reviewed the empirical literature on behavioral responses to incentive payments and identified a range of settings in which extrinsic rewards could backfire, often due to signaling or crowding out of intrinsic motivation. Rutschman and Wiemken (2021) reviewed potential risks specifically in the context of vaccination, noting in the case of COVID-19 vaccines that payments lacked rigorous evidence, that incentive policies could be instrumentalized to question the safety and public health value of vaccination, and that incentives could exacerbate socioeconomic and racial disparities. In a qualitative study, McNaughton et. al. (2016) showed that incentives were perceived negatively and risked backfiring in a pilot program in the United Kingdom. In a randomized controlled trial in California, Chang et al. (2021) found that financial incentives and other behavioral nudges did not increase vaccination rates, and in fact decreased vaccination rates for some subgroups. Armiento et al. (2020) studied the impact of a “No Jab, No Pay” policy which disqualified unvaccinated recipients from family assistance payments and found the policy did not increase vaccine uptake. White et. al. (2019) found loyalty-points type phone applications did not increase vaccination in Canada. Dave et. al. (2021) found that the lotteries launched for vaccinated residents in 19 US states failed to increase uptake of the COVID-19 vaccine. Kreps et al. (2021) conducted a conjoint experiment and found incentives (between $10 and $100) were not associated with higher vaccine uptake among American respondents. Although Robertson et. al. (2021) found incentives may on average increase vaccination uptake in the United States (using an experimental approach very similar to the present study), the authors also found a potential backfire effect among some sub-groups. Thus, while the existing literature often finds cash transfers effective for encouraging vaccination, results vary significantly, depending on both the context and program design. One other notable difference between many early studies of vaccine incentives and those focused on vaccinations following the COVID-19 pandemic is that earlier studies were often focused on social safety net interventions for poor households, with conditions intended to improve the utilization of health services among the poor. More recent COVID-19 focused interventions are less often limited to this segment of the population.

To study the external validity of previous findings in novel settings, we conducted three nationally representative survey-based randomized controlled experiments on hypothetical cash incentives for COVID-19 vaccination in countries that have not previously appeared in this literature – Kazakhstan, Tajikistan, and Uzbekistan. To our knowledge, this is the first such experiment to comparatively study the effectiveness of monetary incentives to encourage vaccination across multiple countries.

In two of the three countries we find large and significant effects directly opposite to those expected: survey respondents randomly assigned offers of a hypothetical monetary incentive were significantly less likely to agree to be vaccinated. Negative effects on COVID-19 vaccination intentions were large and statistically significant (in Kazakhstan and Uzbekistan). For the third country (Tajikistan), a negative direction was recorded but was not statistically distinguishable from the control group. Across all three countries, higher incentive payment values were not systematically associated with increased vaccination intentions. Follow-up survey questions confirmed that in those settings where the demotivation impacts were strongest, paying incentives for vaccines was a highly unpopular option. About three-quarters of respondents in Uzbekistan actively opposed providing cash incentives for vaccination. In Kazakhstan, 58 percent said they disagreed with paying incentives. Only in Tajikistan, where the experiment failed to find any systematic effect on vaccination intentions, did just 18 percent say they disagreed with paying incentives.

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