Facebook says it has removed 12 million pieces of content on its namesake app and Instagram for violating its rules on misinformation that could lead to “imminent physical harm.” | Chris J. Ratcliffe/Getty Images

Facebook critics say the anti-vaccination communities that have flourished on the platform are fueling Covid-19 vaccine hesitancy.

After years of allowing anti-vaccine groups and pages to rack up followers on its social network, Facebook announced last month that it wants to lead the world’s largest Covid-19 inoculation information campaign and encourage its users to get vaccinated. It’s also banned users from sharing general forms of vaccine misinformation, like the idea that vaccinations cause autism.

Facebook’s big push is meant to help bring an end to a pandemic that has killed more than 2.5 million people around the world. But for some of