SARAH MCCAMMON, HOST:

We're going to start the program by addressing the devastating rise in COVID-19 cases across the country. The highly contagious delta variant has sent new U.S. cases surging to 100,000 a day on average. Those are numbers we haven't seen since winter earlier this year. And as public gathering places were starting to seem safe again, this latest surge in coronavirus cases is making a lot of us pause and think. Given COVID-19 will be with us for the long term, what will the new normal look like? So we've called Matt McCarthy. He's a physician, a professor of medicine at Cornell University and the author of "Superbugs: The Race To Stop An Epidemic."

Dr. McCarthy, nice to have you back on the program.

MATT MCCARTHY: Thank you for having me.

MCCAMMON: First of all, what is your reaction to what's been going on over the past few days? I mean, we're seeing an alarming rise in cases across the country, hospitals filling up again in many places. A lot of us thought, hoped that this was largely behind us. So what is your reaction?

MCCARTHY: It's a mix of pain and exhaustion. I'll tell you, the first thing that came to mind for me is - I used to be a relief pitcher. And I felt like I'd been in the bullpen and the game was going to be over. And it looks like I'm going to have to get back in. You know, it's becoming a regional phenomenon, where parts of the country are on fire right now. And you can just tell that other parts are - have it coming later in the year.

MCCAMMON: Of course, a lot of people still need to get vaccinated. But for those who are vaccinated, give us some perspective on these breakthrough infections that we're seeing, particularly with the delta variant. How much of a threat do those pose to fully vaccinated people and also to unvaccinated people?

MCCARTHY: Yeah. So the key message here is that these vaccines are holding up very well against the delta variant. We are seeing some breakthrough infections. Most of them are very mild. And as a practicing clinician, I'm simply not seeing healthy adults who are fully vaccinated showing up in the emergency room. People who end up getting sick are the unvaccinated and the people who have very weak immune systems who did get vaccinated. And that's a group that we're going to have to increasingly focus on. But for the rest of us, for the healthy adults walking around the United States, you can feel good that the vaccine that you received is going to hold up against the delta variant.

MCCAMMON: I mean, it seems like there's a challenge here for physicians and public health, you know, messengers, people like yourself who write and talk about science. On the one hand, the message is get vaccinated. Vaccines will keep you much, much, much safer than if you were not vaccinated. At the same time, we're talking about breakthrough infections. How difficult is it to explain to people, you know, that both of these things can be true at the same time?

MCCARTHY: Yeah. It is very challenging. And I appreciate the opportunity to try to do it here. What we have found back in December was that these vaccines prevent against serious disease and death. And then in May, the CDC came out and said, you know what? In addition to preventing serious disease and death, they also prevent transmission. And when that message came out, my reaction was, hmm, that seems a little premature. I'm not sure that we can go out and say that. And then what happened was in July, there was an outbreak of COVID in Provincetown. And what they found was that many of the people who got COVID had actually been fully vaccinated. And what happened was they found that the amount of virus in the noses of people who had been vaccinated and unvaccinated were essentially the same.

Now, that doesn't mean that they're equally contagious. This is a - you know, a complicated point to dissect. But what it's saying is that there's a lot of virus in the noses of fully vaccinated people. But what it doesn't say is if those people are actually spreading the virus around. And so if you are confused listening to this, I can tell you that public health experts are similarly confused sometimes when they're trying to figure out, how do we explain something to people that keeps changing?

MCCAMMON: What role do vaccines play in this larger question of how COVID mutates and spreads around? Will getting vaccinated and will wearing masks help keep more of these sort of scary, fast-spreading variants from being produced? Or are they going to evolve regardless of what we do?

MCCARTHY: No. The vaccines and the masks absolutely help. Every time the virus infects a new person, it has an opportunity to mutate. It has a chance to change into something that's more contagious and potentially more lethal. And when you can protect yourself, you're actually protecting the broader community. You know, many of the decisions that are made about lockdowns or about mask mandates have to do with the amount of cases that we're seeing on a daily or weekly basis. So when you put on that mask in a crowded supermarket, you are playing your part to keep this place that you live open, to keep it free.

You know, some people see liberty as something that's an individual choice and can only simply be about what their individual decision is. But, you know, this virus has revealed that we're all interconnected. And every decision you make is going to affect other people, even if you live alone. Your case matters.

MCCAMMON: If you don't mind my asking, whenever I talk to a public health official, I like to ask them this question. And you don't have to answer it if you don't want to. But what are you doing right now when it comes to protecting yourself, in terms of masking, in terms of social distancing? At this moment, given what you know about the delta variant and other variants, have you adjusted your behavior in the last few weeks?

MCCARTHY: I have. So I live in New York, where there has been very little COVID over the summer. So I felt very comfortable going to a crowded restaurant without a mask. I no longer feel that way. And the reason for that is that I have two young kids at home. I am not worried that I'm going to pick up the virus and become very, very sick. I'm concerned that I could pick up the virus and have very mild symptoms and inadvertently transmit it to one of my children. And so that's what led me to change my behavior.

MCCAMMON: The last thing I want to ask you, Dr. McCarthy - and it's not a directly scientific question, but it's based on your knowledge of the science. You know, we started this conversation by saying I think a lot of us had hoped we were mostly out of the woods here. And it's feeling like we're not. How would you advise people prepare themselves or think about this? I mean, is this the new normal? And what is the new normal going to look like?

MCCARTHY: Yeah. Well, I know people are tired and exhausted of having to think about this. This is going to be a seasonal virus in many parts of the country. I expect - the new normal for me is that I'm going to wear a mask during the months of January through March when I'm in a very crowded place. I expect that when I go to a grocery store five years from now, 20% of people will be wearing masks, not everyone. I expect these vaccines to hold up. I expect to be able to go to the movies and to do lots of things. But there are going to be certain months of the year where I am going to be a little bit more cautious. And again, that's because of my family life, but also because as a health care worker, I don't want to put myself at risk where I might not be able to go into the hospital and do my job.

MCCAMMON: That's Dr. Matt McCarthy, associate professor of medicine at Cornell University and the author of "Superbugs: The Race To Stop An Epidemic." Thank you for your time.

MCCARTHY: Thank you. Transcript provided by NPR, Copyright NPR.