Researchers are racing to develop tests that detect whether someone may have developed immunity to the coronavirus, which could help society return to normal faster.Why it matters: These tests could help people know if they are able to go back to work, as well as aid researchers in tracking the scale and death rate of the disease — key data for current and future pandemic policies.Background: SARS-CoV-2, the virus that causes COVID-19, is new to the human body, meaning there's no innate immunity. And, since there isn't a vaccine — and there won't be for a while — it's difficult to ensure someone will be protected from the virus unless they know they've had the infection.But people without symptoms can have COVID-19 and not know it, making it more difficult to pinpoint who's had been infected.How it works:  When the body is exposed to a virus, the immune system begins to produce antibodies to fight the virus and future infections from it.Those antibodies stick around after the virus is cleared from the body, making them an indicator of past infection.Serological tests check the blood for these antibodies — providing confirmation of infection and possible protection.That’s different from the diagnostic tests receiving most of the public's attention; those confirm whether someone has an active infection.These tests could be especially useful for determining whether health care workers have some immunity and are at lower risk if they go back to work, says Nick Evans, an assistant professor at UMass Lowell.They can also be used to sample the population in order to form better estimates of the scale of infection and the death rate of the virus, says Jesse Bloom, a virologist at Fred Hutchinson Cancer Research Center.Where it stands: Researchers at universities, companies and the Centers for Disease Control and Prevention are working to develop tests to detect antibodies to SARS-CoV-2.Academic labs can develop the tests relatively quickly but to carry them out on a clinical scale with a large number of samples is "in some ways as much a matter of logistics as science," says Bloom, who's also an investigator with Howard Hughes Medical Institute.British officials said Wednesday they were ordering at least 3.5 million "finger-prick" serological tests that could be purchased via online entities like Amazon and taken at home, per Nature. The catch: The utility of the test hinges on the supposition that people who've had COVID-19 are immune to new infections — an open question as "the evidence is not ironclad," Bloom tells Axios. But preliminary research suggests that, unlike influenza viruses, SARS-CoV-2 isn't mutating fast and infection with the virus could confer immunity for months to years.And in a small study that has not been peer-reviewed, researchers were unable to reinfect macaque monkeys that had been previously infected with the virus.What to watch: Widespread testing could raise privacy concerns. "People still have privacy rights, even in a pandemic, and I don't see a reason for public disclosure. That's important, because my hunch is people's worst natures will show up and they'll start demanding disclosure, much like with other infectious diseases (e.g. HIV)," Evans said.Go deeper: How does the coronavirus behave inside a patient? (The New Yorker)