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Policies enacted during the COVID-19 public health emergency (PHE) extended Medicaid beneficiaries’ enrollment for several years. Following the pandemic, states used an “unwinding” process and resumed normal eligibility determinations. Subsequently, Medicaid enrollment declined nationwide by about 10 million individuals within 12 months. Despite vaccine access protections enacted through the Inflation Reduction Act in 2023, individuals who lost Medicaid coverage during unwinding also encountered barriers to accessing vaccines. States differed in how and when they chose to unwind continuous coverage and conduct redeterminations, resulting in varying impacts to healthcare coverage and vaccination rates.

Figure 1. Total Medicaid Enrollment, April to December, 2023

While the impact of unwinding on enrollment is clear, its impact on access to healthcare services—specifically, to vaccination—is less certain. While there is some public reporting of vaccination rates among Medicaid-enrolled populations, state-by-state variation in Medicaid program management, data reporting, and presentation may limit our understanding of long-term trends, both nationwide and at the state and local levels.

Further compounding these challenges are provisions in the recently passed One Big Beautiful Bill Act (OBBBA) of 2025 that require Medicaid programs to conduct eligibility redeterminations every six months (vs. every year), implement work requirements for certain adults, and change federal financing guidelines. These provisions could intensify vaccine access challenges potentially associated with unwinding and declining Medicaid enrollment immediately following the COVID-19 PHE.

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Funding for this research was provided by Pfizer. Avalere Health retained full editorial control.