Discussion
SECONDARY, DISEASES
We conducted a two-stage randomized cluster trial in rural Ghana that assesses the impact of randomly assigned financial incentives on vaccination outcomes. Results from our trial in rural Ghana indicate that financial incentives increased COVID-19 vaccine uptake. The low rate of vaccinations in Africa during the recent COVID-19 pandemic was a serious global public health failure, and our results suggest that financial incentives would have improved vaccination uptake and narrowed the vaccination gap between Africa and the rest of the world.Non-vaccinated individuals assigned to the financial incentive treatment arms were 9% more likely to express an intention to get the COVID-19 vaccination. This financial incentive-intention result is consistent with other studies that reported financial incentive effects on intention to get vaccinated that varied between 4.2% and 16% (refs. A standard informative health message about the COVID-19 vaccine, or at least the message implemented in this trial, had no effect on vaccination intentions. Others have reported similar null effects, and a recent meta study suggests that online health messaging has not affected willingness to get the COVID-19 vaccineIndividuals in the financial incentive treatment arms of our trial were offered cash if they were vaccinated within a 6-week period. Two months after the initial intervention, the average self-reported COVID-19 vaccination rates for respondents in the cash treatment were about 4% higher than those for respondents in the placebo treatment (40% versus 36%). The treatment effect on reported vaccination status is roughly one-half of its effect on vaccination intention. This ratio is consistent with, for example, Dai et al.Scaling up such a financial incentive policy requires setting an optimal incentive payment for those getting a COVID-19 vaccine. To give a better sense of the magnitude of the financial incentives used in our study, the high incentive of $10 is equivalent to about 80 Ghana cedis, which is half the reported amount spent on food per week, and 41% of total weekly spending for the average household in our sample. The low incentive of $3 (equivalent to 24 cedis) amounts to about 15% and 12% of the weekly food and total spending, respectively, for the average family in our study.Our secondary pre-registered hypothesis was that the $10 treatment effect on vaccination uptake would be significantly higher than the $3 incentive. In fact, we found the opposite. Vaccination rates may not respond to higher cash incentives because the $10 payment signals low quality or potential health risksClearly context matters. Our results, along with a number of other COVID-19 vaccine experimental trials with financial incentives, suggest considerable variation in the magnitudes of incentives associated with increased vaccine uptakeAnother concern regarding financial incentive campaigns at scale is the impact that these cash payments may have on individuals who might not be eligible for the incentives or on future vaccination uptake by those who received a financial incentive. Our pre-registered expectation was that proximity to participants who received one of the two cash incentive treatments would depress the vaccine intentions and reported vaccine rates of non-treated individuals. The rural villages in the selected rural districts were quite small; on average, they had a population of 1,268. In each cash-treated village, we sampled 21 individuals, and 75% of them received the cash incentive. This would seem to be a context that would favor spillover effects from the cash treatments. To identify spillover effects from financial incentive campaigns, 25% of the individuals in cash-treated and health-message-treated villages received the placebo treatment. We found no evidence of a negative within-cluster spillover effect. Secondly, we measured the self-reported, and verified, vaccination rates of randomly selected non-treated individuals in cash-treated villages and found no evidence of spillover effects. There is no evidence supporting our pre-registered hypothesis that the cash incentives treatments would depress the vaccination intentions and behaviors of those residing in cash-treated villages who did not receive cash for vaccination. This is consistent with a recent Swedish RCT that found no evidence of a spillover effect of COVID-19 financial incentives on future vaccination uptakeAlthough we are confident in our spillover conclusion in the context of our study, we cannot rule out the possibility that, in a larger-scale roll-out of financial incentives, where a substantial proportion, but not all, of a population was offered incentives, there might be negative spillovers on untreated individuals arising from greater diffusion of information.We explicitly timed the implementation of our incentive trials to correspond with the COVID-19 vaccination campaigns conducted by District Health Offices. COVID-19 vaccinations were available to all villages, and, in most cases, the District Health Offices made the vaccines available in the village communities. This is important because, as a recent trial in rural Sierra Leone demonstrated, by solving the delivery challenges and markedly increasing convenience, COVID-19 vaccine uptake increased by 19% (ref. Our study has some limitations. First, in each of our sampled villages, we were not able to precisely document the availability of COVID-19 vaccine supplies and the phase of the vaccine roll-out that was occurring when our intervention was implemented. Second, the results could be conditional on the particular design, content and delivery of the video messages. Third, we cannot rule out the possibility that a much larger-scale roll-out of financial incentives might be accompanied by greater diffusion of information and negative spillovers to untreated individuals, although there is no indication from our results that these spillovers are more likely to be negative than positive. Fourth, the context was financial incentives for adults for vaccination against COVID-19 in rural Ghana; treatment effects and spillover effects may be different among different populations (urban settings, for example) and for vaccination against different diseases. Nevertheless, our study is one of the few COVID-19 financial incentive studies that measures actual vaccination outcomes. The results provide insights for the rural Ghana population and may have relevance for the approximately 50% of the overall African population living in non-urban settings