UMAIR IRFAN: This is Science Friday. I’m Umair Irfan, in for Ira Flatow.

Over the past year and a half, we’ve been talking about the COVID-19 pandemic and all the ways that it’s changed our lives. Many scientists expect that the number of infections will eventually begin to decline, but also that the virus is unlikely to go away altogether.

Instead, COVID-19 is likely to slow down from a raging pandemic to a simmering endemic disease. The virus will continue circulating and occasionally surge in sporadic outbreaks, but cases are unlikely to ever go to zero. And people will still continue to be sickened by the disease.

So what does it mean to pivot from a pandemic to endemic? And how should we think about managing these risks we’ll face over the long term?

Joining me now to talk about that is Maureen Miller, a Columbia University infectious disease epidemiologist and a medical anthropologist. Maureen, welcome to Science Friday.

MAUREEN MILLER: Thank you. Glad to be here.

UMAIR IRFAN: To begin with, let’s start by defining the terms. How is an endemic disease different from a pandemic disease?

MAUREEN MILLER: A pandemic disease is one that is certainly global, but that has a huge impact at the population level. Endemic diseases are those that hover around and occasionally make their presence known, but then can slip back into the background. They tend to be limited locally.

But because of COVID-19’s pandemic impact, that’s not going to be the case with this endemic disease, which will be floating around in the background. For example, we already have four coronaviruses that are endemic. And they are the cause of the common cold.

UMAIR IRFAN: Is there a hard line between pandemic and endemic? Or is it sort of a gradient between the two? How do you know you’re on one side or the other?

MAUREEN MILLER: In epidemiology we talk a lot about relativity. So it’s a relative line. We will know when we end the pandemic and it becomes endemic simply by the numbers of people who are getting infected and the number of people who are dying. That will change dramatically.

UMAIR IRFAN: You talked about some of these endemic coronaviruses. And there are other viruses, too, that are endemic. But influenza is sort of the classic example of a disease that has both pandemic and endemic forms. Are there other illnesses that also meet that description? And what do they have in common?

MAUREEN MILLER: Well, it’s not currently a pandemic disease, but I would say the black plague was very much a pandemic disease. And it is now an endemic disease in certain parts of the world, including the western United States, where it is harbored in animal hosts. And occasionally a person will get infected with plague.

UMAIR IRFAN: When we’re dealing with a massive pandemic that’s killing lots of people, it does seem to make sense to pull out all the stops and do everything possible to contain it. But once you shift to this pandemic stage, do those same measures make sense? Do you have to rethink the cost benefit analysis when you’re doing these precautions?

MAUREEN MILLER: When you have an endemic disease, it is usually localized in a certain area. So yeah, absolutely. There’s a different cost benefit analysis.

One of the amazing things that have resulted from COVID-19 is the creation of extremely effective vaccines. So these vaccines have the potential to last quite some time because they involve all different parts of immunity and the immune system in human beings. And they advance over time each time they get attacked by a new exposure to COVID-19.

So the fact that we have these vaccines is hugely important. Once we get vaccines available for children and we can get the entire population vaccinated, or a large chunk of it, then we’re going to see the endemicity decline tremendously. The virus will only thrive in areas where there are lower rates of vaccines. So that means what we’re going to have to do is continue to vaccinate children as they’re born and when they become eligible for the vaccine.

UMAIR IRFAN: One of the other side effects of dealing with the COVID-19 pandemic was that we saw a huge drop-off in the rate of influenza. And while a lot of people dismiss this as a fairly mild disease, between 10,000 to 50,000 people a year die from this in the United States.

So I’m wondering. Is this something similar that we’re going to have to endure with COVID-19? Are we going to have to pick a number of casualties and deaths that we’re going to face with this disease from here on out?

MAUREEN MILLER: I think all diseases have a cost benefit analysis. And unfortunately, that involves death. So yes, we will likely– if we are unsuccessful in our efforts to vaccinate a huge percentage of the population– anywhere between 85% and 95% of the population vaccinated at once– then we will see deaths.

But you just mentioned the number 10,000 to 50,000 per year of flu deaths. That’s with people vaccinated at approximately a 50% annual vaccination rate. If we can get COVID vaccinations at a much higher rate, we won’t be looking at the death rates we had in 2020, which was 350,000 US deaths.

This year, 2021, we’re on track to have anywhere between 400,000 and 550,000 additional deaths. This is not rocket science that that’s not acceptable.

If it could be comparable to flu, I think people would be not happy with that because death is terrible, especially when it can be prevented. But if we could get it to those kinds of numbers, I think the cost benefit analysis would favor allowing a certain small percentage of infected people to become seriously ill and die, unfortunately.

UMAIR IRFAN: There was a lot of talk earlier in the pandemic about this idea of herd immunity. And I’m wondering, how does that relate to this idea of the disease becoming endemic? Or are these separate concepts?

MAUREEN MILLER: No, they’re related. They’re related.

The challenge with the concept of herd immunity is what I just mentioned in terms of getting everyone vaccinated. It’s going to be impossible to vaccinate the globe for lots of different reasons– lack of access, vaccine hesitancy, outright anti-vaccination attitudes.

We will never get the high level of vaccination that we need, that we did successfully– until recently– get among measles. Measles vaccination levels were at 98% until the turn of this century. And there are lots of reasons for that change. But an anti-science bias is going to ensure that more people die than would have died had there been a much more successful vaccination coverage.

So herd immunity, I don’t think we can really discuss it in that black-and-white terminology anymore. There are too many moving parts to make herd immunity a static idea because there will always be population being born. So they will never contribute to the herd immunity. They will benefit from having people around them vaccinated. But until they’re able to be vaccinated and actually are vaccinated, herd immunity is just something that won’t exist.

UMAIR IRFAN: And you touched on this idea of attitudes playing a big role here. I would imagine that people who have endured the past year and a half of lockdowns, shutdowns, social distancing, and then getting vaccinated now being told that this disease is never going to go away– that can seem a little disheartening.

Does having this disease become endemic mean that we’ve lost the fight? Is this sort of a surrender here? Or was this inevitable?

MAUREEN MILLER: Absolutely not. Yes. This was inevitable.

It’s like flu. If you get a vaccine, it doesn’t prevent you from getting flu. It greatly diminishes the chances that you’ll get infected with flu. But it greatly diminishes the chances that you will die of flu.

So this is the same kind of dynamic that has become acceptable with flu. And we haven’t had a pandemic flu, which is one of the big contenders, which is what we– really quite frankly, we expected our next big pandemic was going to be an avian flu pandemic, much like the pandemics from the 20th century, the ones in 1918, ’19, the one in 1957, and the one in 1968.

But it didn’t happen. We had a coronavirus instead.

UMAIR IRFAN: Now, Maureen, we’ve seen pandemics in the past before. And we know of at least one disease, smallpox, that’s been completely eradicated. What are some of the key lessons to pay attention to from past global disease outbreaks like the 1918 flu or other ones that stand out?

MAUREEN MILLER: Well, the pandemic flus from the 20th century were all avian flus. So they came from animals and infected humans.

So we had no ability to fight these flus off. And in fact, two of the three flus are still in circulation in wild bird populations, and occasionally in agricultural bird populations as well.

So one of the lessons we learned about that is that because these two diseases are circulating, they’re included in flu vaccines that are developed every year. So there’s a little bit of the 1918 flu vaccination components in the flu vaccine, as well as the 1968 H3N2 flu virus.

So we’re vaccinated against them yearly if you get a flu vaccine, which I highly recommend, because as we saw when people took their masks off in the United States at the beginning of the summer, boom. There was a huge uptick in a respiratory virus that children usually get before the age of two. But pretty much everybody under age two had been in lockdown, so they weren’t exposed to these viruses and couldn’t develop immunity. So there was an enormous increase in this virus in children. There was also an enormous increase in summer colds or viruses among adults.

So if we continue to get– let’s do best case scenario– we continue to get vaccinated. We start reaching vaccination at a very high level. And we stop some of the precautions– mask wearing, social distancing– as vaccination rates improve.

Then that gives ample opportunity for flu to step in. The recommended time to get your flu shot is anywhere between the last week of September and the first couple of weeks in October. I will certainly be getting mine then.

UMAIR IRFAN: I certainly will myself. And that’s amazing to me. I had no idea that we were still vaccinating against the 1918 flu.

MAUREEN MILLER: Exactly. We are. There’s little tweaks, but the two components, the H and the N are included with tiny little tweaks in the formulation. But those viruses are still actively circulating around the globe.

UMAIR IRFAN: You’re listening to Science Friday from WNYC Studios. I’m Umair Irfan talking with Maureen Miller, a Columbia University infectious disease epidemiologist and medical anthropologist.

One of the key storylines with COVID-19, though, has been that this virus itself has been mutating and coming up with new variants that has been throwing curveballs at our vaccination campaign. And I’m wondering, is this just going to be a process of running to stand still? Does this threaten to undermine our road to becoming an endemic?

MAUREEN MILLER: Coronaviruses mutate at a much slower rate than flu viruses, for example. What we’re seeing is the enormity of the scale of people infected provide an opportunity so that it looks like mutation is occurring at a greatly increased rate. And it is, because it’s chewing through so much of the population.

So the idea that we’re setting up for a perpetual pandemic is a little dramatic because what is happening right now is that the vaccines that we have, the vast majority are extremely effective, even against Delta. They are preventing the conditions that we wanted to prevent. They’re preventing severe disease. They’re preventing hospitalizations. And they’re preventing death, the same thing that flu vaccines do.

UMAIR IRFAN: I find that very reassuring. And you mentioned the best case scenario. Right now, though, it seems that all across the US and across the world, different countries have different approaches to dealing with COVID-19, ranging from basically ignoring it to giving it the full court press with vaccines. And I’m wondering, how does that start playing out as far as ratcheting down on the pandemic?

MAUREEN MILLER: I think various countries– I mean, Singapore in the lead because they had very good control. They were going for a zero-tolerance COVID-19 acceptance. And that’s just not realistic. We are so interconnected in the globe that that’s just not realistic.

So New Zealand is hoping for that. Singapore was. Taiwan was. China certainly still is.

That’s just not realistic because you can’t keep your borders closed forever. And that would be a horrible thing to result from COVID-19, if certain countries chose to not allow border passage of their citizens out or other citizens in. That just doesn’t function in a global economy. And countries that choose to do that have historically had real challenges in growing their economies and in providing care and support for their populations. It just doesn’t work.

UMAIR IRFAN: But if countries did work together and harmonize their policies, could we find our way out of this sooner?

MAUREEN MILLER: [LAUGHS] Well, I’m not quite sure how to answer that question because even in the face of a horrible pandemic that’s killing so many people around the globe, we’ve still failed to harmonize.

And part of that is because it’s a whack-a-mole. It pops up and does devastation in India, and then just dramatically disappears. And we don’t know why.

And then, of course, it travels. It travels to England where it does the same thing– pops up, devastation, and then dramatically disappears. Goes to Europe. I mean, we watched the show of waves so many times when it first came from China. Suddenly it was in Iran. It was in Italy.

And the rest of the world thought, oh, it’s not going to come here. We certainly thought that in the United States. And then it did.

Then with this next round of the Delta variant from India, hit Europe, and we thought, oh, we’re home free in the US because we have 50% of our population vaccinated.

It doesn’t work that way. It crosses borders whether you close them or not.

UMAIR IRFAN: And finally, I’m sure nobody wants to think about this right now, but what lesson should we take from this pandemic and apply ahead of the next one?

MAUREEN MILLER: We should– because there will be a next one, we should really focus on preventing the next pandemic. And there are– we have tools that can do that right now.

What we need to do is go to the global hotspots where we know zoonotic disease spillover is happening and is likely to occur and is likely to be the source of our next pandemic, and monitor populations for zoonotic disease spillover. It’s a really simple process. It’s not one that’s been widely adopted. But Benjamin Franklin– “an ounce of prevention is worth a pound of cure.”

But we’re so medicalized in our society. For example, the 900-year-old techniques that are known to work– social distancing and mask wearing– they’ve been reframed as non-pharmaceutical interventions. So already, something that’s been successful for almost a millennia has been reduced to second class, relative to pharmaceutical interventions.

So I think it’s going to be a hard sell to try to prevent. Even now, people don’t talk about prevention. They talk about preparedness and response. By the time you’re responding with a disease like COVID, which is stealthy and it explodes even before you know what’s going on, preparedness and response will never be enough.

UMAIR IRFAN: Well, I hope everyone takes those lessons to heart. Maureen Miller, infectious disease epidemiologist and medical anthropologist at Columbia University, thanks so much for talking with me today.

MAUREEN MILLER: Thank you for having me. It was a pleasure.

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