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Why antibody tests have limited use of controlling viral spread

Learn the differences in the three tests available to detect COVID-19.
Graphic of antibodies attacking a disease causing protein from the COVID virus
Graphic of antibodies attacking a disease causing protein from the COVID virus(Terri Russell)
Published: Nov. 26, 2020 at 6:08 AM AKST
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ANCHORAGE, Alaska (KTUU) - Antibody tests can help determine if you had COVID-19 sometime in the past. But its use in managing the spread of COVID-19 is limited, according to the State of Alaska’s public health team.

“If you’ve tested positive for COVID, there are three categories of tests,” Dr. Joe McLaughlin, Alaska’s Chief Epidemiologist said Monday during a press conference over Zoom for reporters.

Two tests are used to test for active, acute infection. The PCR tests look for the genetic material of the virus. While antigen tests look for certain proteins associated with the virus.

“The third category is antibody tests. Antibody tests are not used to test for acute infection. They are used to test for prior infection,” McLaughlin said.

On Nov. 9, Dr. Eliabeth Ohlsen, another member of the state’s public health team, said in a separate Zoom call that “for right now, antibody tests, anything that involves taking blood, is not useful for the questions that we are asking.”

“The only question a blood test, an antibody test can ask, is ‘Do I have something in my blood that looks like what happens after somebody has covid?’ It doesn’t tell you if you are contagious. It doesn’t tell you if you are protected,” Ohlsen said.

That’s because it could be possible to have antibodies and still be infectious within the disease course, or not have the antibodies and still be infectious because your body hasn’t mounted its antibody-producing defense yet.

On Monday, during the same Zoom video call with McLaughlin, Alaska Chief Medical Officer Dr. Anne Zink reiterated that tests are used to prevent infection. Positive test results let people know they need to go into isolation and notify close contacts to go into quarantine. The goal is to interrupt the highly contagious virus’s ability to find human hosts by creating distance between people, along with other intentional precautions to minimize risk.

With vaccines on the way, likely coming out in a few weeks, some patients of COVID have wondered if they need a vaccine, or if their bout with the illness will have left them with enough protective antibodies to be immune.

“The answer is, we don’t know yet. That’s a question we’ve all raised to CDC, and many states have, and CDC has come back and said, ‘We don’t know yet,’” Mclaughlin said.

Scientists are still looking at whether antibodies produced as a result of infection provide protection, and for how long.

McLaughlin said he expects a recommendation could come out for everyone to get the COVID-19 vaccine, as the vaccine will help the body develop antibodies that may be much more robust than those developed during a bout with the illness, especially for individuals who may have been asymptomatic or who experienced only mild symptoms.

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