FDA: Don't Use Antibody Tests to Check if Your COVID Vaccine Worked

Last week, the Food and Drug Administration (FDA) issued guidance saying you shouldn't use antibody tests after your COVID-19 vaccine to measure your level of protection. Healthcare providers use these tests to determine whether someone was previously exposed to SARS-CoV-2, the virus that causes COVID-19. They aren't intended for individuals to assess whether they are protected or not. 

Experts warn that you shouldn't use antibody tests to influence personal decision-making either. It may be an important public health tool, but it has very little use for individuals.

What Are Antibody Tests Used For?

“Antibody tests, or serology tests, are used to detect if someone previously was infected with SARS-CoV-2,” Gigi Kwik Gronvall, PhD, senior scholar at the Johns Hopkins Center for Health Security, tells Verywell. “They aren’t used to find out if someone was currently infected.”

According to the Centers for Disease Control and Prevention (CDC), antibody testing is not recommended for the following:

• To evaluate COVID-19 immunity after vaccination
• To assess the need for vaccination in an unvaccinated person
• To establish the presence or absence of a SARS-CoV-2 infection

In various clinical settings, it is important to know whether someone had COVID-19 in the past, Sheldon Campbell, MD, PhD, professor of laboratory medicine at Yale School of Medicine and associate director of Yale Medicine’s Clinical Microbiology Lab, tells Verywell. 

For instance, healthcare providers can evaluate whether a case of multisystem inflammatory syndrome in children (MIS-C)—a rare but severe medical condition that causes inflammation in vital organs—is associated with previous COVID-19 infection. Determining past infection helps with observing long-term health impacts in adults as well.

It is also necessary when determining whether a donor is eligible for convalescent plasma therapy, the procedure where a recovered COVID-19 patient with SARS-CoV-2-specific antibodies donates plasma to a person with a current infection to boost their immune response. The Food and Drug Administration (FDA) granted this treatment an Emergency Use Authorization (EUA) last year.

“Antibody tests are designed to look for past infection, but the reality is that they have very little utility for individuals,” Gronvall says.

Why Aren’t Antibody Tests Recommended for Personal Use?

Experts do not recommend the individual use of antibody tests for several reasons, including:

• Test results may be inaccurate without multiple sequential testing
• Many antibody tests on the market are substandard and can lead to inaccurate results
• A positive result can bring a false sense of security and give people the impression that safety precautions and public health measures are no longer necessary
• The presence of antibodies may mislead an individual to think they are automatically immune to reinfection

“The tests are not authorized for use to check if the vaccine worked," Gronvall says. "Some of the tests look for a different part of the virus than was used in the vaccine, so you might think you aren’t protected when you are."

Until there's a clearer understanding of the effects of SARS-CoV-2 on the immune system and how antibodies can reflect immunity, antibody testing should remain a tool for public health.

Why Are Antibody Tests Incapable of Checking COVID-19 Immunity?

There isn't enough data yet to be certain that a positive antibody test means protection from COVID-19, or vice versa.

“The immune system has a whole lot of working parts; of which antibody is only one,” Campbell says. “It seems like high levels of antibody are protective, because we can give plasma from people with high levels of antibody to COVID patients and it’s somewhat protective, but that’s a long way from knowing what a positive antibody test means in everyone.”

If immunocompromised people who aren’t protected by antibodies receive a positive antibody test result, they might think they are protected from COVID-19 when they’re not. On the other hand, people who do not produce enough antibodies but have an otherwise functioning immune system may not think they’re protected but actually are.

To put it simply, “we don’t have good data on what antibody tests mean for protection even in the population at large, and definitely not in particularly vulnerable populations,” Campbell says.

According to Gronvall, if you have immune problems where you are less able to benefit from the COVID-19 vaccine, you should discuss with your primary healthcare provider whether you are still likely to be protected from it and what research says about your particular health condition.

The bottom line is, if you are fully vaccinated, you likely already have some level of protection. In reality, there’s no means to check your immunity or protection from COVID-19 at any time, including after vaccination. 

“The best measurement is having gotten vaccinated appropriately,” Campbell says.

The information in this article is current as of the date listed, which means newer information may be available when you read this. For the most recent updates on COVID-19, visit our coronavirus news page.