An observational study of the association between COVID-19 vaccination rates and entry into the Australian ‘Million Dollar Vax’ competition

Abstract ObjectivesTo examine the association between financial incentives from entry into a vaccine competition with the probability of vaccination for COVID-19. DesignA cross-sectional study with adjustment for covariates using logistic regression SettingOctober and November 2021, Australia. Participants2,375 respondents of the Taking the Pulse of the Nation Survey Primary and secondary outcome measuresThe proportion of respondents who had any vaccination, a first dose only, or second dose after the competition opened. ResultsThose 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 1st 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. ConclusionsThose 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 studyWe 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 entryThe 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.