Last year, antibody tests got a lot of attention, as people wanted to figure out if they’d had COVID-19 and whether or not they were protected from the virus. Now, antibody tests are back in the spotlight; this time related to vaccine protection.
Can an antibody test prove whether or not you’re protected by the COVID-19 vaccines?
- Dr. Emily Ricotta, infectious disease epidemiologist at National Institutes of Health
- Dr. Amesh Adalja, infectious disease physician and senior scholar at Johns Hopkins Center for Health Security
- Dr. Brian Boyarsky, research fellow at Johns Hopkins Medicine
- Dr. Alexander Huang, Assistant Professor of Medicine, Perelman School of Medicine, University of Pennsylvania
- U.S. Food and Drug Administration (FDA)
No, antibody tests cannot prove whether or not you’re protected by the COVID-19 vaccines.
WHAT WE FOUND
Experts believe antibody tests are a key part of protection from COVID-19. Recent studies show a direct connection between antibody level and COVID-19 immunity.
“Not only are you producing many antibodies, but those antibodies are then able to actually neutralize the virus, which is what we need them to do,” Dr. Emily Ricotta said.
Dr. Ricotta is leading a study on vaccine response among immunocompromised patients at the National Institutes of Health. She says testing individuals for COVID-19 immunity is far more complicated.
“Because we don’t know what these results really mean,” she explained.
A key concern centers on the "correlate of protection": the number of antibodies the average person needs to be protected from COVID-19. Right now, experts don’t know that number, and commercial antibody tests only offer vague information on a patient’s levels.
“So, we can’t just say, ‘You have antibodies, ergo you’re protected,’” Dr. Ricotta explained. “Nobody knows what that means yet. So we don't want people to change their behavior, thinking, ‘Oh, I'm totally protected,’ when you may not actually be.”
On the flip side, experts warn that people with low levels of antibodies may still be protected by COVID-19 vaccines, because antibodies are just one piece of the protection puzzle.
On top of antibodies, experts say the average person should also produce T cells in response to the COVID-19 vaccines. The antibodies prevent people from ever getting COVID-19, and T cells keep them from getting sick once infected with the virus.
Even with no antibodies, experts say it’s possible a person could have enough T cells to be protected from COVID-19.
“That's equally important when it comes to a vaccine response,” Dr. Amesh Adalja said. “There's a reason to be worried if you don't have antibodies after a vaccine. But it's not the whole picture, you'd have to couple that with knowledge about the person's T-cell reactivity.”
T-cell tests exist, but they’re harder to come by than antibody tests. And, similar to antibodies, experts don’t have a correlate of protection for T cells, meaning they don’t know how many the average person needs to be immune from COVID-19.
“I think we need a lot more data to understand what the phenomenon is that's going on,” Dr. Adalja said.
The FDA does not recommend people test their antibody level to assess COVID-19 immunity after vaccination.
“While a positive antibody test result can be used to help identify people who may have had a prior SARS-CoV-2 infection, more research is needed in people who have received a COVID-19 vaccination,” the FDA said in a release. “Currently authorized SARS-CoV-2 antibody tests have not been evaluated to assess the level of protection provided by an immune response to COVID-19 vaccination. If antibody test results are interpreted incorrectly, there is a potential risk that people may take fewer precautions against SARS-CoV-2 exposure.”
But antibody tests are being used in select cases. Some doctors are testing immunocompromised patients after vaccination to better advise them.
“Obviously, it doesn't measure everything, but it just gives you a guide of how strong their response to the vaccine was,” Dr. Victoria Shanmugam said.
Dr. Shanmugam is the director of rheumatology at George Washington University and treats patients with a range of autoimmune diseases.
“I've had patients with really zero antibody response after being vaccinated,” she said. “I would have to assume that those patients are still as vulnerable as a non-vaccinated individual.”
She’s advising patients who show low levels of antibodies to remain vigilant and exercise safety measures like masks and distancing.
But even that testing strategy is being debated.
Dr. Brian Boyarsky is a research fellow at Johns Hopkins studying antibody levels in immunocompromised patients.
“I do think that’s a reasonable approach,” Dr. Boyarsky said about testing immunocompromised patients to better advise them. “It's much more information to know that someone doesn't have any antibodies at all. But even if somebody has a modicum of a level, we still don't know what level of protection is offered to that person.”
Dr. Adalja is skeptical of offering clinical advice to immunocompromised patients based on antibody tests at this point.
“I don’t think we have a strong enough evidence base to recommend this,” Dr. Adalja said. “It's fine if they want to do it, but I would do it with the caveat that it's unclear what it actually means.”
Research teams across the country are now studying vaccine response, looking at both antibodies and T cells.
Researchers at Penn Medicine are studying T cells in blood cancer patients, whose immune systems are compromised and antibody levels are lower than normal. Their early data indicates patients can fight off COVID-19 with T cells. Dr. Alexander Huang authored the study.
“We now suspect that these patients would benefit somewhat from the enhanced T cell responses [to a COVID-19 vaccine], but that has to be tested rigorously in the population,” Dr. Huang said.
He’s hoping new research on T cells will eventually reveal a correlate of protection and help doctors guide vulnerable patients.
“If we are able to say you have this degree of T cells, either presence or absence, or even better, 80% or 100%, of what is expected, then the patient will get some degree of understanding of the risk and protection and it can inform on how they lead life,” Dr. Huang said.
He hopes, in the next few months, experts will know much more about how to measure protection from COVID-19.
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