This project will provide laboratory support for a large, cross-sectional COVID-19 seroprevalence study that will be conducted in 15 communities in the United States: the SARS-CoV-2 Seroprevalence Study (COVID-19 Prevention Trials Network [CoVPN] 5002). The CoVPN 5002 study will include collection of data and specimens from up to 58,800 persons, including persons living in nursing homes and assisted living facilities, persons attending clinics, and persons living in study communities. The study will include children (ages 2 months and older) and adults. Participants will be tested for COVID-19 in real time using SARS-CoV-2 RNA assays. Seroprevalence will be assessed retrospectively using stored specimens from all participants using a sensitive and specific SARS-CoV-2 IgG assay (Abbott ARCHITECT COVID-19 IgG test, which detects the presence of IgG antibodies against the SARS-CoV-2 nucleocapsid protein). A subset of specimens from CoVPN 5002 will also be used to evaluate the performance of diagnostic and serologic SARS-CoV-2 assays using alternate specimen types (saliva and dried blood spots). Collection of these sample types is simpler and less invasive than collection of nasal swabs or collection of blood samples by phlebotomy. This project will also use of specialized assays to evaluate the serologic response to SARS-CoV-2. This may include use of a massively multiplexed antibody profiling assay to measure antibody binding to SARS-CoV-2 peptides spanning the viral genome. This analysis may provide information on the fine specificity of the antibody response to SARS-CoV-2 and reactivity to other coronaviruses and other viruses that cause respiratory illnesses. This testing may also identify participants who have false positive or false negative test results using the ARCHITECT COVID-19 IgG test. Findings from this research will inform the design of clinical trials for SARS-CoV-2 prevention and treatment by providing information about the seroprevalence of COVID-19 in diverse geographic regions and participants groups, including asymptomatic and symptomatic individuals, children and adults in the general population, and adults at increased risk for COVID-19.