Pol Campos-Mercade

Title: Incentives, Surrogates, and Long-run Vaccination

Abstract: Can monetary incentives improve health behaviors in the long run, and do commonly used surrogate outcomes capture these effects? We study these questions in the context of vaccination using a large-scale field experiment. The experiment combines commonly used surrogates—vaccination intentions, intermediate behavioral proxies, and short-run vaccination—with long-run administrative vaccination records. We first document that incentives increase vaccination rates in the long run: guaranteed $20 incentives raise COVID-19 booster uptake by 9 percentage points. Lottery-based incentives also increase long-run uptake, while prosocial incentives primarily accelerate vaccination. Second, using surrogacy methods, we study whether surrogates can predict long-run impacts. Although the surrogates are strongly correlated with eventual vaccination, the assumptions required for surrogacy methods are often violated, and they do not accurately predict long-run impacts. Our findings highlight both the ability of incentives to change behavior and the importance of measuring long-run outcomes rather than relying solely on surrogates.