An observational study of the association between COVID-19 vaccination rates and participation in a vaccine lottery

Abstract Objectives To examine the association between financial incentives from entry into a vaccine competition with the probability of vaccination for COVID-19. Design A cross-sectional study with adjustment for covariates using logistic regression Setting October and November 2021, Australia. Participants 2,375 respondents of the Taking the Pulse of the Nation Survey Primary and secondary outcome measures The proportion of respondents who had any vaccination, a first dose only, or second dose after the competition opened. Results Those who entered the competition were 2.27 (95% CI 1.73 to 2.99) times more likely to be vaccinated after the competition opened on October 1 st than those who did not enter—an increase in the probability of having any dose of 0.16 (95 % CI 0.10 to 0.21) percentage points. This increase was mostly driven by those receiving second doses. Entrants were 2.39 (95% CI 1.80 to 3.17) times more likely to receive their second dose after the competition opened. Conclusions Those who entered the Million Dollar Vax competition were more likely to receive a vaccination after the competition opened compared to those who did not enter the competition, with this effect dominated by those receiving second doses. Strengths and limitations of this study We use a nationally representative sample of individual self-reported vaccination status and timings. We distinguish between the association between competition entry and first and second doses. We adjust for a rich set of individual characteristics associated with vaccination status, and examine the factors influencing competition entry The strong association for second dose vaccinations may reflect some individuals who had already scheduled their second dose after the competition opened, potentially leading to an overestimate of the association.