Anthony Fauci, 79, is the director of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health. He has advised six presidents on health epidemics. The Washington Post Magazine interviewed him by phone on March 20.

How are you balancing trying to explain this pandemic to the public, so they really understand what’s going on, without creating hysteria?

The fact that you're asking that question — I think you realize that it's a delicate balancing act. And it's hard to do because you have to be truthful. You don't want to withhold important information. At the same time, it's frightening for people, understandably so. So here's what you do: You make sure that you always tell the absolute truth and don't hold back data. For example, the one thing that I have been saying that never came across particularly clearly in the way some people — and I'm not mentioning names — have expressed this: We are in the escalating phase of a very serious pandemic. That is a fact. We have got to realize that and to prepare and respond. It is not, as it were, under control. Because it's still going up. Are we trying to control it? Yes. Are we having an impact? We are doing some rather dramatic things. California shutting down. New York doing the same thing. And for the country in general, the physical separation. So even though the inflection is going up, there's no doubt that what we are doing is having an impact.

When you look at what happened in China and in Italy, you can't run away from the potential of what this virus can do. That's the reason why, when people ask me how long is this going to go on, we don't know. If you look at the pattern, things are not going to turn around in two weeks. I mean, it's just not going to happen. We're in a several-week, I guess, fight, if you want to call it that. At best.

You’re talking to the public directly, and you’re also speaking with the administration — you said you’re heading into the White House now. Do you have different messages for different people, or different ways of sharing the message?

No, no. I give my message loud and clear in there. I tell it like it is. Inside and to reporters like you.

And do you feel the White House is getting the message? Or not?

I think they are, to be honest with you. Sometimes it doesn't appear that way when public announcements come out and how it's expressed. But behind closed doors, they're getting the message. They really are.

The AIDS epidemic was the first major epidemic that you dealt with personally, and you developed a good working relationship then with [AIDS activist] Larry Kramer, which I think was unusual. What did that experience teach you about how to respond today?

There were multiple, multiple lessons from HIV. But one of them was you've got to get the community involved. You've got to be honest and open. You can't have a separation between the people who are in authority trying to do something and the people who are out there experiencing this and anxious about it.

Do you think that’s something that’s understood now — or heeded?

I think it is, I think it is. You got to remember that, KK, this is a really unprecedented situation. I've been involved in every major outbreak since the 1980s, when I was working with Ronald Reagan as the president. And this is unusual. You're seeing it play out in other countries — in China and in Europe — and seeing what it potentially can do. Seeing the escalation of cases here, of course, is frightening to the American public. That's why they've got to get used to the fact that we are dealing with a serious situation. We cannot sugarcoat it. We've got to do everything we possibly can to counter it. To mitigate it. Everything. To me, it's like we're entering into a world war. It's almost like, Okay, they've just bombed Pearl Harbor, and they've invaded France. Uh, hello. What are we going to do here?

So when you see images of people out jogging or hanging out, what does that make you feel?

I'm actually pleading with the younger generation that, although you feel you are invulnerable — which is not true; nobody's invulnerable — the fight is not only trying to protect yourself. You have a societal, in some respects, moral responsibility to protect yourself so that you don't then inadvertently and unintentionally infect those who are more vulnerable. So people in bars and in restaurants and on the streets hugging each other, in crowds, it just completely frustrates me to see that.

You’ve been in public health for your whole career. From a policy point of view, have we taken our eyes off the ball so that we’re not as prepared as we should be?

No. And this is something that often gets expressed incorrectly and misquoted. Not that I'm saying you're going to do it. The fact is, no matter how well-prepared you are, if you have a really full-blown pandemic, it will always appear — and maybe be reality — that in fact you're not as well-prepared as you should be.

So what do we need to learn from it?

We need to learn that we need to do as best as we possibly can. And it'll always appear that we're not well-prepared. But let's put that behind us. Right now, we've got to marshal all our resources. Pull all the stops out. That's what we got to do right now.

What’s the best-case scenario, in your mind, for how this plays out?

The best-case scenario is that our mitigation efforts blunt that curve so that the peak you keep seeing me showing on television becomes muted to the extent possible. That would be the best-case scenario: Our mitigation is successful. But our mitigation is not going to protect us from any kind of harm or death. Bad stuff is going to happen. We got to make sure it isn't really bad.

This interview has been edited and condensed. KK Ottesen’s latest book is “Activist: Portraits of Courage.”