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Having antibodies to the novel coronavirus is not the same thing as having immunity to COVID-19

CLAIM: A positive antibody test can prove that you are immune to SARS-CoV-2, the novel coronavirus that causes COVID-19.

UNCERTAIN. Antibodies in your blood show that your body has fought an infection caused by the novel coronavirus. But having a positive antibody test has not yet been proven to tell you with certainty that you are immune to being infected a second time.

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Antibodies fight germs that make you sick.

Antibodies are proteins that the body’s immune system makes when it detects a germ inside the body. Antibodies bind to the germ to stop it from spreading throughout your body, and they help your body destroy it. After the antibodies form, they may stay in your body, even after the germ is gone, to protect you against getting infected by the same germ again.

Antibodies are made to fight specific germs. For example, the antibodies your body creates to fight the seasonal flu are different from the antibodies it creates to fight strep throat. Because of these differences, antibodies found in a blood test can tell doctors which germs you have been exposed to in the past.

 
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We are still learning about the level of protection antibodies provide against getting COVID-19 a second time.

When someone is exposed to the novel coronavirus, the body makes several types of antibodies to fight it off. Scientists are working to figure out:

  • How long the antibodies stay in the body
  • Which types of antibodies are needed to fight a second infection
  • How high the level of those antibodies needs to be in the blood to protect against getting COVID-19 again

If antibodies for the novel coronavirus do protect you from getting COVID-19, it is unclear whether this protection lasts for a long time or only for a few months. Studies of SARS—a disease caused by a virus closely related to the novel coronavirus—found that antibody levels declined over time. That means the longer since infection, the less resistant a person was to a second infection.

 
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Even though we still have a lot to learn about antibodies, knowing whether people have antibodies provides important information.

Blood tests for antibodies to the novel coronavirus may not be able to tell us much yet about immunity to a second infection, but they do provide useful information for stopping the spread of COVID-19. Antibody test results help public health officials track outbreaks. Antibodies take time to develop, so if test results from a particular place show that many people have antibodies to the novel coronavirus, it means that an outbreak has happened. Because so many people who have COVID-19 do not have symptoms, antibody test results can tell public health officials if an outbreak of the disease was larger than it originally seemed in a given place.

Researchers also use antibody tests to study treatments and vaccines. The results of antibody tests can help scientists figure out which specific antibodies provide protection against COVID-19. That in turn helps them know whether convalescent plasma—blood with antibodies from someone who has recovered from an infection—can possibly help someone who is currently sick. It also helps scientists identify which antibodies a vaccine needs to produce to provide protection.

 
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The best time to test for antibodies is 2 weeks after COVID-19 symptoms are gone.

Antibodies to the novel coronavirus take at least 1 week to develop and may not be identifiable in a blood test until 3–4 weeks after someone has been exposed to the virus. If you currently have symptoms of COVID-19 or think you may have been exposed to the virus within the past 2 weeks, you need a diagnostic test to tell if you are infected right now.

 

Published on: May 12, 2020