Effectiveness of state-level vaccination mandates: evidence from the varicella vaccine.

This paper utilizes longitudinal data on varicella (chickenpox) immunizations in order to estimate the causal effects of state-level school-entry and daycare-entry immunization mandates within the United States. We find significant causal effects of mandates upon vaccination rates among preschool children aged 19-35 months; these effects appear in the year of mandate adoption, peak two years after adoption, and show a minimal difference from the aggregate trend about six years after adoption. For a mandate enacted in 2000, the model and estimates imply that roughly 20% of the short-run increase in state-level immunization rates was caused by the mandate introduction. We find no evidence of differential effects for different socioeconomic groups. Combined with previous cost-benefit analyses of the varicella vaccine, the estimates suggest that state-level mandates have been effective from an economic standpoint.