CDC is working with state, local, territorial, academic, and commercial partners to better understand COVID-19 in the United States. CDC has an overarching strategy for learning more about how many people have been infected with SARS-CoV-2, the virus that causes COVID-19, and how it is spreading through the U.S. population. This strategy includes using serology testing for surveillance to better understand how many infections with SARS-CoV-2 have occurred: • At different points in time, • In different locations, and • Within different populations in the United States. Serology tests look for antibodies in blood. If antibodies are found, that means there has been a previous infection. Antibodies are proteins that can fight off infections. Investigations using serology testing are called seroprevalence surveys. CDC is collaborating with public health and private partners on a variety of seroprevalence surveys of different sizes, locations, populations studied, and purposes. The seroprevalence surveys CDC is conducting include large-scale geographic surveys, community level surveys, and smaller-scale surveys focusing on specific populations in order to learn more about COVID-19.

Stephen B. Thacker CDC Library collection