By now, youve probably heard about the coronavirus antibody tests, and how they may be the best shot weve got at opening up the economy and returning to some sort of normalcy.

Researchers and hospital systems across the country have started conducting antibody tests on thousands of people to map out just how far the novel coronavirus spread over the past few months. Initial antibody test results out of California suggest that up to 4% of residents in hard-hit counties may have already had COVID-19, whether or not they realized it.

Though the tests are giving us a stunning snapshot of just how many people may have already been infected, too many unknowns still surround COVID-19 mainly the are recovered people immune? question to say that antibody tests are our ticket out. But, used in conjunction with other testing and tracking efforts, they could very well help us get control of the pandemic.

Heres how the antibody tests work, and what they mean for our health.

First, what is an antibody?

When a virus gets into the body, it attaches to a cell and begins to replicate itself.

At the same time, our cells realize that somethings not right and send out distress signals. Those distress signals zip through the body and jump-start the immune system, our bodys defense system against any harmful germ, virus or bacteria.

They say, Virus here! and the immune system gets those messages and shows up and starts trying to figure out what virus it is, said Sheldon Campbell , associate director of Yale Medicines Clinical Microbiology Lab and associate professor of laboratory medicine at the university.

Then, depending on the virus and how dangerous it is, the immune system mounts a response that involves a whole bunch of different cells banding together to wipe out the invader. One of the systems tools in its fight are antibodies, these large Y-shaped proteins that fuse with a part of the virus called the antigen, and disarm it, Campbell said.

Typically, the antibodies along with all the other ammo the immune system has in its arsenal control the infection and protect us from harms way.

And those antibodies dont just do their job and disappear. They linger in the body, for varying amounts of time depending on the illness, so that if the virus strikes again, the body can act fast and knock it out. (For reference, SARS antibodies were maintained for about two years after infection, MERS antibodies seem to last at least 34 months. We still dont know how long COVID-19 antibodies hang around.)

The tests examine a blood sample for COVID-19 antibodies

Antibody tests start with a physician drawing blood for a test, sometimes with just a finger prick. The blood is then taken to a lab, where the serum and plasma are isolated from the sample. The patients plasma is then exposed to a part of the coronavirus (the antigen) to see if the antibodies remember the virus. If antibodies to the coronavirus are present thanks to a past infection, theyll stick and bind to the virus.

What it tells you is if the person has been exposed to the virus and had an immune response to the virus, said James Zehnder , director of clinical pathology at the Stanford University School of Medicine.

Its worth noting that antibody tests are not the same as diagnostic tests, like the nasal and throat swabs. Antibodies tell us a person has been infected after the fact , not during.

It takes antibodies a couple of weeks to develop after being exposed to a virus, according to Akiko Iwasaki , a professor of immunobiology at Yales School of Medicine. Therefore, an antibody test should not be conducted on a person until theyve been recovered for at least two weeks.