In the decades preceding the COVID-19 pandemic, emergency department (ED) use increased more rapidly for socioeconomically disadvantaged patients than for advantaged patients, often because of barriers to accessing office-based care. However, it remains unknown whether the pandemic has had durable effects on socioeconomic disparities in ED use. We conducted a retrospective cohort study of ED visits in the US, using multipayer claims data. We used a difference-in-differences approach to compare ED visit rates between March 2020 and August 2022 with rates from the same months of 2018-19. Among 15.6 million ED visits, potentially avoidable visits persistently declined for all insured populations during the pandemic period. Potentially nonavoidable visits also declined early in the pandemic but rebounded to more than 95 percent of expected rates. However, stratifying by insurance revealed that this rebound occurred among commercially insured and Medicare fee-for-service patients
potentially nonavoidable visits only returned to about 75 percent of expected rates among Medicaid and dual-eligible patients. Although this suggests a beneficial reduction in potentially avoidable ED use, it also indicates the simultaneous emergence of a disparity wherein socioeconomically disadvantaged groups may be underusing the ED for potentially higher-acuity illness.