Using tactics similar to those at work during the 2016 US presidential election, social media bots and Russian trolls promoted discord and spread false information about vaccines on Twitter, say researchers.
The team led by researchers from the George Washington University discovered several accounts, now known to belong to the same Russian trolls who interfered in the US election, as well as marketing and malware bots, tweeted about vaccines and skewed online health communications.
These Twitter accounts entered into vaccine debates months before election season was underway.
"It turns out that many anti-vaccine tweets come from accounts whose provenance is unclear. These might be bots, human users or 'cyborgs,' hacked accounts that are sometimes taken over by bots," said David Broniatowski, assistant professor in George Washington's School of Engineering and Applied Science.
The team, which also includes researchers from the University of Maryland and Johns Hopkins University, examined thousands of tweets sent between July 2014 and September 2017.
Dr Broniatowski's team reviewed more than 250 tweets about vaccination sent by accounts linked to the Internet Research Agency (IRA), a Russian government-backed company that interfered in the 2016 US elections.
The researchers found the tweets used polarising language linking vaccination to controversial issues in American society, such as racial and economic disparities.
"These trolls seem to be using vaccination as a wedge issue, promoting discord in American society," Mark Dredze, professor of computer science at Johns Hopkins University, said in a paper published in the American Journal of Public Health.
The researchers found that 'content polluters,' bot accounts that distribute malware, unsolicited commercial content and disruptive materials, shared anti-vaccination messages 75 per cent more than average Twitter users.
"Content polluters seem to use anti-vaccine messages as bait to entice their followers to click on advertisements and links to malicious websites," noted Sandra Crouse Quinn, professor from University of Maryland.
The findings suggest that a significant portion of the online discourse about vaccines may be generated by malicious actors with a range of hidden agendas, Broniatowski added.