Abstract

Beliefs about immunity may have important consequences for health behaviors. For instance, people who overestimate their protection against a disease may neglect routine vaccinations, preventative measures, or diagnostic testing. Currently, few individuals are up-to-date on COVID-19 vaccines, leading to widespread gaps in protection. To address this challenge, we tested psychological interventions that targeted beliefs about immunity, providing personalized feedback about likely protection against COVID-19. In an online sample of participants (N=882, stratified by age and gender), this intervention effectively changed immunity beliefs and increased vaccination intentions. Furthermore, the personalized intervention effectively realigned perceived risk (Cohen’s d=0.35), whereas an existing, widely-used intervention produced by a national public health organization was ineffective (d=-0.03). The personalized intervention was particularly effective for older adults, who are at greater risk of experiencing severe illness if not sufficiently protected by vaccination. Two months later, belief changes endured, and self-reported vaccine uptake was 2-14x greater than the national rate in the United States during the same time period. Lastly, we scaled our intervention to an interactive public website and replicated our findings in an independent sample that was stratified to approximate the demographic makeup of the United States (N=553). Overall, our psychological intervention changed immunity beliefs and motivated vaccination, of relevance for COVID-19, influenza, and future pandemic threats.