The 2015 Disneyland measles outbreak was a pivotal moment in explaining the vaccine hesitation we see today. The outbreak made clear that number of people opting out of vaccination was significant. But it also changed the people protesting vaccines. Before that, activists speaking out about vaccines had mainly been parents concerned about the safety of their kids. California's push to get rid of vaccine exemptions in the wake of the outbreak changed the conversation. It became political. It became about choice and freedom and democracy.