Indoor vaccine mandates in U.S. cities, vaccination behavior, and COVID-19 outcomes

Abstract

Many U.S. cities introduced indoor vaccine mandates in 2021–2022 to increase COVID-19 vaccination and curb transmission. While national mandates abroad boosted uptake, the effects of city-level mandates in the U.S. remain unclear. Using the synthetic difference-in-differences methodology, we estimate the impact of mandates in nine major cities on first-dose uptake, cases, and deaths. We find no consistent pattern of significant effects, and results are robust across estimators, outcome definitions, lag structures, and donor pool choice. The contrast with international findings suggests localized mandates may be less effective in settings with high baseline coverage, mobility across jurisdictions, and vaccine hesitancy.