Social media companies face increasing scrutiny for amplifying fringe anti-vaccine sentiment amid measles outbreaks in several states like Washington. In response, Facebook, YouTube and Pinterest recently made headlines by announcing initiatives to reduce vaccine misinformation on their platforms.

But the focus on anti-vaccine content on social media can obscure the most important factor in whether children get vaccinated: the rules in their home states, which are being revisited in legislative debates across the country that have received far less attention.

A teenager testified before Congress on Tuesday that he got vaccinated in defiance of his mother, who he said got her anti-vaccination views from social media. Although this kind of misinformation can endanger public health, it’s not obvious that social media is substantially increasing overall vaccine hesitancy. Despite rapid growth in the proportion of Americans using social media sites, flu vaccination rates and infant immunization levels have largely remained stable in recent years. Moreover, fears about and resistance to vaccination are not new; they date to the late 18th century, when the first vaccine was developed.