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A Centers for Disease Control and Prevention panel reminded consumers again this week not to use commercial antibody tests to check whether or not they are immune to COVID-19. These tests, the panel said Thursday, are inconsistent and cannot be used to measure protection against the virus.
Antibody tests are primarily used to determine if a person has ever been infected with the COVID-19 virus. Early reports suggested that people who tested positive for antibodies after a known or asymptomatic infection had some level of immunity. Now, most health officials agree that having a positive antibody test does not mean a person is safe from contracting the virus.
“After a while the antibodies start to drop again, that’s not a bad thing,” said Dr Todd Ellerin, director of infectious diseases at South Shore Health. But the presence of antibodies is only part of the story when it comes to immunity.
“Your antibodies are only one part of the immune system. You also have other parts of the immune system, such as T cells,” Ellerin said. “The response of T cells is probably very important in protecting against serious disease because they can attack the virus directly.”
With highly publicized breakthrough infections among sports teams and Olympians, many are wondering if they still have the same level of protection against the delta variant as when they first received their shots.
But scientists are still looking for a so-called “correlate of protection” – a marker in the blood that would reliably indicate protection. And they don’t necessarily think they’re antibodies. This means that the presence of antibodies – or even more specific antibody levels – doesn’t necessarily correlate with a person’s level of protection.
“Correlates of protection are not known, so it is not known whether a positive antibody test after infection with COVID-19 represents protection against a variant, including the delta variant,” said Dr Dan Barouch. , director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center.
The Food and Drug Administration strongly warns against antibody testing as a way to check immunity in fully vaccinated people, writing in May that “currently permitted antibody tests against SARS-CoV-2 should not be used to assess a person’s level of immunity or protection against COVID-19 at any time, and especially after the person has been vaccinated against COVID-19. ”
Experts agreed that this warning could be confusing for some consumers. After all, antibody tests are routinely done to test for immunity against other viruses such as hepatitis B, measles, mumps, rubella, and chickenpox.
But COVID-19 is different, experts said.
“It is generally not recommended to use commercial antibody tests to monitor vaccine responses, as the significance of these tests has not been well defined as to whether or not they can predict vaccine protection.” , said Barouch.
We know that COVID-19 vaccines work not because of a blood test, but from large clinical trials that compared a group of unvaccinated people to a group of vaccinated people, finding that unvaccinated people were extremely likely to be infected and become seriously ill with COVID-19[FEMININE[FEMININE
“What we generally think is that all vaccines get you to high enough levels that even if they go down, you’re still protected from hospitalization,” Ellerin said. “Because the vaccines have done a great job, all of them, at preventing hospitalizations, we believe, based on some modeling studies, that you only need 3% of your average neutralizing antibody response to prevent yourself to go to the hospital. “
Unfortunately, there is no commercially available antibody test that can tell us whether we are truly immune to COVID-19 or how long any immunity acquired through natural or vaccine-mediated infection will last.
According to the CDC and the FDA, the only acceptable time to use an antibody test to check for immunity is if you have volunteered for a carefully monitored clinical study. Some people who are immunocompromised, such as cancer or autoimmune diseases, do not respond well to vaccines.
People with this medical condition are monitored for antibody levels using very specific antibody tests and under the close supervision of doctors. And early data suggests that for some, a third hit might help.
No vaccine is 100% effective in preventing infections, but health officials continue to recommend vaccination as the best way to prevent COVID infections.
“Even if we find a correlate of immune protection, we want it to have clinical relevance, not just in vitro or test-tube relevance,” Ellerin said. “National guidelines and I don’t recommend antibody testing for the general public, but for immunocompromised patients, that’s another story.”
Odelia N. Lewis, MD is a recent graduate of the SUNY Downstate Family Medicine Residency Program and an ABC News Medical Unit Contributor.
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