Abstract Purpose: The COVID-19 pandemic disproportionately impacted racial/ethnic minority and low-income individuals and resulted in significant disruptions in preventive care for all groups. While severe declines in routine cancer screening were observed during pandemic shutdown periods, it is unclear whether return-to-screening rates following healthcare reopening are consistent across all groups. In this study we examine rates of breast cancer screening pre- and post- pandemic shutdown periods across race/ethnicity, age, and income among health plan enrollees in the United States (US) to inform screening catch-up strategies after COVID-19 disruptions. Methods: We conducted a retrospective analysis of breast cancer screening claims (including codes for mammography, breast MRI, digital breast tomography, and breast imaging) from Optum Clinformatics Data Mart among female enrollees from 2019-2021. Eligible enrollees included women, ages 40-75 with continuous enrollment 12 months prior to screening index month. Screening volume was calculated each calendar month during the three-year period, with January 2019-February 2020 as the pre-pandemic period, March 2020 through June 2020 as the pandemic closure period, and July 2020-December 2021 as the post-closure (reopening) pandemic period. We conducted an event study to calculate group-level monthly predicted probabilities of screening using a linear probability model with group interactions by month, controlling for demographic variables and comorbidities. Additionally, we used difference-in-difference (DD) regressions including group interacted with a post-closure pandemic dummy. The pandemic closure period months were excluded from our DD analysis. Results: Our study included 8,378,296 health plan enrolled women. Overall mammography screening decreased significantly during the pandemic closure phase (March-June 2020) but rebounded to higher levels in the post-closure period relative to baseline (3.76% to 3.96%). Screening rates were highest among non-Hispanic White women in the pre-pandemic period compared to other racial-ethnic groups. Our DD model suggests that White-Asian disparities increased in the post-pandemic period while other race/ethnic disparities remained constant. Additionally, disparities in screening by age changed during the pandemic. Although the oldest age group (65-75) had the highest screening rates in the pre-closure phase, they were slower to return to pre-pandemic levels of screening compared to younger age groups. Implications: Return to breast cancer screening among health plan enrollees in the US was robust. However, disparities in screening rates between groups in the pre-pandemic period were again observed in the reopening period, signaling lost opportunities to revamp structural inequities in care delivery following the pandemic. Further monitoring of return-to-screening disparities, particularly among more medically underserved groups, will be critical in informing interventions to address the long-term consequences resulting from the disruption of COVID-19 on cancer care. Citation Format: Jennifer Tsui, Sarah Axeen, John Thacker, Sonali Saluja, Laura Solano, Willow Pastard, Chun Nok Lam, Todd Schneberk, Cameron Kaplan. Disparities in breast cancer screening resumption among health plan enrollees in the US following the COVID-19 pandemic: Are all groups back on track? [abstract]. In: Proceedings of the 16th AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2023 Sep 29-Oct 2;Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2023;32(12 Suppl):Abstract nr C131.