If you've gotten the COVID vaccine, there may be a tiny voice in the back of your head saying, "What if it didn't work?" The Centers for Disease Control and Prevention (CDC) has reported on breakthrough COVID cases that have infected people who were fully vaccinated—and while the risk is very low, it's normal to feel a bit apprehensive. You may also be worried if you already have a compromised immune system or if you didn't experience some of the common side effects reported after vaccination. But don't go and book an appointment for an antibody test to try to see if the vaccine produced sufficient antibodies to protect you against the coronavirus. Experts say antibody tests can't actually tell you if your COVID vaccine worked—and there are key reasons why.
The CDC does not recommend that you use antibody testing to "assess for immunity" to COVID following vaccination. According to the agency, most antibody tests currently available for COVID look for antibodies that are different from the ones produced by the available COVID vaccines: Moderna, Pfizer, and Johnson&Johnson. Antibody tests that do not detect the specific antibodies induced by these vaccines "will be negative in persons without history of previous natural infection," even if they received one of the three vaccines.
"When most people sign up for [an antibody] test, most laboratories and providers are typically testing for anti-nucleocapsid antibodies," Luis Ostrosky, MD, an infectious disease specialist with University of Texas Physicians, explained in a blog post for the university. "The problem with that is those are not antibodies that would be created by the vaccine, but only through natural infection."
Carl Fichtenbaum, MD, an infectious disease specialist at the University of Cincinnati College of Medicine, told NPR that there are in fact reliable antibody tests to verify antibody protection from vaccines for other diseases, such as the mumps and measles. However, he noted that "those took decades to develop, and with COVID-19 we're only at a year and a half," meaning that scientists haven't had time to develop such a reliable antibody test for the COVID vaccines.
According to Ostrosky, if you are determined to test your immunity, there is one test that scientists are producing to test for the antibodies that COVID vaccines create: a spike protein COVID antibody test. You can try to seek one of these out two weeks after your final dose of the COVID vaccine, but Ostrosky also notes that experts still don't know exactly what correlation exists between the level of these antibodies and your actual immunity to the coronavirus.
In fact, Quest Diagnostics, one of the manufacturers for a U.S. Food and Drug Administration (FDA)-authorized spike protein COVID antibody test, says that its test can detect antibodies from a prior infection, but post-vaccination results are not certain. "Positive results may also occur after a COVID-19 vaccination, but the clinical significance is not yet known, nor is it known how good this test is at detecting antibodies in those who have been vaccinated," the company notes on their website.
"If you get tested for antibodies and the results come back low or with none at all, that does not mean that your vaccination didn't work," Ostrosky said. "You should talk to your doctor about your results."