Confronting the evolution and expansion of anti-vaccine activism in the USA in the COVID-19 era.

Over the past two decades, anti-vaccine activism in the USA has evolved from a fringe subculture into an increasingly well organised, networked movement with important repercussions for public health. The COVID-19 pandemic has exacerbated this evolution and magnified the reach of vaccine misinformation. Anti-vaccine activists, who for many years spoke primarily to niche communities hesitant about childhood vaccinations, have used traditional and social media to amplify vaccine-related mistruths about COVID-19 vaccines while also targeting historically marginalised racial and ethnic communities.