While incentives are often easier to implement, as they do not normally induce such opposition, it is likely that a combination of incentives and penalties will be needed to raise vaccination rates to a high enough level to effectively combat COVID.
Incentives haven’t been put to the test
Unlike the development of COVID vaccines, which were only made available to the public after a careful evaluation of RCT evidence, policies to promote vaccine uptake through incentives or penalties appear to be introduced without any formal testing to evaluate their effectiveness.
Take the Ohio vaccine lottery, introduced in May, which involved giving cash prizes of up to a million dollars for those getting vaccinated. There have now been at least four studiestrying to retrospectively estimate its effect on vaccine uptake, two of which have found that the lottery had no effect and two which have found it promoted uptake. While it’s tempting to repeat Winston Churchill’s quip that “if you put two economists in a room, you get two opinions”, it illustrates the difficulties of conducting policy evaluation without the benefit of being able to randomise.
Are randomised vaccine incentives experiments really possible? One way is to take advantage of the multitude of incentives across the US, making it the world’s vaccine-incentive policy laboratory. All one needs to do is add randomisation to see what works.
We recently took this approach by randomly allocating just over 1,600 unvaccinated Americans to one of three brief video messages, including information that those getting vaccinated might be eligible for a cash payment or a vaccine lottery. Our results, which we uploaded to the medRxiv preprint server, show that cash incentives, but not vaccine lotteries, are likely to promote vaccine uptake. An extra 5% of those seeing the video about cash incentives clicked through to get information on where they could get vaccinated.
Beyond understanding the overall effects of incentives and penalties, it is important to look at what works best in key sub-populations. This particularly includes those populations with low vaccine uptake and those most likely to spread COVID in the community.
When it comes to incentives to promote vaccine uptake, evidence from RCTs is the sieve that separates good policies from bad ones.