Monetary incentives for vaccination may undermine intrinsic motivation, but evidence on this effect remains scarce. We conducted an experiment among 513 vaccine-hesitant adults to test whether priming individuals with a monetary incentive reduces their willingness to vaccinate against COVID-19. California Health Interview Survey (CHIS) responses were used to benchmark the sample in this experiment. 

Findings: One in seven were willing to vaccinate without an incentive but declined the vaccine when asked to consider a payment. Additionally, priming participants lowered their perceptions of vaccine safety by 9 pp and prosocial attitudes toward vaccination by 10 pp. These negative effects were concentrated among men, racial and ethnic minorities, and participants with lower preexisting trust in the vaccine. Our results highlight an unintended consequence of vaccine incentives.