A vast literature within health and behavioral economics focuses on incentivizing healthy behaviors, with economists and other behavioral scientists studying ways to promote activities such as exercising, weight loss, smoking cessation, blood donation, and vaccination. Financial incentives are often proposed as means to encourage healthy behaviors, though fundamental questions remain about how they work in practice. There is widespread disagreement among researchers concerning the efficacy of financial incentives, whether they backfire for certain people, what types of incentives work best, and whether they have unintended consequences.
In this paper, the authors study the impacts of financial incentives using a randomized controlled trial (RCT): A study design where participants are randomly assigned to either a treatment group or a control group to objectively measure the effects of an intervention. that incentivized a sample of the Swedish population to receive their COVID-19 booster vaccine. The authors divide their sample into a control group and four treatment groups that each receive one of the following four incentives if they obtain their booster within thirty days of the experiment: a guaranteed incentive of $20, a lottery incentive with an expected value of $20, a donation to charity of $20, or a selection between any of the preceding three incentives. The authors use vaccination records covering participants, their married partners, parents, and their children to observe vaccination behavior over the 22 months following the intervention. They find the following:
- Each incentive has a large impact on vaccination uptake, with guaranteed incentives the most effective. In the control group, 32% of participants took the vaccine within 30 days of the experiment. In comparison, 45% of individuals in the guaranteed incentives group vaccinated within 30 days, compared to 41% in the lottery group and 37% in the donation group.
- Incentives not only accelerate vaccination uptake but also substantially increase long-run vaccination rates. Participants in the guaranteed incentives group were not only 13 percentage points more likely to get vaccinated within 30 days, but also showed a 9 percentage points higher uptake 22 months after the intervention. Results are similar for the lottery and choice groups.
- The authors’ various incentives raise vaccination rates irrespective of participants’ backgrounds, preferences, and vaccine attitudes. In addition, the donation incentive is more effective among the most prosocial individuals than among the most selfish individuals.
- The authors consider the efficacy of targeting certain treatments to specific subgroups, given that some groups might react more strongly to the lottery or charitable donation conditions. They conclude, however, that the guaranteed incentives are the most effective across different participant groups.
- Allowing participants to choose their own incentive scheme results in similar vaccination rates to assigning incentives at random. Participants do tend to choose a variety of incentive schemes, however, with 42% choosing guaranteed, 28% lottery, and 30% donation, largely depending on their social and risk preferences.
- There is no evidence of unintended consequences of incentives on future adherence to vaccination schedules.
- Financial incentives have sizable positive spillover effects on partners who were not incentivized. Incentives, when combined across all groups, lead to a 7-percentage-point increase in vaccination uptake among the partners of the participants, an effect about half as large as the direct effects of the incentives on the participants themselves. There is little evidence of such spillovers between parents and children.
- Simply measuring how financial incentives impact participants’ intentions to vaccinate, rather than their actual vaccination status, may not accurately capture how this and related programs affect vaccination rates.
The upshot is that incentives are highly effective at promoting COVID-19 vaccination. This research has implications for incentivizing other important vaccines where the population is also urged to take multiple doses — such as flu, measles, or human papillomavirus. These findings highlight the potential of incentives to improve public health, as a large share of the burden of disease comes from vaccination-preventable diseases.