(NEXSTAR) — Sore throat, runny nose and a headache — the symptoms could mean your body is fighting through a cold, the flu or a COVID infection. You might not have had access to a COVID-19 test, or maybe your symptoms went away before you had the chance. There’s also the possibility you tested too early in the infection, so you got a false negative.
Is there a way to tell if that sickness you had a month ago, or even last year, was COVID or something else?
The short answer is yes. In practice, however, the answer is more complicated.
The way to tell whether or not you had COVID-19 in the past is by using antibody, or serology, testing. When your body is exposed to the virus, it creates antibodies to fight it off. These tests look for those antibodies to confirm past infection.
Your body also creates antibodies when you get the COVID-19 vaccine, but these tests can actually tell the difference between the two types of antibodies.
There are two types of antibodies your body produces: antibodies against the spike protein (S), which are created by vaccination, and antibodies against the nucleocapsid (N), which are created by prior infection.
If a test finds you have the N-type antibodies, it indicates prior infection, a Centers for Disease Control spokesperson explained to Nexstar. If the test finds you have S-type antibodies and don’t have N-type antibodies, then it indicates you’ve been vaccinated but haven’t been infected.
It can take weeks for someone to develop antibodies after infection, the CDC said. If you think you’ve been exposed to the virus recently, you should seek out a viral test, like an antigen or PCR test, instead.
Someone can test positive for antibodies even if they never had COVID symptoms.
Both the CDC and the Food and Drug Administration have said they do not recommend antibody testing as a way to determine if you’re protected from the virus.
“CDC is evaluating antibody protection and how long protection from antibodies might last,” the agency says. “Cases of reinfection and infection after vaccination have been reported, but remain rare. But getting vaccinated, even if you have already had COVID-19, can help your body make more of these antibodies.”
Antibody tests cannot distinguish between COVID-19 variants, the CDC said, so they can’t be used to tell which variant a person was infected with.
If you’d like to get antibody testing done, the CDC suggests contacting your local health department or your doctor’s office for a referral to a lab.