The optimism that has sent many vaccinated Americans back out into the world is nevertheless mixed with concern about the swift and widespread rise of COVID-19 variants. As a result, some people are requesting antibody tests to determine whether or not their vaccines are effective, and to estimate their level of risk. According to experts, this is not a good idea.

What is an antibody test?

When your body is infected with the coronavirus, your immune system generates antibodies against the nucleocapsid (the protein shell of the virus that houses its genetic material) and the spike proteins that latch onto your body’s receptors. Antibody tests are blood tests that detect whether or not you have been exposed to a particular virus, specifically whether or not you had been infected with the virus and fought it off, and it could differentiate between COVID-19 and the flu or another virus with similar symptoms.

Antibodies generally appear between one and two weeks following an infection, although it’s unclear how long they stay in your body (various studies suggest three to eight months) or how much immunity they provide.  The tests are useful for determining if you had a recent infection, but their use following vaccination is limited.

What an antibody test can’t tell you

The Food and Drug Administration (FDA) has approved 42 antibody tests for emergency use since the beginning of the pandemic. Not all of these tests are precise and consistent enough to render accurate, useful interpretation, however. “We don’t have a tremendous amount of experience with them to know how they correlate with protection,” said Dr. Jesse Goodman, former director of the FDA’s Center for Biologics Evaluation and Research and current senior scholar with the O’Neill Institute for National and Global Health Law.

According to the FDA, a lack of antibodies detected does not mean that a vaccinated person did not have a protective immune response. The COVID-19 vaccines train immune cells to identify and attack the virus’ spike protein. Antibody tests may only seek antibodies that are produced after a natural infection. “Therefore, COVID-19 vaccinated people who have not had previous natural infection will receive a negative antibody test result if the antibody test does not detect the antibodies induced by the COVID-19 vaccine,” the agency warns.

Antibody tests are not one-size-fits-all

Health experts warn that neither vaccines nor antibody tests work the same way for everyone, and misinterpreting test results can potentially cause either needless worry or a dangerous relaxation of precautions. 

One group at particular risk for post-vaccine antibody test inaccuracies are people with compromised immune systems. For someone whose immune system doesn’t function optimally due to either a health condition that affects the system directly or a treatment that suppresses it, the process of training immune cells with a vaccine may not be successful, even if antibodies are present.

The new Centers for Disease Control and Prevention guidelines carry the stipulation that “If you have a condition or are taking medications that weaken your immune system, you may NOT be fully protected even if you are fully vaccinated. Even after vaccination, you may need to continue taking all precautions,” which include wearing a mask. Talk to your healthcare provider for guidance.

How can I know my vaccine is working?

Clinical trials and real-world data have shown, and continue to confirm, that the Pfizer and Moderna vaccines are more than 90% effective at preventing infection from the SARS-CoV-2 coronavirus, and the Johnson & Johnson vaccine is more than 70% effective. 

Several studies are investigating whether or not people with compromised immune systems can get a stronger response either through a series of booster shots or by other methods. Findings from these studies are expected later this year.

Research is also being done to better understand and predict who is most at risk for a low antibody response and how that can be remedied. In the meantime, said Goodman, people should continue getting vaccinated, but not bother trying to determine their vaccine’s effectiveness with an antibody test. “It’s not recommended,” he said.

*Santhanam, L. (2021, June 1). Why You Shouldn’t Get a COVID Antibody Test After a Vaccine. PBS Newshour. https://www.pbs.org/newshour/health/covid-antibody-test-after-vaccine 

Much about the novel coronavirus, i.e., COVID-19, is still not fully understood. As research progresses and our knowledge of the virus increases, information can change rapidly. We strive to update all of our articles as quickly as possible, but there may occasionally be some lag between scientific developments and our revisions.