Assessing the Effectiveness of COVID-19 Vaccine Lotteries: A Cross-state Synthetic Control Methods Approach

Co-authors: Carlos Algara, Sam Fuller, & Sara Kazemian

Status: Published in 2022 in PLoS One

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Abstract: Vaccines are the most effective means at combating sickness and death caused by COVID-19. Yet, there are significant populations within the United States who are vaccine-hesitant, some due to ideological or pseudo-scientific motivations, others due to significant perceived or real costs from vaccination. Given this vaccine hesitancy, twenty state governors from May 12th to July 21st implemented some form of vaccine lottery with the aim of increasing low vaccination rates. A critical question, however, is whether these lotteries had a direct effect on vaccination. Previous literature on financial incentives for public health behaviors is consistent: Financial incentives significantly increase incentivized behaviors. Yet, work done specifically on state vaccine lotteries is both limited in scope and mixed in its conclusions. We use synthetic control methods to analyze all 20 states and causally identify for eighteen states the effects of their lotteries on both first-dose and complete vaccination rates. Within those eighteen states, we find strong evidence that all but three states’ lotteries had positive effects on first-dose vaccination. We find for complete vaccinations, however, over half the states analyzed had negative or null effects. We explore possibilities related to these mixed results including the states’ overall partisanship, vaccine hesitancy, and the size of their lotteries finding null effects for each of these explanations. We conclude the design of these programs is likely to blame: Every lottery only incentivized first-doses with no additional or contingent incentive based on a second dose. Our findings suggest the design of financial incentives is critical to their success, or failure, but generally can induce an uptake in vaccination across diverse demographic, ideological, and geographical contexts in the United States.