Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission.
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.
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.

CDC Seroprevalence Survey Types

CDC Seroprevalence Survey Types
Updated Jan. 27, 2021

CDC is collaborating with public health and private partners on a variety of 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 information about COVID-19.

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Large-scale Geographic Seroprevalence Surveys

The largest surveys that CDC is conducting are called “large-scale geographic seroprevalence surveys.” These surveys are being conducted in locations across the United States and are first focusing on areas highly impacted by COVID-19, such as Washington State and New York State, including New York City. Large-scale surveys may perform serology testing on additional blood samples that were originally used for other purposes (e.g., routine cholesterol test). No names are linked to the blood samples used in these surveys. This means the identity and privacy of people whose blood is tested is protected. One limitation of these surveys is that people tested are not necessarily representative of the population for that area.

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Community-level Seroprevalence Surveys

These surveys cover smaller areas than a “large-scale geographic survey.” They sample from select counties, and within this area, the selection of participants is completed in a systematic way. This allows for a more representative population to be tested where results might apply to other similar populations. CDC is working with state and county health departments to learn more about how COVID-19 is spreading in communities by performing serology tests in households in various communities.

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Special Populations Seroprevalence Surveys

These seroprevalence surveys answer questions about specific populations, such as healthcare workers or pregnant people. Because they examine samples from a specific population, their findings cannot necessarily be applied to other populations. However, such surveys can help answer important questions about the risk of infection within specific populations.


Frequently Asked Questions: Learn more about laboratory testing including if you should be tested, where to get tested, and other basics on COVID-19 diagnostic and serology testing.