Objective: To assess the impact of increasing incentive size and reminder calls on the measles vaccine uptake rate.
Design: Randomized controlled trial, randomized at individual level, stratified by clinic.
Setting: Nigeria.
Participants: 1088 caregivers with children aged nine months or older; had received at least one previous conditional cash transfer (CCT) at a program clinic, had received their Penta-3 immunization but had not yet received their measles immunization, and the caregiver had provided a phone number.
Intervention: Nine clinics were randomized to two models; caregivers in Model 1 received a default of 2000 Nigerian Naira (NGN) for completing the measles vaccine, and those in Model 2 received by 3000 NGN. Caregivers from the respective clinics were then randomized to one of the four arms: 1) control (baseline amount of 2000 NGN or 3000 NGN), 2) baseline amount plus a reminder call, 3) baseline amount plus 1000 NGN and a reminder call, and 4) baseline amount plus 3000 NGN and a reminder call.
Main outcome measure: Receipt of measles vaccine as reported on a child health card.
Results: Overall, there was no clear trend that increasing the incentive amount resulted in an increase in vaccine uptake rates. In Model 1 households, an additional 1000 NGN and 3000 NGN resulted in a 6.4 percentage point (95% CI: -2.3-15, p-value = 0.15) and 11.8 percentage point (95% CI: 3.9-19.6, p-value = 0.003) increase in the probability of completing the measles vaccines, respectively. This increase, however, was only significant for the 3000 NGN increase. On the other hand, in Model 2 households, increasing the incentive by 1000 NGN and 3000 NGN increased the probability by 3.3 (95% CI: -3.8-10.4, p-value = 0.36) and 3.3 (95% CI: -3.7-10.4, p-value = 0.35) percentage points. These increases were not statistically significant. Adding reminder calls to CCTs increased the probability of completing the measles vaccine; caregivers who received reminder calls plus CCTs were 5.1 percentage points more likely to get their children vaccinated (95% CI: 0.50-9.8, p-value = 0.03) compared to those who received CCTs and did not receive a reminder call. These results were largely driven by caregivers who went to clinics in Model 1.
Conclusion: A combination of increasing incentive amounts and reminder calls modestly improves measles immunization rates. However, this program also shows that there is substantial regional heterogeneity in response to both incentives and calls. While one possible conclusion is that a larger incentive and phone reminders are more likely to work in higher income and higher baseline coverage settings, the study is not designed to evaluate this claim. Rather, policymakers could consider experimenting with a similar low-cost calling study as part of the design of other cash transfer programs to identify whether adding reminder phone calls could increase the impact of the program.