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This winter's U.S. COVID surge is fading fast, likely thanks to a 'wall' of immunity

Immunity Americans acquired through vaccination or via prior infection with the SARS-CoV-2 virus may account for the lighter than expected COVID surge in the U.S. this winter, researchers say.
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Immunity Americans acquired through vaccination or via prior infection with the SARS-CoV-2 virus may account for the lighter than expected COVID surge in the U.S. this winter, researchers say.

This winter's COVID-19 surge in the U.S. appears to be fading without hitting nearly as hard as many had feared.

"I think the worst of the winter resurgence is over," says Dr. David Rubin, who's been tracking the pandemic at the PolicyLab at Children's Hospital of Philadelphia.

No one expected this winter's surge to be as bad as the last two. But both the flu and RSV came roaring back really early this fall. At the same time, the most contagious omicron subvariant yet took off just as the holidays arrived in late 2022. And most people were acting like the pandemic was over, which allowed all three viruses to spread quickly.

So there were big fears of hospitals getting completely overwhelmed again, with many people getting seriously ill and dying.

But that's not what happened.

"This virus continues to throw 210-mile-per-hour curve balls at us. And it seems to defy gravity or logic sometimes," says Michael Osterholm, who heads the Center for Infectious Disease Research and Policy at the University of Minnesota.

"People all assumed we would see major transmission. Well, every time we think we have some reason to believe we know what it's going to do, it doesn't do that," Osterholm says.

'The worst' of the surge of COVID, flu and RSV may be over

Infections, hospitalizations and deaths did increase in the U.S. after New Year's. But the number of people catching the virus and getting hospitalized and dying from COVID soon started to fall again and have all been dropping now for weeks, according to the latest data from the Centers for Disease Control and Prevention.

The fall flu and RSV waves continue to fade too. And so the worst looks like it's probably over, many public health experts say.

"I'm glad to say that we didn't have as much of a crush of infections as many thought was possible, which is very welcome news," says Jennifer Nuzzo, who heads the Pandemic Center at Brown University.

The big question is: Why? Several factors may have played a role.

One possibility could be that people avoided crowds, wore a mask and took other precautions more than public health experts had expected they would. But that doesn't really appear to be the case.

Might 'viral interference' play a role?

Another possibility is "viral interference," which is a theory that sometimes when a person gets infected with one virus, their immune response may protect them from getting infected with another virus. So maybe RSV and flu crowded out COVID in the same way COVID crowded out those other viral infections at various times over the last two years.

"At this point, I think that's more of a guess rather than very solid evidence," Nuzzo says. "But if it's true, that might mean we might be more susceptible to seeing a rise in infections when those viruses are not around."

Nuzzo and other experts suspect instead that the main reason the COVID surge is ebbing is all the immunity we've all built up from prior infections, and/or the COVID vaccinations many of us have received.

"We have what I would call now a better immunity barrier," says Dr. Carlos Del Rio, an infectious disease specialist at Emory University who heads the Infectious Disease Society of America.

"Between vaccinations and prior infection I think all of us are in a different place than we were before," he says. "All of us, if not totally protected, we are somewhat better protected. And that immunologic wall is real."

"Make no mistake: COVID-19 remains a significant public health threat. ... The fact that we are still losing hundreds of people a day to this virus is deeply troubling."

Why COVID-19 remains a significant threat

But none of this means the country doesn't have to worry about COVID anymore. More than 400 people are still dying every day from COVID-19. That's far fewer than the thousands who died during the darkest days of the last two winter surges. But it's still many more people than die from the flu each day, for example.

"Make no mistake: COVID-19 remains a significant public health threat," Nuzzo says. "That has not changed. And the fact that we are still losing hundreds of people a day to this virus is deeply troubling. So we shouldn't have to accept that level of disease and death that we are seeing."

William Hanage, an epidemiologist at the Harvard T.H. Chan School of Public Health, agrees.

"It's beyond question that society has moved into a stage where the pandemic is for most of us if not over then certainly quiet. And that's a great thing. Long may it remain so," Hanage says. "Is it the case that there is no preventable suffering? No. There is still preventable suffering and death."

Most of the people dying are elderly, many of whom have not received the latest booster against COVID-19. So getting them boosted could help a lot. And the immunity the rest of us have built up could keep fading. That means many of the rest of us may at some point need to get another booster to help further reduce the threat from COVID.

Another wave of flu could still hit this year, public health experts note, and the risk continues that yet another new, even more dangerous variant of SARS-CoV-2 could emerge.

"This virus isn't done with us yet," Osterholm says.

Copyright 2023 NPR. To see more, visit https://www.npr.org.

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Rob Stein is a correspondent and senior editor on NPR's science desk.