And public health experts are warning that just because a person has antibodies to the coronavirus doesnt mean they are immune to it.

Heres what you need to know about antibody testing including why its unlikely well be able to crowd into a bar or a baseball stadium anytime soon.

1. How do the tests work, and what can they tell us?

Antibody tests, also known as serological tests, analyze a persons blood for evidence that they have been infected with the coronavirus even after they have recovered.

That data can help public health experts better understand how many people have been infected and adjust their models of the U.S. outbreak, said Kelly Wroblewski, the Association of Public Health Laboratories director of infectious diseases.

Widespread antibody testing could also help inform decision making about when to start reopening parts of the economy, but scientists arent sure if surviving a coronavirus infection confers immunity, how strong that immunity might be and how long it could last.

Just because you have antibodies doesnt mean you have immunity, Carlos del Rio, executive associate dean of the Emory School of Medicine, told reporters Friday.

Wroblewski said that while its reasonable to assume survivors gain some level of immunity, it is important to proceed with caution. “Everybody is being optimistic you have some sort of sustained immunity for at least the ensuing months to a year, she said. But it is still somewhat an assumption.

2. Whats the government doing to ensure the tests are accurate?

The FDA said in March that it would allow companies to develop and distribute validated antibody tests without review under certain circumstances including that test-makers notify the agency and include disclaimers in test results.

More than 90 tests are now on the market, and most have bypassed FDA review. Diagnostic manufacturers, public health labs and commercial labs have raised concerns about the accuracy of these tests. They want the FDA to take a tougher regulatory approach to ensure the quality of antibody tests.

Top government officials, including HHS testing “czar” Brett Giroir and Hahn, have said the public should only rely on antibody tests reviewed by the FDA. But the agency has given emergency authorization to only one such test, manufactured by Cellex.

There should be a strong evaluation process that goes on ahead of getting these tests out there, APHL CEO Scott Becker told POLITICO.

The National Institutes of Health, Centers for Disease Control and Prevention and the FDA are each working to assess the accuracy of antibody tests that havent yet undergone FDA review.

“There has been some concern about the accuracy of at least some of these tests, so the FDA in collaboration with other agencies is standing up a voluntary program to help address and verify their accuracy, FDA diagnostics chief Tim Stenzel said on a webinar last week.

3. Will widespread antibody testing be available soon?

The Trump administration said over the weekend that it would require most private insurers to cover coronavirus antibody testing at no cost to consumers. But so far, very few Americans have undergone such testing.

Giroir and other members of the administration have predicted that tens of millions of antibody tests will soon be under production, but it is unclear how soon they will reach the public.

I think were still weeks away from the logistical aspects of this kind of mass testing program, Becker said. We in public health are looking for a high-quality test that can be used for serology studies to understand the dynamics of immunity within each community.

Once the logistics of administering tests are resolved, frontline health care workers should have priority, said former acting CMS Administrator Andy Slavitt. That can help workers who suspect theyve been exposed to the virus return to work if they have antibodies.

It will be important in the future and at least important for health care workers in New York and other places, Slavitt told POLITICO. But until more is understood about potential immunity gained after being exposed to the virus, he added, antibody tests are unlikely to be a game changer.”

4. Could the tests help the U.S. ease social distancing measures?

Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases, last week raised the possibility of issuing immunity certificates to people who test positive for coronavirus antibodies.

But antibody tests cannot be the sole mechanism for deciding who can return to work, according to Gigi Gronvall, an associate professor of immunology at the Johns Hopkins Center for Health Security. Doing so may induce perverse incentives for people to lie about their antibody status or purposefully try to become infected.

If youre going to develop a system like that, you need to make sure its legally okay, Gronvall told POLITICO. You can imagine there would be some HIPAA challenges and also employment discrimination challenges.

Another worry is that the use of antibody tests to reopen parts of the economy may give the public a false sense of security. Allowing some people to return to work could cause others to become less diligent with social distancing measures before its safe to do so.

The federal government should probably right away say how [the tests] ought to be used, or at least how they should not be used, Gronvall said. Businesses will certainly start using them, and I worry about the consequences for public health if people decide that their employment rests upon getting this disease.