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COVID vaccine incentive lotteries were tied to an increase in vaccinations, but results varied by state, researchers found.

Lottery programs were associated with an overall 2.1% (95% CI 0.7%-3.5%, P<0.001) increase in vaccine uptake and were positively associated with vaccine uptake in Oregon, Maryland, Ohio, Washington, California, and Colorado, but they had the opposite effect in Arkansas, Kentucky, and West Virginia.

Given this 2.1% estimated increase, lottery programs may have expanded vaccine coverage by about 1.78 million additional adults, Chandra Dhakal, MS, of the University of Georgia in Athens, and Binod Acharya, MS, of Drexel University in Philadelphia, wrote in a research letter.

Vaccine lotteries were some of the most publicized tools to increase vaccination uptake in the spring, when all adults became eligible for COVID vaccination. Ohio's in May launched a flurry of copycats.

"To our knowledge, this is the first study of its kind evaluating the association of this policy with vaccination rates in multiple states using both the individual responses of vaccination status and state-level daily vaccination data," Dhakal and Acharya wrote.

However, they noted that these results might not be generalizable to other states.

They examined data from adults ages 18 and up from the Household Pulse Survey in March to July 2021. Participants who answered the question "Have you received a COVID-19 vaccine?" were included. The authors also looked at daily vaccination rates for 11 states with a lottery program and 28 states without one.

Overall, data from 403,714 individuals were included. Respondents were a mean age of about 53, about 52% were women, and over three-quarters were white. About 72% were vaccinated.

Mean age was significantly higher in the unvaccinated group, with a significantly lower percentage of women and a significantly higher percentage of Black and Hispanic individuals, as well as SNAP participants and unemployment insurance recipients versus the vaccinated group. The unvaccinated group also had lower household income and education status, on average.

A difference-in-difference analysis found "a positive and significant association between the lottery program and vaccinations" in the following states:

• Oregon (6.6%, 95% CI 5.6%-7.6%)
• Maryland (6.4%, 95% CI 5.4%-7.4%)
• Ohio (5.4%, 95% CI 4.4%-6.4%)
• Washington (3.8%, 95% CI 2.8%-4.8%)
• California (2.5%, 95% CI 1.5%-3.5%)
• Colorado (2.2%, 95% CI 1.2%-3.2%)

However, there were no associations between the lottery program and vaccinations in New Mexico or New York, they noted, and the opposite association between the program and vaccine uptake in Arkansas, Kentucky, and West Virginia.

Dhakal and Acharya noted that their analysis was subject to limitations related to data collection, reporting issues, and potential self-reporting bias. However, they stressed that the heterogeneity of their results indicate that this program did not work for all states.

"We recognize that vaccine acceptance may be a much more complex process with political, psychological, cultural, geographical, or socioeconomic elements involved that could explain the differential results of lottery programs in different states," they wrote.

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