officially known as COVID-19. The virus has now killed more than 2,000 people worldwide.

William Brangham has the latest.

WILLIAM BRANGHAM: There are still many, many questions researchers have about this viral

outbreak. but we do have new information from the Chinese government about the virus' mortality

rate, and other important concerns.

Dr. Anthony Fauci is the director of the National Institute for Allergy and Infectious diseases

at the NIH. He joins me again tonight from the NIH campus.

Dr. Fauci, thank you very much for being here.

Chinese officials seem increasingly confident that they're able to get their hands around

this outbreak. They think they're going to contain it and seemingly arguing that the

number of new cases is going to plateau pretty soon.

Do you agree with that?

DR. ANTHONY FAUCI, Director, National Institute of Allergy and Infectious Diseases: Well,

I think we really, really need to wait and see if that's the case.

They have been talking about the numbers of cases each day being less than the previous

day over the past few days in a row. I would hope that that's the turning point. But I

really think we need to reserve judgment on that, because we still have a very serious

problem in China right now.

So, hopefully, that's making the turning around. But I'm not quite sure of that yet.

WILLIAM BRANGHAM: I mentioned before about how we're getting a better look at the mortality

rate of this virus, meaning, of the number of people who get infected, how many are likely

to die?

What can you tell us about that?

DR. ANTHONY FAUCI: Well, if you look at the official counts of the 70-plus-thousand people

infected and the about 2,000 deaths, the mortality -- or the case fatality rate, as we refer

to it, is approximately 2 to 2.3 percent.

If you compare that with seasonal influenza, which is 0.1 percent, this is a serious level

of mortality, not as bad as SARS back in 2002, which was 9 to 10 percent, and the Middle

East Respiratory Syndrome, another coronavirus in 2012, which was about 36 percent.

I do not believe that the 2 percent is the really ultimately correct case fatality rate.

And the reason I say that is because the denominator for that calculation is probably much larger

than they are putting into it.

For example, there are many, many individuals who have either asymptomatic disease or minimally

symptomatic, which means they're not being counted as an individual who is sick. So,

when the denominator gets much larger, then the case fatality rate will go down.

So, myself and other of my colleagues are figuring that it is likely 1 percent or less,

when you count all the people who are infected and do the calculation for a fatality rate.

WILLIAM BRANGHAM: We also know that this is a fairly contagious virus. But there has been

some question as to whether or not people are contagious before they show symptoms.

What do we know about that?

DR. ANTHONY FAUCI: Well, we certainly know that there are a lot of people who are infected

without symptoms.

There have been anecdotal cases that I think are pretty solid that there has been transmission

from a person who has no symptoms to another person. I think that's going to turn out to

be a real phenomenon.

The question that still remains unanswered is, what is the extent of that asymptomatic

transmission? Is it a minor component of the outbreak or it is a substantial component?

If it is a substantial component, that then becomes problematic, because that would mean

that, when you do screening for people, you can't rely just on whether or not they're

symptomatic. You have to do a test. So that's the big question that we're pursuing right

now.

What is the degree of asymptomatic transmission?

WILLIAM BRANGHAM: On this issue of contagiousness, there's a term that people might have heard

floating around, this issue of a super spreader, someone who's particularly contagious.

Is that a real phenomenon?

DR. ANTHONY FAUCI: It is a real phenomenon.

We saw it very clearly in the SARS outbreak in 2002. And there are a number of episodes

now that have been reported that indicate that a given individual -- I mean, the word

super spreader is used, and that kind of confuses people what you mean by that.

It means that a person has such a high level of virus that they're shedding that, when

they come into contact with a group of people, that the odds of their infecting more than

just one of them, maybe several people at a shot, those are the ones that we're calling

super spreaders.

We have seen it within family units, and we have seen it particularly among health care

providers, where you have one person might infect five, six, seven or even 10 health

care providers, hence the designation of a super spreader.

So the answer to your question is that it is a real phenomenon.

WILLIAM BRANGHAM: All right, Dr. Anthony Fauci, thank you very much for the update.

DR. ANTHONY FAUCI: Good to be with you.