Important update: Healthcare facilities
CDC has updated select ways to operate healthcare systems effectively in response to COVID-19 vaccination. Learn more
To maximize protection from the Delta variant and prevent possibly spreading it to others, get vaccinated as soon as you can and wear a mask indoors in public if you are in an area of substantial or high transmission.
UPDATE
Given new evidence on the B.1.617.2 (Delta) variant, CDC has updated the guidance for fully vaccinated people. CDC recommends universal indoor masking for all teachers, staff, students, and visitors to K-12 schools, regardless of vaccination status. Children should return to full-time in-person learning in the fall with layered prevention strategies in place.
UPDATE
The White House announced that vaccines will be required for international travelers coming into the United States, with an effective date of November 8, 2021. For purposes of entry into the United States, vaccines accepted will include FDA approved or authorized and WHO Emergency Use Listing vaccines. More information is available here.

Test for Past Infection

Test for Past Infection

Antibody or serology tests look for antibodies in your blood that fight the virus that causes COVID-19.

  • Antibodies are proteins created by your immune system that help you fight off infections. They are made after you have been infected or have been vaccinated against an infection.
  • Vaccination is a safe, effective way to teach your body to create antibodies.
  • Antibodies can protect you from getting those infections for some period of time afterward. How long this protection lasts is different for each disease and each person.­
  • Antibody tests should generally not be used to diagnose a current infection with the virus that causes COVID-19. An antibody test may not show if you have a current infection because it can take 1 to 3 weeks after the infection for your body to make antibodies.

Effect of vaccination

  • COVID-19 vaccines teach your body to produce antibodies to fight infection from the virus that causes COVID-19. If you get an antibody test after receiving a vaccine, you might test positive by some (but not all) antibody tests. This depends on which type of antibody the specific test detects.
  • Antibody testing is not currently recommended to determine if you are immune to COVID-19 following COVID-19 vaccination. Antibody testing should also not be used to decide if someone needs to be vaccinated.  CDC’s Interim Guidelines for COVID-19 Antibody Testing provide more information on how antibody testing should be used and interpreted.

Whether you test positive or negative for COVID-19 antibodies using an antibody test, you still should take steps, including getting vaccinated, to protect yourself and others.

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Coronavirus Self-Checker

A tool to help you make decisions on when to seek testing and medical care.

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How to get an antibody test

Decisions about testing are made by state or localexternal icon health departments or healthcare professionals.

Antibody tests for COVID-19 are available through healthcare professionals and laboratories. Check with your healthcare professional to see if they offer antibody tests and whether you should get one.

What do your results mean?

If you test positive

  • A positive antibody test result shows you may have antibodies from a previous infection or from vaccination for the virus that causes COVID-19.
  • Some antibodies made for the virus that causes COVID-19 provide protection from getting infected. CDC is evaluating antibody protection and how long protection from antibodies might last. Cases of reinfection and infection after vaccination have been reported, but remain rare. But getting vaccinated, even if you have already had COVID-19, can help your body make more of these antibodies.
  • You may test positive for antibodies even if you have never had symptoms of COVID-19 or have not yet received a COVID-19 vaccine. This can happen if you had an infection without symptoms, which is called an asymptomatic infection.
  • Sometimes a person can test positive for SARS-CoV-2 antibodies when they do not actually have those specific antibodies. This is called a false positive.
  • Talk with your healthcare professional about your test result and the type of test you took to understand what your result means. Your healthcare professional may suggest you take a second type of antibody test to see if the first test was accurate.

If you test negative

  • You may not have COVID-19 antibodies. This could be because you have not had an infection with the virus that causes COVID-19 or have not received a COVID-19 vaccine.
  • Some antibody tests will only detect antibodies from infection, not from vaccination with the virus that causes COVID-19.
  • You could have a current infection, been recently infected, or been recently vaccinated. It typically takes 1 to 3 weeks after infection or vaccination for your body to make antibodies. If you are infected, you may get sick and spread the virus before you develop antibodies.
    • Some people may take even longer to develop antibodies, and a small portion of people who are infected or vaccinated may never develop antibodies.
  • Sometimes people test negative for SARS-CoV-2 antibodies when they have those specific antibodies. This is called a false negative.
  • Talk with your healthcare professional about your test result and the type of test you took to understand what your result means.

If you have symptoms of COVID-19, you should get a viral test to detect a current infection, even if you were previously infected or vaccinated.

Until we know more, continue to take steps including getting vaccinated to protect yourself and others.

Learn more about using antibody tests to look for past infection.

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For healthcare professionals

For CDC interim guidance on antibody testing in clinical and public health settings, see Interim Guidelines for COVID-19 Antibody Testing.