Antibody tests have offered hope for progress against the coronavirus because they may help understand the outbreak and help society return to normal.
Studies of the tests, which look for COVID-19 antibodies that indicate a person has recovered from the virus, have ramped up this month.
The National Institutes of Health announced that it would begin recruiting as many of 10,000 volunteers for a study of the tests, and Major League Baseball said its employees would participate in a similar study conducted by Stanford University.
The Centers for Disease Control and Prevention also began a preliminary study of antibodies this month.
Here’s what you need to know about antibody testing.
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Q. What is an antibody test?
A. When you recover from a virus, cells in your immune system “remember” it to help the body the next time you’re sick. Antibodies help fight off the infection when the virus enters your body, making you immune.
An antibody test, which is also called a serology test, looks for evidence your immune system has responded to the virus before.
Typically, the test looks for two types of antibodies, IgM antibodies, which are produced early on in an infection, and IgG antibodies, which appear after you have recovered. IgG antibodies generally stay in the body much longer than IgM antibodies.
To test for antibodies, you have to give a blood sample, usually with a finger prick.
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Q. If I have antibodies, am I immune to the coronavirus?
A. There’s still a lot doctors don’t know about immunity to COVID-19.
Although the presence of antibodies indicates your immune system has responded to the virus, scientists don’t know how long that immunity will last or how effective it is.
Health experts say it’s possible some people will develop a stronger immune system response than others, and it’s not known whether the novel coronavirus behaves the same way as the common cold, another strain of coronavirus that doesn’t lead to lasting immunity.
It’s possible COVID-19 may behave like two other strains that have caused outbreaks, SARS and MERS, which some health experts believe gives infected people immunity for about a year.
“If we look at MERS coronavirus, we would see people who would have an antibody response for maybe 10 months, maybe a year,” Dr. Maria van Kerkhove, the World Health Organization technical lead for the COVID-19 response, told CNN. “Even there, we didn’t know if that conferred protection. So for … (COVID-19), the answer is we don’t know yet, but those studies are being done.”
It’s possible the novel coronavirus could mutate over time, making antibodies to the current form of the virus useless.
For now, health experts think the presence of COVID-19 antibodies probably provide some protection for some amount of time.
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Q. How accurate are the tests?
A. The U.S. Food and Drug Administration relaxed its rules for COVID-19 tests in February, allowing companies to develop them more quickly. Since then, it has approved only one antibody test, which is made by the company Cellex.
Health experts have said that without the normal thorough review, many tests are likely to be inaccurate. Scott Becker, CEO of the Association of Public Health Laboratories, told CNN dozens of companies are flooding the market with inadequate tests.
“It’s just deceptive,” Becker said. “They’re selling these tests, but nobody has checked their quality. We need some level of scientific review and rigor on these tests.”
Health experts have said tests that haven’t been thoroughly vetted can produce false positives, giving people the wrong idea that they are immune.
Tests that have high validity can still be wrong more often because the accuracy of the test depends on where they’re being used. A test that is 90% accurate in an area where COVID-19 is widely present can produce a significant number of false positives in a population that hasn’t been as badly affected, health experts say.
“It is kind of a strange thing,” Dr. H. Gilbert Welch, a scientist at Brigham and Women’s Hospital in Boston who studies issues surrounding tests and screening, told National Public Radio. “An antibody test is much more likely to be wrong in a population with very little COVID exposure.”
Also, some health experts say it’s possible an antibody test could mistake another strain of coronavirus, like the common cold, for COVID-19.
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Q. If we don’t know that much about immunity, how can tests help?
A. Antibody tests can help health officials and researchers know how common the virus is. The tests may be especially useful for finding out who had the virus without knowing it, because they had mild symptoms or no symptoms at all.
Public officials hope that the tests can be used to help determine who can return to work safely.
Also, the presence of antibodies can help with experimental treatments for COVID-19 in which antibodies from a person who has recovered are injected into a person who is sick.
There are questions about how effective that treatment will be, but some companies have begun collecting plasma to treat sick patients.
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Q. Where can I get an antibody test?
A. COVID-19 antibody tests aren’t widely available yet. Health experts say it probably will be several weeks before there are more of them, and even then they may be reserved for health care workers and other first responders.
Health experts recommend contacting your doctor to see whether it’s possible for you to be tested.
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