As Americans look toward a return to normalcy after the coronavirus pandemic, a major question will be: Who is immune to the virus? To answer that question, the promise of antibody tests looms large.

These tests are different from the diagnostic tests used to determine whether a person is sick with the virus. Instead, the tests look for the antibodies in a person's blood that the immune system makes in response to an infection.

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Knowledge of who has antibodies could tell the estimated 25 percent of people who had asymptomatic infections that they did, in fact, catch the virus. And it would, in theory, answer the question of if and when anyone who has recovered from the illness could return to work safely.

The Centers for Disease Control and Prevention is among the institutions investigating antibody testing for COVID-19.

NBC News spoke to the head of the CDC, Dr. Robert Redfield, about antibody testing and immunity to the coronavirus.

The conversation has been edited for length and clarity.

NBC News: What will antibody testing actually reveal?

Redfield: From a public health perspective, it's going to let us understand the extent of infections that occurred in our country.

It will give us a much more accurate understanding of the symptomatic vs. asymptomatic ratio, and will give us a much better understanding of the mortality, once we see the full extent. Also, it can be useful in defining high-risk populations that are conceptually immune.

I think it's important to emphasize that we haven't yet proven that once you develop antibodies, [you develop protective immunity]. It's still a scientific hypothesis that this virus will lead to protective immunity of some duration.

A lot of that won't really be validated until we begin to see the next fall, winter, [when] we'll have a large group of individuals predefined that has been serologically positive [for antibodies] that are in high-risk professions — health care professionals, high-risk situation institutions like nursing homes.

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Then we'll be better able to understand what I think most of us hypothesize will be true, that, like other coronaviruses like SARS and MERS, there will be a protective immune response that will have a durability to it.

So, in certain critical infrastructure groups, that may help accelerate some of these groups reopening [and] would give great confidence for some of the public to return to work.

NBC News: Is there anything to antibody testing on an individual level? For those who want to go get that test to know if they can go back to work, is there any benefit to the individual? Or is antibody testing just a broad public health benefit?

Redfield: In certain circumstances it can have a benefit to the individual, for example, health care workers. It may help hospitals, if they look at the next wave, which I believe we will have in late fall or winter, they may be able to identify a group of health care professionals that are no longer likely to be susceptible. That may have impact on how the health care system can take care of coronavirus-specific individuals.

I suspect hospitals will begin to look at having coronavirus-specific areas, if not hospitals, for next year. And coronavirus-specific nursing homes. It would obviously be useful in nursing homes to have health care professionals who are immune.

I think there is this assumption that it may accelerate confidence in some individuals in returning [to work] as though I'm immune, but I really think its major role is going to be in more of a public health role and the impact that it has, as we try to develop some alternative care delivery mechanisms to be available for fall and winter, when in fact we will probably have additional coronavirus infections.

The hope is that we won't have to go to such dramatic mitigation strategies as basically shutting down schools and the economy because we would have a strong public health workforce. We have created the capacity within the public health system to effectively operationalize containment as we go through the second wave.

NBC News: Do we know anything about how long a person might have that immunity?

Redfield: There's a hypothesis that there is going to be protective immunity. We think there is protective immunity because we have examples in animal models to support that. We're going to be getting real-life information, as we move through the next 12 months to be able to reaffirm that. But to answer your question about duration, I think the only way we're going to know that is with time.

I don't think we have any real life, human data on what is the durability of protection.

NBC News: What's your prediction for when might we expect accurate large-scale antibody testing?

Redfield: I think the serology surveys are going to give us a better understanding of the differential disease penetration that occurred in different populations. For example, in younger individuals versus older individuals and individuals with pre-existing conditions, those without them. We'll have all of that crystallized, I think pretty well, over the next several months.

Is the immune response protective or not? I think that's going to take us, pretty much, through the next year to be able to understand what the protection is.

But that still won't answer the key question you asked me: Is the immune response protective or not? I think that's going to take us, pretty much, through the next year to be able to understand what the protection is, and how long we can see that last will probably take years for that to happen.

The first serology tests have already been approved by the FDA. There's a number of other tests that are available, that are being validated. I think we'll see more large company serology tests be available in the weeks ahead.

Then it will just depend on what is really the strategic way that this test should be used. I think you will see it used in certain circumstances to help certain companies make decisions about back to work, particularly in the critical infrastructure. We really want to have a critical workforce that is going to be potentially immune to this same situation that is very likely. The virus is very likely to come back very significantly in the next coronavirus season, which will happen next December, January, February.

I think that we will be much more prepared for it as it comes back a second time.

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NBC News: So would the antibody tests be reserved for people like our health care workers who might need it most?

Redfield: I think the availability of the test for antibodies will become quite available.

There will be employers that will want to have some knowledge, as they plan for 2021. It's definitely going to be aggressively employed in public health so we can do public health planning.

But I do think it will be available for individual doctors and individual people to make a judgment about whether they want to know their antibody status.

NBC News: What do you say to those people who, despite never having been tested for coronavirus, are insisting they probably did have it within the past few months, and are now assuming they're immune?

Redfield: I would beg them to stay with this. Behavioral modification is something that, when it's for our health, we're not that good. But what I've learned about from this outbreak is when my behavior modification helps your health, or saves your life, the American public has done a great job. So I would first really beg people to stay with this. We need to really maximize our social distancing. It's all hands on deck right now. No letup.

I want everyone to stay firm — all hands on deck until we're comfortable the transmission of this virus has not slowed, but stopped.

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