Bots and Russian trolls spread misinformation about vaccines on Twitter to sow division and distribute malicious content before and during the American presidential election, according to a new study. Scientists at George Washington University, in Washington DC, made the discovery while trying to improve social media communications for public health workers, researchers said. Instead, they found trolls and bots skewing online debate and upending consensus about vaccine safety. The study 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, tweeting about vaccines. Russian trolls played both sides, the researchers said, tweeting pro- and anti-vaccine content in a politically charged context. “These trolls seem to be using vaccination as a wedge issue, promoting discord in American society,” Mark Dredze, a team member and professor of computer science at Johns Hopkins, which was also involved in the study, said.