The FDA says current antibody tests shouldn't be used to determine immunity from Covid-19, especially after vaccination. In a recently published message, the agency says misinterpreted results could be harmful.
Guidance on the use and reliability of antibody tests can be confusing.
The FDA says the antibody test results can help identify people who have had a Covid-19 infection.
However, virologists point out that many people successfully fight off Covid-19 without developing any measurable antibodies at all.
Read the FDA message in full below.
The U.S. Food and Drug Administration (FDA) is reminding the public and health care providers that results from currently authorized SARS-CoV-2 antibody tests should not be used to evaluate a person’s level of immunity or protection from COVID-19 at any time, and especially after the person received a COVID-19 vaccination.
While a positive antibody test result can be used to help identify people who may have had a prior SARS-CoV-2 infection, more research is needed in people who have received a COVID-19 vaccination. Currently authorized SARS-CoV-2 antibody tests have not been evaluated to assess the level of protection provided by an immune response to COVID-19 vaccination. If antibody test results are interpreted incorrectly, there is a potential risk that people may take fewer precautions against SARS-CoV-2 exposure. Taking fewer steps to protect against SARS-CoV-2 can increase their risk of SARS-CoV-2 infection and may result in the increased spread of SARS-CoV-2.
The FDA is providing additional information and recommendations to the public and health care providers about the use of antibody tests in people who received a COVID-19 vaccination.
Recommendations for People Who Had or May Have a SARS-CoV-2 Antibody Test
- Be aware that SARS-CoV-2 antibody tests help health care providers identify whether someone has antibodies to SARS-CoV-2, the virus that causes COVID-19, indicating a prior infection with the virus. However, more research is needed to understand the meaning of a positive or negative antibody test, beyond the presence or absence of antibodies, including in people who received a COVID-19 vaccination, in people who have been exposed and have SARS-CoV-2 antibodies, and in people who are not fully vaccinated.
- If you have not been vaccinated: Be aware that a positive result from an antibody test does not mean you have a specific amount of immunity or protection from SARS-CoV-2 infection. If you have a positive test result on a SARS-CoV-2 antibody test, it means that it is possible you were previously infected with the SARS-CoV-2 virus. Talk with your health care provider about the meaning of your SARS-CoV-2 antibody test results.
- If you received a COVID-19 vaccination: Continue to follow the CDC’s recommendations for fully vaccinated people. Be aware that if you have a positive test result on a SARS-CoV-2 antibody test, it is possible you were previously infected with SARS-CoV-2. A COVID-19 vaccination may also cause a positive antibody test result for some but not all antibody tests. You should not interpret the results of your SARS-CoV-2 antibody test as an indication of a specific level of immunity or protection from SARS-CoV-2 infection. Talk to your health care provider or your state and local health departments if you have questions about whether an antibody test is right for you.
Recommendations for Health Care Providers
- At this time, do not interpret the results of qualitative, semi-quantitative, or quantitative SARS-CoV-2 antibody tests as an indication of a specific level of immunity or protection from SARS-CoV-2 infection after the person has received a COVID-19 vaccination. While a positive antibody test can indicate an immune response has occurred (seroconversion), and failure to detect such a response may suggest a lack of immune response, more research is needed. Currently authorized SARS-CoV-2 antibody tests are not validated to evaluate specific immunity or protection from SARS-CoV-2 infection. SARS-CoV-2 antibody tests should be ordered only by health care providers who are familiar with the use and limitations of the test. For more information about antibody tests for SARS-CoV-2, see Serology/Antibody Tests: FAQs on Testing for SARS-CoV-2.
- Be aware that vaccines trigger antibodies to specific viral protein targets. For example, currently authorized COVID-19 mRNA vaccines induce antibodies to the spike protein and not to nucleocapsid proteins that are likely detected only after natural infections. Therefore, COVID-19 vaccinated people who have not had previous natural infection will receive a negative antibody test result if the antibody test does not detect the antibodies induced by the COVID-19 vaccine. If you are considering antibody testing in vaccinated individuals, follow the Centers for Disease Control and Prevention’s guidelines for antibody testing. For more information about antibody test performance visit EUA Authorized Serology Test Performance.
Potential Risks of Improperly Using SARS-CoV-2 Antibody Test Results
Antibodies are proteins created by your body’s immune system soon after you have been infected or vaccinated. SARS-CoV-2 antibody or serology tests look for antibodies in a blood sample to determine if an individual has had a past infection with the virus that causes COVID-19. These types of tests cannot be used to diagnose a current infection. For more information about antibody testing, see Antibody (Serology) Testing for COVID-19: Information for Patients and Consumers.
Test results from currently authorized SARS-CoV-2 antibody tests should not be used to evaluate a person’s level of immunity or protection from COVID-19. If the results of the antibody test are interpreted as an indication of a specific level of immunity or protection from SARS-CoV-2 infection, there is a potential risk that people may take fewer precautions against SARS-CoV-2 exposure. Taking fewer precautions against SARS-CoV-2 exposure can increase their risk of infection and may result in increased spread of SARS-CoV-2.