Lotteries
I still think the a good way to get more people vaccinated is to hand out free lottery tickets (like Megamillions tickets) at vaccine clinics. 💰
It’s unlikely people would buy less lottery tickets if they gave them away at vaccine clinics, so it wouldn’t cost the lottery bureaus anything besides the paper that they are printed on. I guess in theory you could have more winners with more tickets out there but then the prize pool would just be split in more ways.
While I don’t like gambling, I think “free” lotteries are a good way to incentivize good behavior. BF Skinner used to write about how powerful lotteries are as an incentive for behavior. Often a lottery can be more effective than a punishment.