In March 2019, a teenager from Ohio, Ethan Lindenberger, sat before a Senate Committee in Washington. Wearing glasses, a suit and tie, his hair carefully combed to the side, he described how his mother refused to vaccinate him. Her beliefs, which he began challenging aged 13, were reinforced by conspiracy theories she found online. “My mother would turn to anti-vaccine groups and social media looking for evidence in her defense,” he told the committee.

The Senate hearing had been called to examine the reasons behind the recent resurgence of preventable diseases. Across the United States, American physicians are battling the worst measles outbreaks in decades. And globally, polio – which had almost been on the brink of extinction – is making a deadly comeback. 

Responding to mounting pressure in the wake of Lindenberger’s speech, Facebook pledged to stop recommending vaccine disinformation on its platforms and make it harder to find anti-vax content in searches. But eight months on, evidence gathered by Coda shows that anti-vaxxer movement is flocking to Facebook-owned Instagram, gaming the app’s algorithm to spread anti-vaccine disinformation.

Until the spring of this year, anti-vaxxers enjoyed near total freedom on Instagram. “They had a white flag where they could do anything they wanted,” said Anne-Julie Dionne, 22, a Quebec-based pro-vaccine campaigner who runs an account called @queenofvaccines.