Is it true that if you have had Covid and have too many antibodies and take another shot it can cause death? We have been told by the medical community not to take any other shot at this time because of the amount of antibody count in the test.
Antibody tests can’t confirm if you’re protected against COVID-19 after vaccination. Here’s why.
Adrianna Rodriguez, USA TODAY |
People would like to know whether their COVID-19 vaccine is protective enough or a previous infection will keep them safe. Experts warned that taking an antibody test isn’t a good way to find out.
Everyone can receive the COVID vaccine except children under 12, so when can they get it?
The tests were designed to show whether someone was recently infected with the coronavirus – not whether they have enough immune soldiers to prevent an infection.
The level of antibodies needed to provide protection isn’t known. There are nearly 90 different antibody tests on the market, most of which measure something slightly different.
All that means it’s anyone’s guess what the tests actually show about how protected someone is against COVID-19. Taking a test could give people a false sense of security, health experts said, or a load of unnecessary anxiety.
“(Antibody tests) were never developed and designed to detect or tell us anything about vaccine-induced protective immunity,” said Dr. Elitza Theel, director of the Infectious Diseases Serology Laboratory at the Mayo Clinic.
Antibody testing: What’s out there and what it can tell you
The Centers for Disease Control and Prevention and the Food and Drug Administration recommend against using antibody tests to assess immunity after COVID-19 vaccination.
As of Aug. 18, the FDA has authorized nearly 90 different antibody tests, which range in price, to detect previous SARS-CoV-2 infection. Each test varies in which antibodies it detects, how well it detects them and how it reports its results.
“There are so many antibody tests out there that look for antibodies to different antigens,” Theel said. “Their performance characteristics differ … there’s a lot of variability.”
A test’s sensitivity is its ability to recognize antibodies from the virus that causes COVID-19. Antibody tests can range from 85% to 99% sensitivity. Tests vary in specificity, which shows how likely a positive result is accurate.
Not all of them look for the same antibodies. Some tests look for antibodies created from a part of the virus called the nucleocapsid protein.
These antibodies serve only as a marker of previous infection and don’t provide any kind of protection against the virus, said Dr. Reynold Panettieri, professor of medicine at Robert Wood Johnson Medical School in New Brunswick, New Jersey.
“It’s like a smoking gun,” he said. “The bullet is the virus, the smoke from the gun is the nucleocapsid … all it (says) is you’ve gotten an exposure, but it’s not going to help you prevent infection.”
Only antibodies that prevent the virus from entering a cell provide protection from infection.
The COVID-19 vaccines help the body create antibodies to the spike protein – and only the spike protein – which means people who have been vaccinated but not previously infected will show a negative result to a test that detects only antibodies from the nucleocapsid protein.
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Some tests specifically test antibodies to the spike protein, but this can also be deceptive as not all of the antibodies are protective.
Protective antibodies bind to the virus’s spike protein ACE2 receptor and prevent the virus from entering the cell.
“They bind to the virus in a way that they neutralize its ability to infect the cell,” Theel said.
Non-neutralizing antibodies may bind to other parts of the spike protein and have no effect on virus entry. Most tests don’t differentiate between the two types of antibodies.
A test that yields no spike protein antibodies doesn’t necessarily mean a person is unprotected from the virus, said Dr. Daniel Kuritzkes, chief of the division of infectious disease at Brigham and Women’s Hospital.
The body has experience producing those antibodies from the vaccine, he said. Even though there aren’t any detectable at the moment of testing, the body can quickly produce them again if it encounters the virus.
“With any vaccine, the response you measure in the blood is going to decrease over time after vaccination because the body isn’t being constantly exposed to the foreign protein,” Kuritzkes said. “But if they encounter the virus, the body can very rapidly have a recall, or a memory, response that is able to basically rush to the scene of infection and contain it.”
Antibodies don’t necessarily mean protection against COVID-19
Even if all commercial tests were able to detect neutralizing antibodies from COVID-19 vaccines, health experts said, immunity would not be guaranteed as it’s unclear what levels are needed to ensure protection against the virus.
“One of the biggest challenges and the reason why it’s not recommended to do post-vaccination antibody testing is because we still don’t have a defined correlate of protection,” Theel said. “The higher number, the more antibodies you have. But what number is clinically significant and associated with protection? We can’t say, yet.”
A preprint study published Aug. 10 and not yet peer-reviewed sought to answer this question by looking for markers in vaccinated patients’ blood that would indicate immunity. Researchers found higher levels of neutralizing antibodies were linked with higher levels of vaccine efficacy.
Health experts said more studies are needed to confirm the study’s findings.
Measuring antibodies captures only one part of the immune system, Theel said.
T-cells are one of the most important players in cellular immunity. Whereas protective neutralizing antibodies bind to the spike protein to prevent the virus from entering the cell, T-cells search and destroy infected cells where the virus reproduces.
The FDA authorized a test that detects a T-cell immune response to SARS-CoV-2 in March, but it’s not widely available.
“So it would be a mistake for someone to measure an antibody response five or six months after the vaccine as not having immunity because your T-cell response is going to peak at that time, (and) it’s going to be more robust in generating immunity,” Panettieri said.
Kuritzkes said most Americans shouldn’t depend on antibody tests to assess immunity after COVID-19 vaccination, but there are a few exceptions. One includes people who have an immunocompromising condition or take immune suppressing medications.
If a spike protein antibody test yields no antibodies in a person who has a compromised immune system a month after getting fully vaccinated, it’s safer to assume that person did not build a sufficient immune response from the vaccine.
“In that situation, people need to be concerned that they may be susceptible to COVID-19 and should continue to take precautions such as wearing masks when they’re out and about and avoid large gatherings,” Kuritzkes said.
Though most fully vaccinated Americans can assume they have some protection against the virus, Kuritzkes said everyone should practice mitigation measures such as masking and social distancing amid the nationwide spike in coronavirus cases driven by the highly contagious delta variant.
“In the current surge, everybody should be taking precautions regardless of what an antibody test is showing them,” he said.
Follow Adrianna Rodriguez on Twitter: @AdriannaUSAT.
Health and patient safety coverage at USA TODAY is made possible in part by a grant from the Masimo Foundation for Ethics, Innovation and Competition in Healthcare. The Masimo Foundation does not provide editorial input.
This article originally appeared on USA TODAY: Antibody tests can’t confirm if you’re protected against COVID-19 after vaccination. Here’s why.
Confucius is raising his ugly head again.