Just before school started in the summer of 2017, Kids Plus Pediatrics of Pittsburgh posted a video on its Facebook page urging parents to vaccinate their children against human papillomavirus, or HPV, which can cause a variety of cancers. Three weeks later, communications director Chad Hermann noticed “something new happening” online.

First, someone posted the claim that “the vaccine kills.” Within minutes, more anti-vaccine comments came pouring in. The next day, someone inside a closed Facebook group started sending private messages with “screen shots so we could see them coordinating the attacks,” Hermann recalled.

Hermann would later discover that a woman in Australia was particularly active, directing people to give the practice negative reviews on various social media platforms. “She would say, 'Let’s move on to Yelp reviews,’ then change tactics and say, ‘Let’s go after the Facebook reviews,’ ” Hermann recalled.

Across the nation and around the world, pediatricians and other practitioners are increasingly coming under digital attack from a global movement that spreads misinformation about vaccines. Instead of enduring the abuse, Kids Plus fought back, tracking comments and turning its Facebook page data to researchers at the University of Pittsburgh.

What they found, in a study released Thursday in the journal Vaccine, is that most commenters weren’t from Pittsburgh at all but were from across the United States and around the world. Only five were from Pennsylvania. Within eight days, the page was flooded with 10,000 negative comments from about 800 commenters. Some messages were threatening, such as “You’ll burn in hell for killing babies.” Others were conspiratorial, such as “You have been brainwashed,” the doctors said.

Online attacks against people who speak out in favor of vaccines have become increasingly common, clinicians and vaccine advocates say. Social media websites are the primary platform for the anti-vaccination movement’s misleading claims. Although anti-vaccine activists are a small minority, on social media they may appear to be the majority.

What made this episode different is that the people at Kids Plus decided to investigate who was behind the attack and how it was carried out. The Pittsburgh practice worked with researchers from the University of Pittsburgh Center for Research on Media, Technology, and Health. Researchers analyzed a random sample of nearly 200 commenters to better understand the individuals behind the posts. They analyzed publicly available information that had been posted on each commenter’s Facebook page over two years to examine their social networks. That information included their political leanings and membership in other groups.

Their findings confirm previous research about those who are opposed or reluctant to vaccinate and the key arguments that resonate with them. Like many who are vaccine-hesitant or opposed to vaccines, the majority of commenters to the Pittsburgh practice were mothers. The top two political affiliations were on opposite ends of the political spectrum, with 56 percent expressing support for President Trump and 11 percent expressing support for Sen. Bernie Sanders, the researchers found.

Among the anti-vaccine themes in the comments were a mistrust of the scientific community, concerns about personal liberty, perceived risks about vaccine safety and the belief that government and pharmaceutical companies are part of a conspiracy to hide information.

Perhaps most significant, doctors and experts said, is that Kids Plus was able to figure out the social media attack was directed from inside closed anti-vaccine Facebook groups, in which members have to be approved to join. Together with the researchers’ analysis, the information provides the first systematic analysis of how anti-vaccine activists coordinate a harmful social media campaign, experts said.

“We know they’re all coordinated,” said Erica DeWald, director of advocacy for Vaccinate Your Family, the nation’s largest nonprofit dedicated to advocating for vaccinations. “But this is the actual research piece that proves that.”

Many health-care professionals are afraid of the impact anti-vaxxers can have on their business, according to DeWald. The online attacks often result in negative ratings and reviews on sites such as Google and Yelp.

“Quite frankly, it’s created a chilling effect,” she said. “If you’re a new parent trying to find the best provider for your child, because of these false or negative ratings, you could be missing out on finding a really great doctor or provider for your child.”

“This isn’t going away,” said Todd Wolynn, chief executive officer of Kids Plus Pediatrics, referring to online anti-vaccine attacks. “We didn’t want other groups to go through this,” he said. “We said, ‘Let’s learn from this.’ ”

Researchers said they did not see any evidence that the comments were posted by bots or trolls. All the profiles they analyzed appeared to be real individuals, said Beth Hoffman, a graduate student who led the research team. The accounts had histories going back many years, over a decade in some cases. There was also evidence that these real people were “checking in” to real places, having friends, and sharing pictures from real-life events, she said.

Kids Plus Pediatrics is a large practice that has about 20 clinicians and about 20,000 patients in Pittsburgh. On Aug. 23, 2017, the practice posted a video showing some of its providers talking about the importance of the HPV vaccine.

About three weeks later, Hermann started seeing the anti-vaccine comments flood in. Hermann said he banned 838 commenters in the first six days. Comments were not specific to the HPV vaccine. Commenters in the random sample were spread across 36 states and eight countries, including California, Texas, Oregon and Australia, where anti-vaccination sentiment is strong. Many of the attacks came from a small number of commenters, including some who were posting more than 100 times, Hermann said.

Researchers found many commenters consistently posted content on Facebook related to “naturalness,” and campaigned against circumcision and water fluoridation. But seemingly opposite groups “cling together on this issue of anti-vaccination,” said Brian Primack, the senior author who directs the university’s Center for Research on Media, Technology and Health. Other individuals expressed views that focused on liberty and potential government interference.

The pediatric practice said it is taking the information gleaned from the research to put together a primer for other physician practices and a pro-vaccine rapid-response network of physicians and others who will post pro-vaccine information to combat anti-vaccine social media campaigns.

“It will be like a virtual cavalry,” said Wolynn, the chief executive officer. “If somebody is under attack, these will help defend and fight off these attacks.”

Read more:

Anti-vaxxers face backlash as measles cases surge

Percentage of young U.S. children who don’t receive any vaccinations has quadrupled since 2001

The moral differences between pro- and anti-vaccine parents