Risk Compensation: How Vaccination Impacts Social Distancing in an Online Natural Experiment.

Amidst mass immunization efforts to curb COVID-19 transmission, policy mandates enforced minimum physical distancing. Concerns arose regarding risk compensation, where individuals might reduce adherence to distancing if benefiting from multiple risk-reducing interventions. This study used an online natural experiment to examine the association of vaccination status and vaccine efficacy beliefs with social distancing preferences. Participants completed a distance-matching task, positioning avatars in stylized scenarios drawn from a 2 (location) × $\times$ 3 (activity) factorial design. Data were collected in July 2021 during the vaccine rollout program in the United Kingdom. Contrary to risk compensation expectations, this study found no strong evidence of reduced distancing at a population level. However, stronger vaccine efficacy beliefs were associated with slightly reduced distancing among fully vaccinated individuals-a small effect size. In contrast, partially vaccinated and unvaccinated individuals with stronger vaccine beliefs maintained greater distance, suggesting a nuanced relationship between perceptions of vaccine efficacy and distancing behavior. Subjective risk perceptions did not significantly alter these patterns. Additionally, partially vaccinated individuals behaved similarly to the unvaccinated despite expressing higher perceived infection risk, and unvaccinated participants who intended to vaccinate showed lower distancing preferences. The study also identified an in-group bias in perceptions of vaccine distribution. While these findings were collected during a specific phase of the COVID-19 pandemic-when vaccination uptake and policy measures were rapidly changing-they underscore the importance of investigating how vaccine beliefs shape protective behaviors. Given the modest effect sizes observed, further research is warranted to clarify the evolving role of vaccine perceptions in public health strategies.