The Department of Health and Human Services, specifically the Centers for Disease Control and Prevention (CDC), intends to negotiate a non-competitive modification to an existing contract with Quest Diagnostics, Inc. This modification aims to expand the scope of the contract to include access to de-identified antibody results from previously tested specimens, focusing on individuals with immunocompromising conditions as part of the CDC's Multistate Assessment of SARS-CoV-2 Seroprevalence in Commercial Laboratory Survey (MASS-C) Study. The contract modification is crucial for estimating the prevalence of SARS-CoV-2 infections and vaccinations across various demographics and geographic locations, utilizing existing data rather than incurring additional costs for new specimen collection. Interested parties may submit responses to this notice within 15 days to the primary contact, Liz Cole-Greenblatt, at qst7@cdc.gov, although the government retains discretion over whether to pursue competitive procurement.