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 must be examined.Design: Using experimental data collected in Germany in February 2022 (N = 2,701), this study investigated (a) predictors of primary and booster vaccination, and (b) potential effects of policies combining vaccination mandates and monetary incentives.Results: Compared to 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 to 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 euro). 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 2,000 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.