-vaxxers on Facebook and the recommendation widgets that appear on the sidebar when you visit them serve as a vector to promote similar communities. -BuzzFeed

Facebook's anti-vax crackdown will extend to Instagram, where anti-vax hashtags will no longer populate on Instagram hashtag pages. They will also be blocked from Instagram's explore tab.