Different Interventions for COVID-19 Primary and Booster Vaccination? Effects of Psychological Factors and Health Policies on Vaccine Uptake.

Background: Mitigation of the COVID-19 pandemic requires continued uptake of SARS-CoV-2 vaccines. To increase vaccination intention and uptake, key determinants of primary and booster vaccination need to be understood and potential effects of vaccination policies examined.

Design: Using experimental data collected in Germany in February 2022 ( = 2701), this study investigated 1) predictors of primary and booster vaccination and 2) potential effects of policies combining vaccination mandates and monetary incentives.

Results: Compared with unvaccinated participants, those with primary vaccination were less complacent, more often understood the collective protection afforded by vaccination, and less often endorsed conspiracy-based misinformation. Compared with participants with primary vaccination, boosted individuals were even less complacent, exhibited fewer conspiracy-based beliefs, perceived fewer constraints by prioritizing vaccination over other things, and more often favored compliance with official vaccination recommendations. Support for and reactance about vaccination mandates depended on vaccination status rather than policy characteristics, regardless of mandate type or incentives (up to 500 EUR). While unvaccinated individuals rejected policy provisions and declined vaccination, boosted individuals indicated mid-level support for mandates and showed high vaccination intention. Among vaccinated individuals, higher incentives of up to 2000 EUR had a considerable positive effect on the willingness to get boosted, especially in the absence of a mandate.

Conclusions: While mandates may be needed to increase primary vaccination, our results indicate that financial incentives could be an alternative to promote booster uptake. However, combining both measures for the same target group seems inadvisable in most cases.

Highlights: Unvaccinated individuals and people with primary and booster vaccinations differ on psychological dimensions, calling for tailored immunization campaigns.Vaccination intentions depend on vaccination status rather than on mandatory or incentivizing policies.Incentives are unlikely to persuade unvaccinated individuals but may increase booster uptake.Positive effects of incentives decrease when vaccination is mandatory, advising against combination.