CDC has updated its guidance for people who are fully vaccinated. See Recommendations for Fully Vaccinated People.
CDC recommends schools continue to use the current COVID-19 prevention strategies for the 2020-2021 school year. Learn more
Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
Getting vaccinated prevents severe illness, hospitalizations, and death. Unvaccinated people should get vaccinated and continue masking until they are fully vaccinated. With the Delta variant, this is more urgent than ever. CDC has updated guidance for fully vaccinated people based on new evidence on the Delta variant.
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.

Large-scale Geographic Seroprevalence Surveys

Large-scale Geographic Seroprevalence Surveys

CDC is conducting several large-scale geographic seroprevalence studies to learn more about the percentage of people in the United States who have been infected with SARS-CoV-2, the virus that causes COVID-19. This involves working with state, local, territorial, academic, and commercial partners to better understand COVID-19 in the United States using serology testing (antibody testing) for surveillance (“seroprevalence surveys” or “serosurveys”). CDC also wants to better understand how the virus is spreading through the US population over time. Because infected people can have mild illness or no symptoms (and therefore might not get medical care or testing), CDC is collaborating with commercial laboratories and blood collection centers on a variety of large-scale geographic seroprevalence surveys across the United States.

These seroprevalence surveys use blood tests to identify people in a population who have antibodies against SARS-CoV-2. Antibody test results can provide information about previous infections in people who had many, few, or no symptoms. It is not yet known if having SARS-CoV-2 antibodies can protect against getting infected again. Evidence suggests that detectable antibodies in some patients might decrease over time when using certain tests. CDC’s seroprevalence surveys are not designed to provide information on how long antibodies last in people’s body following infection.

Seroprevalence surveys undertaken with commercial laboratories began in 10 sites that reported early community transmission of SARS-CoV-2 in the United States. Commercial laboratory seroprevalence surveys have now been expanded to all 50 states, the District of Columbia, and Puerto Rico. CDC is also conducting a nationwide seroprevalence survey among people who donate blood.

In interpreting the seroprevalence survey results, it is important to note that these results might not be generalizable nationwide because people who donate or submit blood for laboratory tests might be different from the general population. In addition, survey estimates might be affected by false-positive test results (the test result is positive, but the person does not really have antibodies to SARS-CoV-2) or false-negative test results (the person has antibodies to SARS-CoV-2, but the test doesn’t detect them).