Medicaid Expansion and US Mortality Rates During the COVID-19 Pandemic, 2018–2022

<b>Objectives.</b> To examine the association of state Medicaid expansion status with mortality changes during the COVID-19 pandemic in the United States. <b>Methods.</b> Deaths among individuals 20 to 64 years of age in 3142 counties were identified from 2018 to 2022 mortality surveillance data. Age-adjusted mortality rates were calculated for each county and by cause of death. Changes in mortality rates before and after the onset of the COVID-19 pandemic (2018-2019 vs 2021-2022) in Medicaid expansion states relative to nonexpansion states were calculated after adjustment for county sociodemographic factors and state COVID-19 vaccination rates. <b>Results.</b> All-cause mortality rates increased in 2020-2021 nationwide and decreased slightly in 2022. Overall, the increase was slower in Medicaid expansion states, leading to a net decrease of 31.8 (95% confidence interval [CI] = 20.9, 42.8) deaths per 100 000 person-years associated with Medicaid expansion from 2018-2019 to 2021-2022. The decrease was largest for deaths from heart disease and liver disease and was observed across subpopulations stratified by sex, age, and race. <b>Conclusions.</b> Increases in mortality rates were slower in Medicaid expansion states than in nonexpansion states during the COVID-19 public health emergency, suggesting a protective effect of Medicaid expansion on population health during the pandemic. (<i>Am J Public Health</i>. 2025;115(6):890-899. https://doi.org/10.2105/AJPH.2025.308045).