ABSTRACT
Financial incentives are a controversial strategy for increasing vaccination. In this systematic review, we evaluated: 1) the effects of incentives on COVID-19 vaccinations; 2) whether effects differed based on study outcome, study design, incentive type and timing, or sample sociodemographic characteristics; and 3) the cost of incentives per additional vaccine administered. We searched PubMed, EMBASE, Scopus, and Econlit up to March 2022 for terms related to COVID, vaccines, and financial incentives, and identified 38 peer-reviewed, quantitative studies. Independent raters extracted study data and evaluated study quality. Studies examined the impact of financial incentives on COVID-19 vaccine uptake (k = 18), related psychological outcomes (e.g., vaccine intentions, k = 19), or both types of outcomes. For studies of vaccine uptake, none found that financial incentives had a negative effect on uptake, and most rigorous studies found that incentives had a positive effect on uptake. By contrast, studies of vaccine intentions were inconclusive. While three studies concluded that incentives may negatively impact vaccine intentions for some individuals, they had methodological limitations. Study outcomes (uptake versus intentions) and study design (experimental versus observational frameworks) appeared to influence results more than incentive type or timing. Additionally, income and political affiliation may moderate responses to incentives. Most studies evaluating cost per additional vaccine administered found that they ranged from $49-75. Overall, fears about financial incentives decreasing COVID-19 vaccine uptake are not supported by the evidence. Financial incentives likely increase COVID-19 vaccine uptake. While these increases appear to be small, they may be meaningful across populations. Registration: PROSPERO, CRD42022316086 (https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42022316086).