From the FDA: "At this time, researchers do not know whether the presence of antibodies means that you are immune to COVID-19; or if you are immune, how long it will last.
In people who have received a COVID-19 vaccination, antibody testing is not recommended to determine whether you are immune or protected from COVID-19. and more:
Q: Are antibody tests used to diagnose COVID-19?
A: No. An antibody test does not detect the presence of the SARS-CoV-2 virus to diagnose COVID-19. These tests can return a negative test result even in infected patients (for example, if antibodies have not yet developed in response to the virus) or may generate false positive results (for example, if antibodies to another coronavirus type are detected), so they should not be used to evaluate if you are currently infected or contagious (ability to infect other people).
Q: If antibody tests cannot be used to diagnose COVID-19, what tests are available for that?
A: Currently, there are two types of diagnostic tests for COVID-19:
Molecular (RT-PCR) tests, which detect the virus' genetic material
Antigen tests that detect specific proteins on the surface of the virus
Molecular and antigen tests can detect if you have an active coronavirus infection. If you test positive on either type of test, you should follow the CDC's guidelines to protect yourself and others.
Molecular and antigen tests are performed using samples taken mostly from the nose and throat using a long swab, or other respiratory specimens.
For more information on the different types of tests, see:
Coronavirus Testing Basics
CDC: Testing for COVID-19
Understanding Antibody Test Results
Q: What does a positive antibody test mean?
A: If you have a positive test result on a SARS-CoV-2 antibody test, it is possible that you have recently or previously had COVID-19. There is also a chance that the positive result is wrong, known as a false positive. False positive tests may occur:
Because antibody tests may detect coronaviruses other than SARS-CoV-2, such as those that cause the common cold.
When testing is done in a population without many cases of COVID-19 infections. These types of tests work best in populations with higher rates of infection.
Q: Does a positive antibody test mean that I am immune to COVID-19?
A: A positive antibody test does not necessarily mean you are immune from SARS-CoV-2 infection, as it is not known whether having antibodies to SARS-CoV-2 will protect you from getting infected again. It also does not indicate whether you can infect other people with SARS-CoV-2.
Q: What does a negative antibody test mean?
A: A negative result on a SARS-CoV-2 antibody test means antibodies to the virus were not detected in your sample. It could mean:
You have not been infected with COVID-19 previously.
You had COVID-19 in the past but you did not develop or have not yet developed detectable antibodies. It is unknown if all infected individuals will develop a detectable antibody response.
The result may be wrong, known as a false negative. This occurs when the test does not detect antibodies even though you may have specific antibodies for SARS-CoV-2."
