Abstract
This cohort study examines changes in COVID-19 vaccination rates across US states with lottery-based vaccine incentives.
On May 12, 2021, Ohio announced a lottery system incentivizing residents to receive COVID-19 vaccinations1; several US states subsequently introduced similar programs.2 Although analysis of vaccination rates from Ohio suggested that lottery-based incentives were not associated with increased vaccination rates,3 responses to lottery programs across other states are unclear. In this study, we assessed changes in COVID-19 vaccination rates across US states with lottery-based vaccine incentives.
Methods
We identified lottery states that announced cash prizes for vaccinated individuals from May 24, 2021, to July 19, 2021. States that announced lotteries outside of this period were excluded; other states were non–lottery states. This study was deemed not human participants research by the Boston University Medical Campus institutional review board. Dates were chosen to minimize confounding from vaccine expansion to adolescents (May 10, 2021). Daily rates of first COVID-19 vaccine dose administration per 100 000 persons from May 17, 2021, to July 26, 2021, were obtained from the US Centers for Disease Control and Prevention.4 Using interrupted time series analyses with segmented regression,5 we estimated the (1) immediate level change and (2) trend change in (1) daily vaccination rates in lottery states and (2) differences in daily vaccination rates between lottery and non–lottery states after vaccine lottery announcement (primary analysis), with date and state as random intercepts (eMethods in the Supplement). Sensitivity analyses included (1) using state-reported vaccination data when available and (2) a model with state as a fixed effect. A post hoc sensitivity analysis explored states with more than 3 weeks of prelottery data. We also estimated the cumulative difference in vaccines administered during the postlottery period in lottery states compared with what would have been expected from prelottery trends (eMethods and eTables 1 and 2 in the Supplement). Statistical testing was 2-tailed with an α level of .05 using R, version 4.0.2 (R Project for Statistical Computing).
Results
Daily first vaccination rate trends of 15 lottery and 31 non–lottery states are shown in the Figure. Among lottery states, the vaccination rate decreased before lottery announcements (–2.8 [95% CI, –4.2 to –1.4] vaccinations/100 000 people/day); following lottery announcements, vaccine administrations did not significantly increase (–0.4 [95% CI, –23.5 to 22.7] vaccinations/100 000 people), and vaccination trends did not significantly change (0.7 [95% CI, –0.9 to 2.4] vaccinations/100 000/day) compared with prelottery trends.
Figure. Trends in Vaccination Rates Before and After Vaccine Lottery Announcements Among US States.
The segmented regression lines show vaccination trends in the weeks before and after each state's vaccine lottery announcement (marked with the vertical black dotted line). The shaded areas represent 95% CIs. The blue line denotes vaccine rates in lottery states, whereas the orange line denotes vaccine rates in non–lottery states.
Vaccination rate trends were similar between lottery and non–lottery states before lottery announcements (–0.5 [95% CI, –1.7 to 0.82] vaccinations/100 000 people/day; P = .69). After lottery announcements, there was no significant difference in vaccination level change (1.1 [95% CI, –21.7 to 23.8] vaccinations/100 000 people; P = .92) and no change in trend in vaccination rate difference (0.4 [95% CI, –1.1 to 2] vaccinations/100 000 people/day; P = .59) between lottery and non–lottery states. Sensitivity analyses with (1) state-reported data from 4 lottery states and (2) states as fixed effects showed similar results (Table). A sensitivity analysis of states with more than 3 weeks of prelottery data found no significant difference in vaccination levels and a borderline significant increase in trend after lottery announcements (P = .05). In the primary analysis (all states), the estimated cumulative difference in vaccines administered during the 28-day postlottery period in lottery states compared with what would have been expected without lottery adoption was 190 vaccines per 100 000 people (–1063 to 1484 vaccines/100 000 persons); in a post hoc sensitivity analysis (states with >3 weeks of prelottery data), the estimated change in vaccinations was 1092 per 100 000 people (–616 to 2800 vaccines/100 000 persons).
Table. Difference in Vaccination Rates Between Lottery and Non–Lottery US States.
| State | Vaccination rate trend during the 4 wk before lottery announcement, vaccines/100 000 persons/d (95% CI) | Vaccination rate immediately after lottery announcement, vaccines/100 000 persons (95% CI) | Vaccination rate trend change during the 4 wk after lottery announcement, vaccines/100 000 persons/d (95% CI) | Estimated cumulative difference in vaccines administered during the postlottery period/100 000 persons (extrapolated range) | ||
|---|---|---|---|---|---|---|
| Combined lottery states | ||||||
| CDC data | –0.5 (–1.7 to 0.8) | 1.1 (–21.7 to 23.8) | 0.4 (–1.1 to 2.0) | 190 (–1062 to 1484) | ||
| Using state data | 0.5 (–0.7 to 1.7) | –0.4 (–21.9 to 21) | –0.6 (–1.9 to 0.8) | –255 (–1387 to 913) | ||
| State as fixed effect | –0.6 (–1.8 to 0.7) | 1 (–21.5 to 23.5) | 0.5 (–1.1 to 2.0) | 231 (–1063 to 1484) | ||
| Seven lottery states with >3 wk of prelottery data | –1.6 (–2.9 to –0.2) | 10.0 (–21.7 to 41.9) | 2.0 (0 to 4.0) | 1092 (–616 to 2800) | ||
Abbreviation: CDC, US Centers for Disease Control and Prevention.
Conclusions
This study did not find evidence that vaccine lottery incentive programs in the US were associated with significantly increased rates of COVID-19 vaccinations. These findings expand on similar findings from the first state vaccination lottery.3 The models may be underpowered to rule out small to moderate increases in vaccination rates.6 The findings depend on the accuracy of US Centers for Disease Control and Prevention vaccine data; however, sensitivity analyses using data reported by a subsample of states that reported daily vaccination rates resulted in similar findings. Given the lack of a strong association between state lottery-based vaccine incentives and increased vaccination rates, further studies of strategies to increase vaccination rates are needed.
eMethods. Description of statistical analysis
eTable 1. Vaccine lotteries by state
eTable 2. Analysis dataset
References
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
eMethods. Description of statistical analysis
eTable 1. Vaccine lotteries by state
eTable 2. Analysis dataset