Promoting Vaccination with Lottery Incentives
Background: In May, 2021, U.S. states began implementing “vaccination lotteries” to encourage vaccine-hesitant individuals to get a COVID-19 vaccine. Purpose: Drawing on theories from math cognition and behavioral economics, we tested several monetary lottery structures and their framing to determine which would best motivate unvaccinated individuals. Methods: In two online experiments conducted in May, 2021, U.S. adults were asked to imagine that their state had implemented a vaccination lottery. In Experiment 1, participants (n=589) were randomly assigned to 1 of 12 conditions that varied the monetary amount and number of winners, holding constant the total payout ($5 million). In Experiment 2, participants (n=274) were randomly assigned to 1 of 4 conditions in a 2 (Message Framing: Gain versus Loss) by 2 (Numeric Framing: 5 total winners versus 1 winner for 5 weeks) factorial design; in all four conditions, 5 people would each win $1 million. Following the manipulation, participants rated their COVID-19 vaccination intentions, perceived likelihood of winning, and anticipated regret. Results: Vaccination intentions did not differ across conditions in either experiment, and post-manipulation vaccination intentions were strongly associated with baseline vaccination willingness. When asked to choose from 12 different lottery structures, participants tended to prefer options that awarded less money to more people, with 41.9% of participants across experiments indicated they would not vaccinate for any lottery-based monetary incentive. Conclusion: Findings suggest that multiple lottery structures could be equally motivating for unvaccinated adults, although states could consider structures that distribute incentives across more people.