The Public Health Agency of Sweden
Updated 1 March 2021

An antibody test can show if you have already had COVID-19

An antibody test can show if you have already had COVID-19 and developed antibodies against the virus. Even if you have antibodies, you need to continue to follow the general guidelines on reducing infection in society.

To test if you have had COVID-19, an antibody test is performed by taking a blood sample. It may take time for the body to form antibodies. This means that you should not take the test too early – instead you should wait until 2–3 weeks after you became ill.

Antibodies reduce the risk of becoming infected and infecting other

At present, we estimate that almost everyone who has developed IgG antibodies is protected against reinfection. This means that there is lower risk that you will get infected and become seriously ill. You are also less likely to pass the virus on to others. We estimate that the protection you gain after having COVID-19 lasts at least half a year from when you became ill.

There are people who have other diseases and disorders that cause them to have a compromised immune system. This may mean that they don’t develop the same protection against COVID-19.

It is important to keep in mind that even if you have taken a test that shows that you have COVID-19 antibodies, you still need to continue to follow the general guidelines on preventing infection in society. For example, this means that you should stay at home when you are ill.

Find out what applies to antibody testing where you are

The regions decide who to test, so you need to find out what applies in the region where you are.

You can do this by going to the www.1177.se/covid-19-prov (in Swedish) website and selecting your region.

Some private actors also administer antibody tests and are responsible for all information about the testing and the test results. To provide a reliable result, antibody tests must be of a high quality and properly administered. The person performing the test needs to provide information about how the person being tested should respond to her/his test results.

Not everyone develops measurable antibodies

Some people who have had COVID-19 do not develop measurable levels of antibodies, while others develop antibody levels so high that they can be measured in a blood test. Therefore, a person can have a negative antibody test even though they have actually gone through an infection. Although not everyone who has been ill with COVID-19 develops measurable levels of antibodies in the blood, in the vast majority of cases these people still develop some form of immune response. For example, you may have so-called T-cell immunity to the virus. Analyses of T-cell immunity are more complex to perform than antibody analyses. They are not performed for individuals.