Is There a Way to Know If You’ve Never Had COVID?

Roughly 57% of people in the United States have never gotten infected with COVID-19, according to the estimates from a Centers for Disease Control and Prevention (CDC) seroprevalence (testing for antibodies in blood) survey. Researchers are now taking a closer look at the “never COVID” cohort as well, or people who may be immune due to past infection, vaccines, or a combination of both.

While it may be tempting to think or assume everyone has gotten COVID at least once based on the widespread nature of the virus, it’s not a conclusion that can be reached at this time, Samantha Wu, MD, MSPH, medical director of clinical development at Goodpath, told Verywell in an email.

“Our understanding of someone’s lifetime risk of getting COVID will evolve alongside many different factors, including the presence of new variants, as well as advances in our surveillance and vaccination efforts,” Wu said.

But if you find yourself being a part of the “never COVID” group at this stage in the pandemic, is there a realistic way to prove that? In other words, how can you know for certain if you’ve never had COVID-19, especially in cases of people who never develop or show any symptoms?

Is There a Realistic Way to Know If You’ve Ever Had COVID-19? 

Currently, health experts say there is no reliable way to know for certain if you’ve had COVID-19 in the past two years, particularly if you were never diagnosed with the virus from either a test or a healthcare provider.

“This is a challenge because asymptomatic COVID infections can occur, so the absence of acute COVID symptoms does not always correspond to the absence of infection,” Wu said.

There are some methods including antibody tests, also known as serology tests, that can confirm a past COVID-19 infection, and in certain cases, help pinpoint the timing of when a COVID-19 infection occurred, Fady Youssef, MD, a board-certified pulmonologist and critical care specialist at MemorialCare Long Beach Medical Center in California, told Verywell.

Youssef explained when the body is exposed to an infection it forms several classes of antibodies (proteins that can protect against future exposures to viruses). Antibody testing can detect those levels of antibodies and signal if the body is currently infected or if an old infection occurred.

However, the timing of when you take an antibody test is important because over time some antibodies will start disappearing and may become undetectable. Youssef said the longer a person lives without the infection, the more likely their immune system will return to its baseline.

He added that you have the highest likelihood of detecting antibodies if you test within three to four weeks from the onset of symptoms. If you do the test earlier, the body may not be able to detect those antibodies reliably. For an asymptomatic person, that may be impossible.

“If you do it after that window, then the antibody response starts to wane and the results will not be accurate,” Youssef said. “Serological testing or antibody testing is not as reliable as one would hope and the Infectious Diseases Society of America (IDSA) has a recommendation that serological testing should not be used to determine immune status.”

According to Wu, exactly how long antibodies last after infection is still under evaluation, but studies have shown detectable levels of antibodies in COVID-19 patients at 8 months and up to one year after infection. Data also suggest that those with more severe initial infections generate a stronger antibody response that persists for a longer period of time. 

Although antibody testing may be useful for an individual to confirm prior COVID-19 infection or be used to support the diagnosis of long COVID, it may not be the most reliable or accurate way based on how long antibodies last in the body.

Can You Differentiate Between Vaccine and Infection-induced Antibodies?

Experts say serology tests can differentiate a past COVID-19 infection from vaccination, which means certain tests can detect antibodies that form after infection versus antibodies that are made from a vaccine.

According to Wu, this is possible because COVID vaccines produce a specific type of antibody response. There are also different types of available antibody tests.

“If you look at antibodies against viral antigens like the nucleocapsid (N) protein, the vaccines that are used in the United States do not elicit such antibodies,” Youssef said. “If you have a positive result on a nucleocapsid protein-based serology test and you are an individual who had a vaccine, then that would suggest that there was a prior infection.”  

If a person who was never vaccinated tests positive for antibodies against specific viral antigens such as nucleocapsid (N), spike (S), or receptor-binding domain (RBD), then that would indicate a prior infection.

However, in vaccinated people, if they test positive for antibodies against the vaccine antigen target, such as the spike (S) protein, and negative for other antigens like N and RBD, then it would suggest they have produced vaccine-induced antibodies and were never infected with COVID-19.

If you also test positive for antibodies other than the vaccine-induced antibody, such as the N protein, then that indicates a past COVID infection could have occurred before or after vaccination.

Are Antibody Tests Recommended? 

Antibody tests can be useful for surveillance purposes and can help scientists understand patterns of COVID-19 infections in the setting of vaccination, Wu said.

However, it is not recommended to:

• Determine a person’s immunity following vaccination
• Inform whether an unvaccinated person should be vaccinated
• Diagnose an active infection
• Determine the effectiveness/responsiveness against a different variant

Youssef added antibody tests could be useful for some people who are showing COVID-like symptoms but are receiving multiple negative COVID-19 test results.

“While serology testing may seem to offer at face value peace of mind if you look into the details, it does not offer clear-cut answers in most situations,” Youssef said. “There are a lot of caveats to serology testing results. If somebody has gone through the past couple of years, they never got diagnosed with COVID and they feel fine, then serological testing is unlikely to be of value to them.”