Coronavirus antibody tests, which could show some amount of immunity to COVID-19, will be a key part of understanding how much the virus has spread.
Much of the discussion around coronavirus testing concerns the type of test that requires a long swab to go deep in your nose so you can find out, eventually, if you have the virus. These tests are helpful at diagnosing patients but less helpful at assessing the spread of the virus. For that, experts have called for antibody tests. What is an antibody test and why would it help? Here’s what we know:
Antibody tests, also known as serological tests, look for antibodies in a patient’s blood. People who have gotten sick and recovered from COVID-19 have these antibodies, as do those who had the virus without ever experiencing symptoms. Some antibody tests, which require a quick finger prick, can return results in as soon as 15 minutes.
An antibody test is not meant to detect an active infection, as it can take ten days or more for coronavirus antibodies to become detectable in a blood sample after someone has recovered.
As of the end of April, only two kinds of tests are being used to detect active COVID-19 infections, both by looking for the virus’s genetic material in samples obtained by either a PCR (nose swab) test or, in places where it is available, a saliva test.
As Dr. Anthony Fauci said on April 10, these tests will help health officials better understand how many people have been infected with COVID-19.
“As we look forward, as we get to the point of at least considering opening up the country as it were, it’s very important to appreciate and to understand how much that virus has penetrated this society,” Fauci said. “It’s very likely that there are a large number of people out there that have been infected, have been asymptomatic, and did not know they were infected.”
The tests could detect people with some amount of immunity to COVID-19, which, theoretically, might allow them to reenter the workforce without concern that they’ll get sick or infect anyone else, but there is still an active debate about that. The tests could also indicate who has not been exposed to the virus and remains at risk.
From a public-health perspective, results of these tests could change, or confirm, what is known about the virus’s spread, particularly since the U. S. has struggled to increase its testing capacity, making it likely that a still-unknown number of coronavirus cases have gone undetected. More than a million confirmed cases of COVID-19 have been detected in the U. S. so far; if antibody tests reveal that, say, 4 million people have actually had the virus, that would be very valuable information for public-health officials.
Not necessarily. The presence of antibodies only indicates that someone has had COVID-19, but it does not guarantee that person can’t become reinfected with the disease. And even if they are protected, it’s not clear how long that protection will last.
On April 24, the WHO cautioned that “no study has evaluated whether the presence of antibodies to SARS-CoV-2 confers immunity to subsequent infection by this virus in humans,” and recommended against the use of the tests as the basis for any kind of immunity certificate.
