This study analyzes the impact of COVID-19 deniers on the spread of COVID-19 in Germany. In a rst step, we establish a link between regional proxies of COVID-19 deniers and infection rates. We then estimate the causal impact of large anti-lockdown protests on the spread of COVID-19 using an event study framework. Employing novel data on bus stops of travel companies specialized in driving protesters to these gatherings, and exploiting the timing of two large-scale demonstrations in November 2020, we nd sizable increases in infection rates in protesters’ origin regions after these demonstrations. Individual-level evidence supports the main results by documenting that COVID-19 deniers engage less in health protection behavior. Our results contribute to the debate about the public health costs of individual behavior that has detrimental externalities for the society.