Abstract: Vaccines are responsible for large increases in human welfare and yet we know little about the political impacts of publicly-managed vaccination campaigns. We fill this gap by studying the case of Chile, which offers a rare combination of a high-stakes election, voluntary voting, and a vaccination process halfway implemented by election day. Crucially, the roll-out of vaccines relied on exogenous eligibility rules which we combine with a pre-analysis plan for causal identification. We find that higher vaccination rates boost political participation and empower challengers irrespective of their party affiliation. Survey evidence suggests that vaccines could have increased preferences for challengers by lowering decision-related anxiety. Keywords: vaccines, politics, election, challengers.