NEW YORK (AP) — Like health officials facing measles outbreaks, internet companies are trying to contain vaccine-related misinformation they have long helped spread. So far, their efforts at quarantine are falling short.

The digital scrapbooking site Pinterest—which has been a leading online repository of vaccine misinformation—in 2017 took the seemingly drastic step of blocking all searches for the term “vaccines,” affecting even legitimate searches for information. It was part of the company’s enforcement of a broader policy against health misinformation.

But it’s been a leaky quarantine. Recently, a search for “measles vaccine” still brought up, among other things, a post titled “Why We Said NO to the Measles Vaccine,” along with a sinister-looking illustration of a hand holding an enormous needle titled “Vaccine-nation: poisoning the population one shot at a time.” Search results for “vaccine safety” and “flu vaccine” can turn up posts with scientifically debunked information.

Facebook, meanwhile, said in March it will no longer recommend groups and pages that spread hoaxes about vaccines—and that it will reject ads that do this.

This appears to have filtered out some of the most blatant sources of vaccine misinformation, such as the website Naturalnews.com, which had regularly posted anti-vaccine propaganda and showed up high in Facebook searches about the topic.

But even after the changes, groups—such as one with 197 members and more than 10 posts a day seeking to “discuss the dangers of vaccination” was among the first results for a search on “vaccine safety.” A more generic “vaccine” search, meanwhile, turns up the verified profile of Dr. Christiane Northrup, a high-profile physician who’s outspoken about her misgivings about—and at times opposition to—vaccines. On Facebook’s Instagram, hashtags such as “vaccineskill” and accounts against vaccinating children are easily found with a simple search for “vaccines.”

Anti-Vax: Past And Present

In social media’s battle against misinformation, bogus claims about the dangers of vaccines are the next target. With some dangerous childhood diseases making a comeback due to lower vaccination rates, Facebook, Pinterest and others are trying to put the genie back in the bottle, even as they are hesitant to acknowledge responsibility for spreading falsehoods.

“There has been hesitancy about vaccines as long as vaccines have existed,” said Jeanine Guidry, professor at Virginia Commonwealth University who studies social media and vaccines. Such sentiment, dating back to the 1700s, was once confined to towns and local communities. Online, it dates back long before Facebook and Twitter. A 2002 study on Google search results found that 43% of the sites surfaced after searches for “vaccination” and “immunization” were anti-vax.

Still, experts in online misinformation say the impact of social networking and its unfiltered, algorithmically boosted dissemination of the most “engaging” posts—whether true or not—have fueled a much broader spread of anti-vaccination propaganda. Richard Carpiano, a professor of public policy and sociology at the University of California, Riverside, who studies vaccine trends, said there is a “disproportionate” number of websites on the topic with misinformation, peddled by “anti-vax activists” and parent bloggers. Researchers have even found Russia-linked bots trying to sow discord by amplifying both sides of the vaccine debate.

“It’s completely understandable why parents would seek out this stuff,” he said. The problem is, they spend a lot more online than they do in a doctor’s office where they are much more likely to receive accurate information.

The bogus notion that vaccines cause autism—kicked off by a now disproven study from 1998—didn’t start on social networks but it has certainly spread there.

Health care officials and experts worry about the echo chambers of misinformation on social media that have become prevalent in the past decade and their role in pushing parents who are on the fence into the anti-vax camp.

Sharing Misinformation

While headlines in the past two years have largely focused on fake political news proliferating on Facebook, Twitter and Instagram, large swaths of people (along with bots) are also sharing concerns and bogus “research” about the perceived dangers of vaccinating children.

Guidry said social media amplifies these conversations and makes it easier for people to have such conversations in echo chambers that can reinforce misinformation. Her research found that that Pinterest—popular with women—has been especially susceptible to vaccine falsehoods. Nearly 75% of vaccine-related “pins” (the visual posts on the service) were against immunization in her 2015 study, compared with roughly a quarter on Twitter (based on another study). While Pinterest has strengthened its systems against such posts since, Guidry notes that stuff still gets through the filters.

Misinformation on Facebook is more difficult to study since a lot of it isn’t public, especially when people post in hidden or secret groups—where much of the hoaxes and false claims are spread. In such groups, like-minded people congregate to share their views and receive support from their peers. Facebook’s new policies mean fewer people will find those groups, but the company is not going so far as banning them altogether.

Carpiano said it is difficult to study the actual impact social media has had on vaccine uptake, but “we do see decrease in coverage and rise in gaps of coverage,” as well as the clustering of vaccine-hesitant people. This, he said, has correlated with the rise of lots of different sources of information people now have at their fingertips. Despite high-profile outbreaks, overall vaccination rates remain high in the U.S. according to the Centers for Disease Control. But the percentage of kids under 2 who haven’t received any vaccines is growing.

The Trajectory Of Fake News

Fake news about health and medicine often follows a similar trajectory as fake news about politics. Some of it is for financial gain, some is intended to wreak havoc in the public discourse, some is spread by people who might genuinely believe it. InfoWars, the conspiracy site run by Alex Jones, routinely pushes anti-vax agenda and stories of “forced inoculations,” even as it peddles bottles of “Survival Shield” iodine. Natural News, meanwhile, has built a business on unproven health claims and selling $29 jars of “organic apple peel powder.”

Carpiano noted that even with anti-vaccination activists getting a large share of the public’s attention, much more common are parents who are merely hesitant or concerned about immunization. Understandably, they seek out information—and a lot of what they find is false.

“It is a misinformation campaign,” he said. “Often couched in ‘oh we are for choice, understanding, education,’” he said. “But fundamentally it is not open to scientific debate.” •