The Information Ecosystem of Online Groups with Anti- and Pro-vaccine Views on Facebook.

There has been growing concern about public distrust in science (1-3). Opposition and hesitancy to vaccination have been one of the major threats to global health (4-6). Social media sites have been suspected as a breeding ground of misleading and unsubstantiated narratives about vaccines (5, 7-10), but little is known about how pervasive anti-vaccine views on the world's largest social media, Facebook, and how online groups produce their false narratives. Here, we study the prevalence and characteristics of online groups with anti- and pro-vaccine views on Facebook by analyzing 2,328 Facebook pages and groups and over 1.6 million posts created by them between 2012 and 2020. We found that anti-vaccine views have been dominant on the platform in terms of the number of groups and the volume of content they generated. Analyses of online information sources that enabled the production of vaccine narratives revealed that vaccine content using low credibility sources was less than 2%, and anti-vaccine groups have increasingly more utilized other relatively credible sources, such as government sources and legitimate news media. It was also found that nearly 20% of sources used by anti-vaccine groups each month were not shared by any pro-vaccine groups, and sources that were more widely used among anti-vaccine groups tended to represent more conservative and far-right political beliefs. The findings suggest that extensive and targeted interventions are urgently needed to suppress anti-vaccine groups on social media.