The United States is in the midst of containing the largest number of measles cases in 25 years. Measles, a vaccine-preventable disease, was eliminated from the US in 2000, but the spread of online misinformation about vaccines has led to a public health crisis that has resulted in more than 800 cases in at least 20 states. Vaccine sceptics represent only a tiny minority of the population, but their digital advocacy has evolved into the "anti-vaccine" movement - a well-organised online network with significant offline implications for public health and politics. These groups promote medically inaccurate information about vaccines and their viral content has dominated US's most powerful online platforms, including Facebook, Google, Amazon and YouTube. Ill-equipped to respond to the social media savvy anti-vax movement, the US medical community must now confront both the contagion of online misinformation and the real-world viral spread of vaccine-preventable diseases. In this episode, Fault Lines travelled to Washington state, as it was in the midst of containing an outbreak, to speak with public health officials and community members battling on the front lines of the measles crises while waging online "info-wars" against the anti-vaccine movement's misinformation. Fault Lines then went inside the US's anti-vaccine movement, interviewing key leaders about their online strategy and offline political goals, as well as the threat that fear and misinformation can pose to public health in the US.