COVID’s endgame: Scientists have a clue about where SARS-CoV-2 is headed

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29 Окт 2021, 21:54

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Hanna Barczyk for NPR

Shots — Health News
This Coronavirus Doesn’t Change Quickly, And That’s Good News For Vaccine Makers

Then in December 2020, right around the holidays, SARS-CoV-2 shifted course, drastically.

Scientists in South Africa announced that they had detected a mutant version of the virus that seemed capable of reinfecting people — that is, avoiding the immune response created by a previous infection. A few weeks later, scientists in the U.K. identified a rapidly spreading mutant that looked to be about 50% more transmissible than the original versions of the virus. A few weeks later, another mutant cropped up in Brazil, causing a massive second surge then.

An unexpected change in the course of SARS-CoV-2

So all of a sudden, it looked like SARS-CoV-2 not only was mutating but was doing so quite rapidly. Last month, Kistler and her colleagues at the University of Washington published a new metric to measure how quickly SARS-CoV-2 is evolving as it adapts to living inside humans. When Kistler first saw the value, she was shocked. «SARS-CoV-2’s rate of adaptation is remarkably high right now,» she says, «like roughly four times higher for SARS-CoV-2 than it is for seasonal flu.»

Remember, the flu changes so fast that people can be vulnerable to it each year.

«I don’t think SARS-CoV-2 will stop adapting,» Kistler says. «It may slow down, but viruses that evolve adaptively tend to keep doing that. They don’t tend to hit the limit of evolution.»

This fast evolution has immense implications, many scientists say. It essentially dashes the hopes of eradicating SARS-CoV-2 in the U.S. or even in smaller communities. As with the flu, the coronavirus will likely be able to reinfect people over and over again. It will keep returning year after year.

«Eventually everyone will be exposed to SARS-CoV-2,» says Dr. Abraar Karan, who’s an infectious disease specialist at Stanford University. «It’s a matter of whether you’re exposed when you’re fully vaccinated or when you’re not vaccinated.

On the surface, these findings sound like horrible news. It sounds like the COVID pandemic — along with the masks, physical distancing and quarantining — will never go away.

But Karan doesn’t believe that will be the case. Although he predicts that SARS-CoV-2 will circulate in the U.S. indefinitely, he says that COVID, the dreadful disease, as we now know it, will likely go away.

«When you’re fully vaccinated [or been exposed several times], you’re dealing with a very, very different disease and a very different process,» Karan says. In fact, you’re likely dealing with a disease that many of us have already had, perhaps dozens of times, in our lifetimes.

You’ve caught coronaviruses many, many times

This might come as a surprise, but the U.S. has dealt with many — and massive — coronavirus outbreaks before the COVID pandemic.

Besides SARS-CoV-2, there are four other coronaviruses in widespread circulation, named NL63, 229E, OC43 and HKU1. The first two have likely been infecting people for centuries. And the latter two for decades, perhaps longer. They’re related to SARS-CoV-2 but are not the same.

Each year one or more of these other coronaviruses sweeps through the U.S — in schools, daycare centers, churches and offices — and makes people sick. Many, many people. These coronaviruses are so common that by the time a child starts kindergarten, they’ve likely been infected with all of four of them.

Virologist Rachel Eguia at the Fred Hutch research institute in Seattle and her colleagues have been studying one of these coronaviruses.

«So we’ve been studying strains of a coronavirus from 1984, 1992, 2001, 2008 and 2016,» says Eguia. She wanted to see if people could get reinfected every eight years or so.

Here’s the sneaky thing about these coronaviruses: Just because you caught one of them last year doesn’t mean you’re protected from that same coronavirus infection the next year.

Remember that British experiment described at the beginning of this piece, in which volunteers had virus particles injected up their noses, not just once but twice? In that study, the researchers also measured people’s antibodies in their blood before the second exposure to the virus. They found that having antibodies against that specific virus didn’t necessarily protect people from being infected the second time — but there was a benefit nonetheless. Having higher antibodies levels prevented people from developing symptoms altogether and shortened the time they spread the virus.

«Several studies suggest that every few years you’re probably able to get reinfected with these coronaviruses,» Eguia says. A study, published last year in Nature Medicine, found that immunity to these seasonal coronaviruses lasts less than 12 months. Throughout a person’s lifetime, they’ve likely caught them several dozen times.

Yet nobody notices them. We catch these coronaviruses, and «normal» life goes on. Schools and churches stay open. People gather inside bars and clubs. House parties continue. Why? Because these coronaviruses typically cause only colds. They give you the sniffles, a cough, some sneezing, congestion, maybe a low-grade fever. The illness is generally milder than the flu and resolves on its own in a week or so.

Together these coronaviruses cause about 10 to 30% of all colds in adults, studies have found. So in many ways, these coronaviruses are part of modern life. We simply coexist with them, without much fanfare.

Could the same be true for SARS-CoV-2?

Could SARS-CoV-2 Become A Common Cold?

Some scientists are starting to think that eventually COVID could turn into a disease that looks more similar to these other coronaviruses — in other words, a mild flu-like illness.

«That’s what our computer models predict,» says Jennie Lavine at Karius. For the past year and half, she and her colleagues have combined what’s known about the four other seasonal coronaviruses to try and forecast what SARS-CoV-2 will do two, five and even 10 years from now. They published their findings in the journal Science last February.

For the new virus to turn into a mild cold, she says, two conditions need to be met. First off, immune protection against severe disease has to persist. «Being infected a few times or having a few doses of the vaccine needs to provide really long-lasting immunity against severe disease,» she says. It doesn’t have to prevent transmission or a mild disease. But it has to keep you from being hospitalized.

After the vaccine, so far, immunity looks like it’s holding up for at least six months or so for healthy adults, says Rustom Antia, a colleague of Lavine’s at Emory. But right now it’s unclear how long that critical immunity will last for people more at risk for severe disease.

«We don’t know how it will hold up for older individuals, above 60 or so. «We don’t know how many doses of the vaccine will be needed to build up our immunity so that when we do get infected naturally, it’s not severe.»

But if the vaccine — and/or natural exposure — does provide long-lasting immunity for everyone, over time, the vast majority of the population would eventually be protected against severe COVID. That would leave only one population unexposed and vulnerable: Brand-new people — newborns.

And that brings us to the second condition required for SARS-CoV-2 to become a seasonal cold: The virus has to continue to be relatively mild in kids.

Although children and babies can, in rare cases, experience dangerous complications, in general, COVID poses low risk to young children. Although the reason for this decreased risk is unknown, one study, published in August, showed children’s immune cells in their noses can more quickly detect SARS-Cov-2 than the corresponding cells in adults — and take action to ward it off. The data suggest that «immune cells of the upper airways (nose) of children are pre-activated and primed for virus sensing,» the authors wrote.

As long as SARS-CoV-2 continues to be low risk in children — that is, as long as a new variant that’s dangerous to kids doesn’t emerge — then they can get infected early on when they’re young, build up their immunity to the virus and have protection from severe disease as adults. So in theory, everyone around the world would eventually be protected from the horrible disease that COVID can become.

Now, the buildup of this immunity across a whole population can take time — perhaps years. That’s why, Antia says, it’s so important for people to get vaccinated because the faster everyone is protected against severe disease, the faster COVID could transform from a disease that causes great fear to a disease that fades into the background of our lives.

Of course, as with all predictions about viruses, this one could be completely wrong. Over the past year and a half, SARS-CoV-2 has surprised even the smartest — and most skeptical — scientists. But the more researchers learn about our immune response to SARS-CoV-2, says Paul Bienaisz, the more optimistic he becomes that this endgame scenario (or a variation of it) will come true. «Based on what we’re finding, it does look like the immune system is eventually going to have the edge over this virus.»