The Centers for Disease Control and Prevention (CDC) is partnering with commercial laboratories to conduct a large-scale geographic seroprevalence survey that has tested de-identified clinical blood specimens from Connecticut, South Florida, the New York City metro area, Missouri, Utah and Western Washington State for SARS-CoV-2 antibodies.
The CDC, in partnership with state and local health departments, plans to publish results from the expanded seroprevalence survey in an additional four states including California, Louisiana, Minnesota, and Pennsylvania.
The survey includes people who had blood specimens tested for reasons unrelated to COVID-19, such as for a routine or sick visit during which blood was collected and tested by commercial laboratories in participating areas from each of the 10 sites. The CDC aims to test about 1,800 samples collected from each of these 10 areas, approximately every three–four weeks. Researchers are looking to see what percentage of people tested already have antibodies against SARS-CoV-2, and how that percentage changes over time in each area.
The CDC has received results from the Western Washington State region; the New York City metro region; south Florida; and all of Connecticut, Missouri, and Utah from blood samples collected by commercial laboratories as part of routine patient care.
There are limitations of this survey that should be considered when interpreting the results.
· People who have blood taken for routine screening or sick visits may not represent people from the total population in an area.
· Some results may be false positive results (the test result is positive, but the person does not really have antibodies to SARS-CoV-2), or false negative results (the person has antibodies to SARS-CoV-2, but the test doesn’t detect them). False positive results are more likely change the survey results if it is an area where the percentage of individuals previously infected is relatively low; it could make it look like more people are infected in the community than really are.
The analysis adjusted the seroprevalence estimate to account for false positives and false negatives.
Results from seroprevalence surveys should not be interpreted to mean that people who have tested positive for having SARS-CoV-2 antibodies are immune. They do not know whether having SARS-CoV-2 antibodies provides protection against getting infected again. Other studies are planned to learn more about SARS-COV-2 antibodies, including how long they last, whether or not they provide protection against getting infected again, and if you get infected again, whether or not they can make that illness milder.
While some seroprevalence surveys can look at risk factors for infection, such as a person’s occupation or underlying health conditions, this seroprevalence survey was not designed to be able to provide that information. This survey will help us better understand the percentages of people who were previously infected with SARS-CoV-2 in the areas studied (that is called seroprevalence).
The CDC also will use this information to estimate the number of people in the areas sampled who have been previously infected with SARS-CoV-2, including those that may not have been reported in official case counts. Some of those people may not have been counted because they had mild illness or no symptoms and did not get medical care or testing.
Finally, some seroprevalence surveys can show how long antibodies last in people’s bodies following infection; this survey was not designed to provide that information.
