DAVID GREENE, HOST:
It is called herd immunity, and it's a concept some leaders and scientists have considered when it comes to responding to this pandemic. NPR's Geoff Brumfiel reports on what exactly this idea is and why it presents troubles.
GEOFF BRUMFIEL, BYLINE: The thinking goes like this. Sooner or later, the pandemic has to end. And Devi Sridhar gets it.
DEVI SRIDHAR: Like, everyone wants a way out psychologically - right? - because no one's ever coped with something of this scale. And it's not like a crisis like a hurricane or 9/11 where it's, like, time-bound or geographically bound. This is, like, everyone, everywhere for indefinitely - right now, it feels to people, right?
BRUMFIEL: Sridhar is a researcher at the University of Edinburgh Medical School in the U.K. And it turns out there is a theoretical way it could end. If enough people get sick and recover and they become immune to the coronavirus, then the pandemic fizzles. Those who haven't gotten it yet are safe. The technical name for this is herd immunity. In its purest form...
SRIDHAR: It's like Darwinian self-selection, right? We let the virus go. Whoever is going to die will die. That's life. And then whoever makes it will have, hopefully, some form of immunity.
BRUMFIEL: Several governments toyed with the idea at the beginning of the pandemic, including the U.K., but in the end, most decided it would cost too many lives. There was one exception - Sweden. They kept businesses open and let people make their own choices. At one point, Swedish officials said Stockholm would reach herd immunity by the end of May. But...
SRIDHAR: They have not reached it by the end of May. They just lost a lot of lives and also took an economic hit.
BRUMFIEL: Sridhar says herd immunity works as a math problem. But at an individual level, Swedes stayed home. People don't want to catch COVID.
SRIDHAR: Nobody wants to be part of the herd. (Laughter) Let's just say it that way.
BRUMFIEL: But could nations eventually reach herd immunity more slowly? Probably not, says Jeffrey Shaman of Columbia University.
JEFFREY SHAMAN: So an example I like to think about is South Korea. They're getting 50 cases a day right now. If they were to hold on for another thousand days, which is almost three years, they'd have 50,000 cases, which is 0.1% of their population.
BRUMFIEL: Most experts think herd immunity takes somewhere between 50% to 80% of the population. Even in the U.S., even at 60,000 cases a day, it'll take at least into 2021 and possibly years more to reach those levels.
And there's another looming problem. People may be able to get the coronavirus more than once. Shaman has studied other coronaviruses that cause common colds, and he found people could be reinfected.
SHAMAN: Some of them were four to eight weeks separated from the previous infection, which is rapid, and that might've been a relapse. But others we clearly know are different. They were eight to 11 months apart.
BRUMFIEL: Greta Bauer is an epidemiologist at Western University in Ontario. She says this fall and winter may be the time we find out about reinfections. And if COVID survivors get even mildly sick the second time around, coronavirus will keep circulating.
GRETA BAUER: If that were the situation, then there's no potential to develop a level of herd immunity sufficient to stop the infection.
BRUMFIEL: I corresponded with 16 different scientists, and almost all believed that achieving herd immunity as a practical matter was virtually impossible without a vaccine. With a vaccine, it will be a lot easier to control the virus, but it will likely still exist in pockets around the world.
So what's going to happen? Again, researcher Devi Sridhar.
SRIDHAR: I think it's going to be with us probably forever at this point. I mean, at a global scale, it's going to be with us, and it's how we decide to live with it.
BRUMFIEL: There are ways to live with it. Test the sick. Isolate them until they're better. And everybody wear a mask and keep their distance.
Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.
