The race is on to develop and distribute antibody tests for the coronavirus, driven by the idea that these tests will inform individuals when they are immune to the virus and can return to their normal lives.

This isn’t the first time there’s been an urgent need for an antibody test. In the 1980s, it was a different crisis: HIV/AIDS. Unlike the coronavirus, a positive antibody test for HIV means that a person is currently infected with the virus, meaning the test could be used to diagnose.

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Dr. Robert Gallo, the co-founder and director of the Institute of Human Virology at the University of Maryland School of Medicine, was one of the scientists who discovered HIV, and later went on to develop the first antibody test for the virus.

NBC News spoke to Gallo about antibody testing, and what it can tell us about the coronavirus. This interview has been edited for length and clarity.

NBC News: What do you think the need is right now for an antibody test?

Gallo: The No. 1 reason for me is to know the extent of the epidemic. You're able to follow the spread of the virus to know the reality of what is going on.

Some people will say the tests can do more. They'll say, 'well, the antibody test also means you can go back to work.' That may be true, but we can’t tell if the antibodies are protective. There are some suggestions that when you have antibodies, you're associated with clearing the virus when the antibody titers are good. [A titer is a measurement of antibody levels in a person's blood.]

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But that's not always the case. Sometimes the antibodies are positive and the person is still very infectious. So, you have to remember that.

I'd like to say there are antibodies and there are antibodies and there are antibodies. Some are nothing at all. Some are protective indicators. And sometimes, though not so commonly, they can make matters worse.

For example, dengue fever — if you get infected and have antibodies and then get infected again, you do worse. Another one is in babies, the respiratory syncytial virus. They can have antibodies that make things worse.

With antibody testing, though, we need it — very much for knowing the context of the epidemic and to be able to predict the future to know whether the antibodies are correlating with doing anything. It's vital. Some people have said in press conferences that it wasn't the highest priority. It is the highest priority. There's nothing of higher priority.

NBC News: There are dozens and dozens of antibody tests in development from a variety of different places, and they all seem to be a little bit different. What do you think an antibody test needs to have? What exactly does it need to measure in order for it to be useful?

Gallo: Well, you want accuracy, you want specificity, you want sensitivity. You don't want to increase sensitivity and sacrifice specificity, which is a problem with this virus. We don't know all the problems yet, but we're seeing problems.

One thing that we know for sure is a problem is the other mild coronaviruses that infect us. In addition to SARS and MERS, which cause severe illness, there are three or four other coronaviruses that will give you cold-like symptoms. Some of these milder viruses are widespread, so you may have antibodies to them. The question is, do antibody tests for this coronavirus pick up antibodies for other coronaviruses? It looks like with many of the assays, there are some cross reactions. So that's a problem because we're gonna get false positives.

Of course, we can conquer that. That's what the academic research labs are doing and maybe some of the companies, as well. It's a research problem.

Ultimately, what you’re looking for in this virus — compared to any other coronavirus — is a protein or proteins that are distinct or different enough, that there won't be cross reactions, with other coronaviruses.

NBC News: How confident are we that if we do have these antibodies and we're identifying the correct ones, that we've now become immune, that we can't get sick again?

Gallo: We've been hearing that at those press conferences, but I don't agree with it. I think that you have no idea that you're going to be protected, because you don’t have the data. There are variations. Take HIV for example — if you have certain antibodies and a lot of antibodies against HIV, you're not protected.

It takes more than that. It takes very, very specific kinds of antibodies at a high enough titer, etc.

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On the other hand, a positive antibody could mean you're protected. But it could mean what I mentioned with dengue. I don't think it is. But imagine what it would mean that you'd be worse off.

So you understand that you're hearing statements that are simplistic a lot of times. I don't understand why they just can't say, it's likely that will be true, but we cannot say that with any absolute certainty.

Why do we want the test? For the reasons I said. Does it tell you for sure, go back to work? No, but it's a guide. It helps. And it's certainly necessary for understanding the epidemic, and where it's going.

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