Did the Medicaid expansion improve immunization among U.S. pregnant women?

We contributed different national data on understudied populations and the triple-difference method to the literature. Income-based Medicaid expansion did not increase the likelihood of vaccination among pregnant women. Non-income-based policies may target Medicaid-enrolled pregnant women in expansion states for influenza vaccination. Future interventions may target high-parity, low-education, and African American pregnant women in high-poverty non-expansion states.