The presence of antibodies to the SARS-CoV-2 virus in your blood shows that you have had previous exposure to that virus or have received a vaccine against it. Antibodies remember the virus and recognize it should a person have a subsequent exposure. Because many of us have not yet been exposed to SARS-CoV-2, our immune systems have no way to fight it off.
Even if we do have antibodies for SARS-CoV-2, it may not be enough to fight a second infection. At this time, we do not know the degree to which people with coronavirus antibodies are safe from catching COVID-19 two or three times. Nor are we certain, if antibodies are present, how long this protection will last. Research to answer these questions is still ongoing.
Antibody testing uses a small blood sample to check for antibodies in the immune system as an indicator of a past infection. If the test results are negative a past infection did not occur. It is also possible that an infection occurred more than four months ago, and insufficient antibodies remain to show up on the test. The results of an antibody test do not confirm whether or not the individual is currently infected.
Antibody testing should not be performed before 18 days following a COVID-19 infection. This is because it typically takes between 10-18 days after infection for antibodies to develop in a large enough quantity to give a positive result. Even if an individual has a positive antibody test, this does not guarantee that they will not become infected again.
Antibody test kits for employees, students, and business owners work by taking a small sample of blood by pricking a finger. This is then mixed with a substance that recognizes one or both SARS-CoV-2 antibodies. These are:
Typically, IgG antibodies develop around 14 days after the onset of COVID-19 symptoms. As far as we currently know, they can stay in the blood for up to four months.