Rationale: Vaccination uptake is a major strategy to prevent infection with SARS-CoV-2 and curb the transmission of COVID-19. However, many people remain unwilling to receive the COVID-19 vaccine.

Objective: Using default nudges, the present study examines (a) whether opt-out policy and its improvements could increase intention and attitude to get vaccinated and (b) whether these default effects differ across diverse risk-perception groups.

Method: An online experiment with 1926 unvaccinated Chinese respondents was conducted in February 2021. We measured willingness to be vaccinated after informing opt-in policy, standard opt-out policy, and its five improvements (opt-out education, opt-out opportunity, opt-out social norm, opt-out feedback, and opt-out op-portunity). Risk perception of the pandemic of COVID-19 and vaccination were also measured.

Results: (a) Opt-out policy and its improvement (except the opt-out transparency) increased intentions to be vaccinated. Policies with a vaccination default did not weaken people’s attitude toward policy and policymakers compared with the opt-in policy, but participants in the transparent improvement group reported lower freedom of choice than those in the opt-out group. (b) Further latent profile analysis revealed four classes underlying risk perception: risk exaggerators, risk deniers, disease-specific risk perceivers, and vaccine-specific risk perceivers. But there was no conclusive evidence that the effect of risk perception differs as a function of defaults.

Conclusions: These findings provide new psychological evidence for formulating more targeted vaccination policies and highlight the importance of risk perception to understand vaccination intentions.