A third of the U.S. population — about 110 million people — are not fully vaccinated against COVID-19. To encourage more people to get vaccinated, some states have tried offering incentives, from free beverages at restaurants to a ticket for a $5 million lottery.

Harsha Thirumurthy
Harsha Thirumurthy, PhD

Incentives can promote health behaviors, including quitting smoking or losing weight, but studies investigating whether they work to increase COVID-19 vaccination have had conflicting results. So LDI Senior Fellow Harsha Thirumurthy, PhD led a study to examine their effect more comprehensively. In an analysis of incentive programs in 24 states, Thirumurthy and his coauthors — LDI Fellows Katherine L. Milkman, PhD, Kevin G. Volpp, MD, PhD, and Alison M. Buttenheim, PhD, MBA and colleague Devin G. Pope from the University of Chicago — showed they had little, if any, effect. But intriguing differences among states suggest strategies for creating financial incentives that might promote COVID-19 vaccination.

Katherine Milkman, PhD

The study, which used state-level data on daily vaccine doses from April 1, 2021, before the first statewide incentive program began, through July 29, 2021, improved on prior studies on incentives and COVID-19 vaccination that had limitations such as data from a single state or point in time. Thirumurthy and colleagues also accounted for factors that affect response to incentives, including variations in value and type.

Analyses considered the effects of guaranteed rewards vs. lotteries, whether the program was introduced early vs. late in the analysis period, and whether programs were in states that leaned Republican vs. Democratic based on the 2020 presidential election. (In a previous study, Thirumurthy demonstrated that political views affect individual responses to COVID-19.) The researchers compared these data to the control group of 26 states with no statewide incentive program. The researchers also adjusted for national vaccination trends, which declined over the period when incentives were introduced.

Kevin Volpp
Kevin Volpp, MD, PhD

They found that the incentives did not significantly change vaccination rates compared to states that had no statewide incentives. The results were the same for the 6 states with guaranteed rewards as for the 18 states with lotteries. Nonetheless, the analysis showed a slight positive effect on vaccination rates in Republican-leaning states (increased daily vaccination of 57/100,000 individuals) and a slight negative effect in Democratic-leaning states (daily decline of 51/100,000 individuals). The authors noted that the Republican-leaning states started with much lower vaccination rates than the Democratic-leaning states.

Alison Buttenheim
Alison Buttenheim, PhD, MBA

The authors concluded that the incentives did not result in meaningful changes in vaccination rates, but might have had small effects on vaccine uptake. They noted that to be persuasive, future incentives to promote vaccination might need to be more substantial than the small rewards or low-probability lotteries that many states offered. Furthermore, they noted that underlying motivation likely plays a role in the success of incentive programs; for instance, individuals who want to lose weight or stop smoking may respond to incentive programs focused on these behaviors but may have less desire to get vaccinated. Finally, the authors noted that low awareness of incentive programs, as well as mistrust and misinformation, could impact their success. In short, to effectively increase in vaccination rates, incentives may need to be more substantial or be mandates — using sticks rather than free carrots.

The study, Association Between Statewide Financial Incentive Programs and COVID-19 Vaccination Rates, was published in PLoS ONE on March 30, 2022. Authors include Harsha Thirumurthy, Katherine L. Milkman, Kevin G. Volpp, Alison M. Buttenheim, and Devin G. Pope.

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