Groups opposing vaccines are small in size, but their online-communications strategy is worryingly effective and far-reaching, a report from Johnson’s team suggests. Before the SARS-CoV-2 virus emerged, Johnson’s team began mapping out a network of views on vaccination, on Facebook. They investigated more than 1,300 pages, followed by about 85 million individuals.

Their findings1, published on 13 May, suggest that anti-vaccination pages tend to have fewer followers but are more numerous than pro-vaccination ones, and are more often linked to in discussions on other Facebook pages — such as parent associations at schools — whose stance on vaccination is undecided.

In contrast, pages that explain the benefits of and the scientific case for vaccination are linked in a network that is largely disconnected from this “main battlefield” for public sentiment, as Johnson puts it. During measles outbreaks in 2019, anti-vaccination pages grew more links than did pro-vaccination ones on Facebook, Johnson’s team adds. An extrapolation of current trends using computer simulations suggests that opposition to vaccines might dominate the network of views on vaccines within ten years, they write.