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Web Extra: Dr. Anthony Fauci On The 'Mystical Terminology Of Herd Immunity'

WASHINGTON, DC - APRIL 15: Dr. Anthony Fauci, Director of NIAID and Chief Medical Advisor to the President, testifies at a House Select Subcommittee on the Coronavirus Crisis hearing on April 15, 2021 on Capitol Hill in Washington, DC. The committee is hearing testimony on "The role of the National Institute of Allergy and Infectious Diseases in Research Addressing COVID-19." (Amr Alfiky-Pool/Getty Images)
WASHINGTON, DC - APRIL 15: Dr. Anthony Fauci, Director of NIAID and Chief Medical Advisor to the President, testifies at a House Select Subcommittee on the Coronavirus Crisis hearing on April 15, 2021 on Capitol Hill in Washington, DC. The committee is hearing testimony on "The role of the National Institute of Allergy and Infectious Diseases in Research Addressing COVID-19." (Amr Alfiky-Pool/Getty Images)

The United States is at a new inflection point in the COVID-19 pandemic. Public health experts are beginning to say that the country may not reach so-called “vaccine-mediated herd immunity.”

“I always say there’s this elusive, somewhat mystical terminology of ‘herd immunity’ and ‘herd immunity threshold,’ ” Dr. Anthony Fauci says. “You know, that is when you get such a blanketed protection over the community. And we don’t know what that number is. I mean, it’s an estimate. I have estimated for months now it’s somewhere between 70 and 85 percent.”

While Fauci says he’s always called herd immunity somewhat elusive, it’s only very recently that he, and other public health leaders, have ventured to say clearly we may never reach that threshold — no matter what it is.

And why? About a third of American adults are fully vaccinated. More than half have had at least one shot. But new daily vaccinations are dropping, and polls find that about 30 percent of the US population is still reluctant to be vaccinated.

That’s leading some public health experts, including former FDA commissioner Scott Gottlieb, to say that they don’t expect much more than 50 percent of Americans to eventually be fully vaccinated.

In this special web exclusive, Dr. Anthony Fauci joins Meghna Chakrabarti to discuss herd immunity, potential measures to help guide public health decisions and more.


In this web exclusive … we hear from:

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. (@NIAIDNews)


Full Transcript:

Anthony Fauci: Well, [the vaccination efforts] continue to do really, really very well. If you look at the fact that we now have over 200 million doses, about 220 million doses were given during the first 100 days of the Biden administration. So, things continue to look good. We’ve had a slight dip. We were averaging between 3 and 4 million doses a day. We’re now at about 2.9. So that’s close to 3 million per day. It’s expected as the cohort of people that you’re vaccinating becomes less and less because you vaccinated more and more, that the number of vaccinations per day are going to diminish a bit. But we’re going to continue to really push and reach out to people to get trusted messengers, to convince people, people who they trust as to why it’s important for your own health, the health of your family and that of the community to get vaccinated. So bottom line is the vaccine rollout program is going really very, very well.

Meghna Chakrabarti: You know, it is very reasonable, as you said, that in this phase of a mass vaccination campaign that the daily rate might slow down. But what I’m really interested in our overall goals. Right? Because historically — and when I say that, I mean, over the past several months — I’ve heard you say repeatedly that in order to achieve that so-called a vaccine-mediated herd immunity in this country, we’re going to be needing to aim to around the 80 percent mark, if not higher, of adults being fully vaccinated. At this point in time, Do you still think we can reach that number?

Fauci: Yeah. You know, Meghna, I want to clarify one thing so that people don’t get confused. And I always say there’s this elusive, somewhat mystical terminology of “herd immunity” and “herd immunity threshold.” You know, that is when you get such a blanketed protection over the community. And we don’t know what that number is, Meghna. I mean, it’s an estimate. I have estimated for months now it’s somewhere between 70 and 85 percent. But we really don’t know that because that’s influenced by so many factors: the durability of immunity for people who’ve previously been infected, the appearance of variance and things like that. So I prefer rather than concentrating on this somewhat nondescript concept that we still don’t know what that number is, is to say, “Let’s get as many people vaccinated as quickly as you possibly can.”

And even if you don’t reach whatever percentage that number is going to be, you’re still going to have a profound impact on the number of infections in society. So people sometimes think that you’re not going to have a real dramatic drop in daily infections until you reach this very elusive terminology of vaccine immunity or herd immunity threshold. You can start to see really important results as you get closer and closer to it. So every day that goes by that you get an additional 3 million people vaccinated, you’re going to start seeing getting closer and closer to start seeing a significant diminution in the number of cases.

For example, for several, several weeks, we had a seven-day average of about 60,000 infections per day. It is gone down now over 20 percent or more, down to somewhere in the 50,000 per day. And as we get more and more people vaccinated, it’s going to go down to 40 and then 30 and then 20. So we don’t know what this number is of what percent people vaccinated is going to be. But we do know something for sure, Meghna. And that is: the more people you get vaccinated, the closer and closer you get to getting control in the community, which is the reason why we so strongly recommend and plead with people to get vaccinated, not only for their own protection, but for that of their family and for the community.

Chakrabarti: I’m really intrigued by what you’re saying. And on this show, what we’ve been trying to do for the past year is kind of help people navigate the uncertainty that COVID has thrust us all into. And what I found is that people want tools on how to decide how to live, what to do, what’s safe, what’s not safe. And one of the tools that’s helpful is to kind of have a goal to aim for, which is why people wonder about what threshold do we need to reach for herd immunity. And it’s interesting to hear you say that maybe that number isn’t so important anymore. That’s coming at a time where I’m hearing other public health experts say they’re starting to think in terms of the percentage of Americans who will be fully vaccinated. We may not get over 50 percent. So, let me ask you. I still think people want a goal, right?

Fauci: Right.

Chakrabarti: They want to know sort of how to live their lives so that we as a nation can get to a better place. So what I’m curious about is — let’s just theorize for a second, say we don’t get much beyond that 50 percent fully vaccinated. What metrics are you using? What measure are you using to say: When we hit this particular point — let’s say in deaths per day or new infections per day — that we can consider COVID no longer pandemic, but a manageable endemic disease like the flu?

Fauci: Yeah, you know, again, it depends on what you mean by the infection and what it causes. Let me give you an example: It could be that when a certain percentage of people get vaccinated, the number of hospitalizations will go down. So it may be a situation where you get people infected to get mild symptoms, but very few people get hospitalized when you have a certain percentage of people vaccinated. So you could say that that could be a certain number of hospitalizations per 100,000 population. And then you could do modeling to figure out what that is or the number of positive test case positivity. Those are the kind of things that you look at.

You know, people will give you estimates because they don’t know what the dynamics of the outbreak will be because this is such a new experience with this particular virus, particularly given the fact that we have variants that go around that may be variably protected by the vaccine. So I know people would like to know a metric. You know, the best metric is “keep going.” And when the when the numbers of infections get down to such a low level, that could be, let’s say, well, south of 10,000 per day, maybe even 5,000 per day. I mean, now, I say that and all of a sudden it becomes a sound bite. I don’t want it to be that because quite frankly, Meghna, we don’t know what that number’s going to be when you can get a real good approximation to normality. So what really people want to know is less of what that number is. [It’s] “When can I start getting my life back?”

Chakrabarti: Right.

Fauci: When can I start going out to dinner, going to the movies, going to a ball game, making sure the kids are safely in school? And that number will be when that level of infection is really very low. But you won’t know what that is. I mean, it should be, you know, in the few thousand as opposed to 30, 40, 50, 60 thousand.

Chakrabarti: Yeah. Because, you know, I get it. But like policymakers, they’re looking at those models to figure out when they’re going to feel comfortable with those numbers getting low enough so that, like you said, people can get their lives back to normal. On a normal flu year, for example, which this past year was not — but a normal flu year, let’s say, deaths per day across this country, there are 100 deaths per day. And we’ve had that rolling along for years and years and years and no interruption of the vast majority of people’s daily lives. Is that the kind of thing we ought to be aiming for regarding COVID?

Fauci: Well, you know, once we go through, I can tell you that’s what’s going to happen. We have decades and decades and decades of experience with influenza. We don’t know what it’s going to look like when you get down to 500, 400, 300, 200, 100 deaths per day. We don’t know what the impact is going to be on society, about what they’re willing to do, because you’re dealing with very different infections, very different dynamics of the infections. So I think what we have to do is — that’s why I keep saying: Let’s just push to get as many people vaccinated as possible and find out how low that is going to get us, how low in hospitalizations, how low in deaths and how low in documented, clinically recognizable infections. That’s what we need to know.

And when we know that, and we’re dealing with this virus, if we go another year or so with this. And I’m not talking about a year of a pandemic. I’m talking about we’re not going to eradicate this year. And it’s very unlikely we’re going to eliminate it. But what I do know we’re going to do, we’re going to be able to control it. And the situation is: at what level of control is society going to be able to get back to as close to normal as you possibly can?

Chakrabarti: So, Dr. Fauci, I have one more quick question here. First of all, full disclosure: My master’s degree is in environmental science and risk management, so these risk questions are — I can’t help but to ask them. I really can’t. Because especially like that’s the interface between sort of how to manage scientific and public health uncertainty with policy making decisions. Right? And I know you’ve been through the wringer over the past year, but I hear you very strenuously trying to not answer a question here. So let me rephrase it. Let me rephrase it. You’re advising the Biden administration and certainly the Biden administration — I know they’re thinking about these questions because they’ve got to make announcements. They’ve got to communicate to the people, the CDC, et cetera. What are you advising them on what they ought to be aiming for regarding … how we’re going to know when COVID is under control?

Fauci: Well, you know, that’s right. And I’m not — Meghna, I’m smiling because you’re saying that I’m trying very hard not to answer your question. I am answering your question. We don’t know what that number is. We don’t know what a number will be, when you’re going to have so control that people are going to feel comfortable about going out. I mean, we could give you a real number when there’s no infection, when you’ve actually controlled it so that they’re essentially so few infections, you could barely count them.

But we don’t know if that’s going to be the case with the dynamics. So it isn’t as if we’re avoiding your question. We don’t know the precise answer to that, because that gets to why I keep saying this elusive terminology of herd immunity. So, you know, herd immunity is when you really get the true herd immunity. We have herd immunity right now, Meghna, with measles. OK? So we have such a blanket of protection in our society that essentially nobody gets measles except when they travel from outside the country into the country. And you have such a high level of protection of people that in fact there’s no infection.

Have we eradicated measles? No, we haven’t. Have we eliminated it for the most part in this country? The answer is yes. So I would like to see that happen with COVID-19. But what we don’t know is [at] what percentage of the population are we going to get to the point where you don’t really have any COVID-19? And if you do, is it going to be like influenza where We’ll say, OK, we can live with this particular number. And that’s why I’m saying right now we don’t know what that particular number is. We can go back and just pick a number and say we’re going to stick by that number and then everyone will say, OK, we have a goal. Let’s go by that.

Chakrabarti: OK, so this is really important, Dr. Fauci, because, again, it keeps getting back to people desperately wanting to know, as you said, when can they get back to their regular lives? So we don’t know what that number is regarding COVID.

Fauci: Right.

Chakrabarti: But we’re going to have to make a — that’s actually a subjective decision, right?

Fauci: Right.

Chakrabarti: I mean, that’s kind of what you’re saying. So let me let’s just, like, change the lens on the focus on this for just a second here. What are the questions or the information or the data that public health officials, the Biden administration, et cetera, would want to know in order to help decide what that number could be?

Fauci: You know, the classic one that you’re referring to, Meghna, is the issue. And getting back to the terminology I like to stay away from, because this also is an elusive terminology, is the R0. … So when it gets less than one, and it stays at less than one, you’re going to see this essentially disappear from society. So I could tell you when the R0 goes less than one and it keeps going down, that’s where we’re going to be. But, you know, that, again, is an elusive term because the R0 really is influenced by a lot of things. It’s not inherent to the virus itself. It’s influenced by things like, you know, crowding in the situation that people are in.

Chakrabarti: So then folks are listening right now, what would you tell them in terms of how to go about their lives at this moment? Obviously, you’re going to say get vaccinated, for sure. But I think, you know, people just need to know what should they be doing now and how long could this go on?

Fauci: You know, it will change, and it will change again, depending upon the level of the dynamics of the virus in society. So right now, what you’ve seen and will continue to see is a gradual liberalization of what one can do, depending upon the level of virus in society and the number of people who are vaccinated, which will definitely influence that level of infection in the society.

For example, right now, when we were having 60,000 infections per day, the CDC, which is the larger group of epidemiologists that make these models and talk about the kinds of things you’re asking about, felt comfortable that people who were masked can now feel much safer traveling. They can be with other people who are vaccinated in the home without the masks, having physical contact. They then came out a couple of days ago as the levels started going down, and we are getting more and more people vaccinated that they could eat outdoors without a mask, that they could be doing things with outdoor activities without a mask.

And as the weeks go by and you get more and more people vaccinated and less and less infections, there’s going to be more liberalization about who can — how many people can be in a ballpark to watch a game. What about indoor dining? What about going back to the workplace? You’re going to start to see gradual liberalization of those guidelines associated with the continued diminution of the number of cases which will be profoundly influenced by the number of people who get vaccinated. And that’s why I say — and you think I’m being evasive; I’m not — “Let’s all get vaccinated,” and you’ll know it when you see it.

Chakrabarti: I suppose it’s not evasiveness, it’s the understandable uncertainty that people don’t know how to deal with. Last question. How are you doing?

Fauci: I’m doing fine. You’re wearing me down, Meghna.

Chakrabarti: Not intended here. OK, I think I hear your people saying get off the line. So let me just give you a proper thank you here. Well, Dr. Anthony Fauci, thank you so much for joining us today.

Fauci: Good to be with you. Thank you for having me.

This article was originally published on WBUR.org.

Copyright 2021 NPR. To see more, visit https://www.npr.org.