Covid-19 vaccine incentives' effectiveness and differential impact on high-risk groups: A prospective cohort study

We sought to evaluate the impact of guaranteed immediate cash incentives on Covid-19 vaccine initiation. We hypothesized that incentives' impact is bigger at vaccination sites serving higher risk patients.

Participants were 4,303,542 adults who received a first Covid-19 vaccine dose in North Carolina, US from December 2020 through August 2021. The state's incentive program guaranteed payments of $25 (and later $100) immediately after receiving the first dose of Covid-19 vaccine or $25 for providing transportation. Analyses used a difference in differences approach.

Covid-19 vaccine initiation declined less over time in the 32 vaccination sites offering incentives than in 2352 comparison sites (interaction p < .001). Incentive program vaccination sites saw Covid-19 vaccine initiation fall from an average of 382 doses per week to 72 doses. This was a decline of 81% in unadjusted analysis, and 51% after adjusting for covariates (IRR = 0.49, 95%CI = 0.46-0.52). Sites not offering the incentives saw Covid-19 vaccine initiation fall from an average of 168 doses per week to 24 doses. This was a decline of 86% in unadjusted analyses, and 83% in adjusted analyses (IRR = 0.17, 95%CI = 0.17-0.18). The incentive program was more effective for sites serving more patients who were young, male, Hispanic, and American Indian and Alaska Native (3-way interactions, all p < .001) but not Black.

Vaccination sites offering incentives had a smaller decline in Covid-19 vaccine uptake, though the mechanism requires additional study. Vaccine incentive programs may be more effective at sites serving more younger, male, Hispanic and Native patients.