A decrease in coronavirus disease 2019 (COVID-19) vaccination rates has led some states to consider various incentives to boost demand for vaccines. On May 13, 2021, Ohio announced a free weekly lottery for individuals who received at least 1 COVID-19 vaccination. This study seeks to rigorously quantify the impact of Ohio's vaccination lottery.

A synthetic control consisting of a weighted combination of other states was used to approximate the demographic characteristics, new cases, and vaccination rates in Ohio prior to the lottery announcement. The difference in vaccination rates in Ohio and the synthetic control following the lottery announcement was then used to estimate the lottery's impact.

Prior to the lottery announcement, Ohio and synthetic Ohio had similar demographic characteristics and new case rates. Ohio and synthetic Ohio also had identical first vaccination rates. By the final lottery enrollment date of June 20, the percentage of the population with first vaccinations increased to 47.41% in Ohio and 46.43% in synthetic Ohio for a difference of 0.98% (95% confidence interval [CI] 0.42-1.54).

An additional 114,553 Ohioans received vaccinations as a result of the Vax-a-Million program (95% CI 49,094-180,012) at a cost of approximately $49 per Ohioan vaccinated (95% CI $31-$114). However, a majority of Ohioans remained unvaccinated by the end of the lottery, indicating that additional efforts are needed to address barriers to vaccination. This synthetic control approach may also be useful to evaluate other COVID-19 incentive programs.