As a measles outbreak spread through Lancaster county, Pennsylvania, in August, a parent turned to a massive public Facebook group, Crunchy Moms, for advice. The parent was considering getting their three-year-old vaccinated, in part to protect their six-month-old.

“I’m nervous for my baby,” the parent wrote.

“First of all your children cannot die of measles. It is literally impossible,” one member responded. “Do not do it,” advised another. Others said the vaccine would spread measles or that it would be like “injecting poison”.