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

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 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. 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 ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement This research was funded by the Summer Foundation (grant number: N/A) and used data from The Taking the Pulse of the Nation (TTPN) Survey run by the Melbourne Institute: Applied Economic and Social Research, University of Melbourne. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: This study was approved by the University of Melbourne Faculty of Business and Economics & Melbourne Business School Human Ethics Advisory Group (Ref: 2056754.1). I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes Statistical code for the analysis s available from the Dryad repository. TTPN Survey is a proprietary data set and researchers interested in replication need to seek access to the TTPN survey by contacting the Melbourne Institute.