I wonder if people downvoted this because they took it as some kind of political point about COVID-19. Maybe it was, but I agree with it as a serious proposal. Even if the government is not confident in its ability to get people to accept vaccinations, it should commit to pay for the doses either way, to incentivize the development of the vaccine. In general, a contest or prize is a smart way to fund a public good. Among left and right economists, this is one thing most would agree on.