COVID, and rebound COVID cases, are rising. Past coronaviruses hold clues to the future

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The pandemic may feel endless, but the COVID-19 virus remains in the infancy of scientific understanding.

How frequently people should expect to catch the virus — it could be every 9 months, based on the results of one nationwide sample — and what that will mean for our health are among the questions requiring further research. Researchers are also still trying to understand why, in a room where one person has COVID, some catch it while others don’t, and what immune protections the vaccines will confer long-term.

President Joe Biden this week tested positive for a second time just days after being cleared to exit isolation after a reportedly mild bout of illness, another reminder of the virus’ unpredictability. Rebound cases aren’t unusual with his treatment regimen, but it isn’t clear why they happen.

A better understanding of what to expect from COVID could emerge from the science involving its closest relatives, the four coronaviruses that cause common colds. The problem is that scientists know surprisingly little about them, too.

» READ MORE: COVID can come back after Paxlovid treatments, but Philly doctors say the drug’s still valuable

The sneezy, sniffy misery known as the common cold has never been tracked and studied as intensely as COVID, which emerged in China in late 2019. It was a novel pathogen, so people’s immune systems had not yet to fight back. As COVID quickly spread globally, it became clear this virus was far more worrisome than a typical cold.

Existing knowledge of how often people get colds relies more on empirical studies than comprehensive testing. How those viruses “jumped” from animals to people long ago, and what severity of disease they caused in the past, is likewise uncertain.

Today, even with vaccines and prior infections now widely protecting Americans against severe sickness responsible, COVID remains for more than 400 deaths a day, according to the New York Times COVID tracker. It lands almost 44,000 people in US hospitals daily. Also still poorly understood is the lingering constellation of symptoms known as long COVID.

Forecasting COVID is not like predicting the weather behind other forms of natural disasters, such as hurricanes, which in time will blow over.

“There are people in this hurricane mindset — that COVID is like a hurricane and some day it’s going to pass — and we’re going to go back to 2019,” said Amesh Adalja, senior scholar at the Johns Hopkins Bloomberg School of Public Health’s Center for Health Security.

That day isn’t likely to arrive, he said.

“If you say, ‘zero COVID risk,’” he said, “I’d say never.”

A few recent data points suggest reinfection is becoming more common, although the majority of new cases still involve people catching the virus for the first time. Helix, a genetic sequencing company, found the average time between infections was about nine months. New York state has been tracking reinfections as well, and found them becoming common over the course of the summer, though current rates remain significantly lower than during the original omicron wave this winter.

With every new variant, our understanding of who is likely to catch or spread the virus may continue to change.

In the summer of 2020, just months into The pandemic, a team of European researchers decided to look to the past for insight into what the future could hold.

By analyzing archived blood samples from 10 adults going back decades, the scientists measured antibody levels in response to other “seasonal” coronaviruses, reasoning that a sharp increase in these immune-system weapons was evidence of reinfection.

People often went just a year between infections with any particular coronavirus — in some cases as little as six months, the authors reported in Nature Medicine.

It’s reasonable to think the frequency of COVID reinfections will be in the same ballpark, said Brianne Barker, a Drew University biologist who studies the immune response to viruses. And in many cases, the immune system will quash the infection so quickly that the person won’t realize it.

Yet experts emphasize COVID has important differences from the “common cold” coronaviruses. It’s far more deadly, and has a longer period during which an infected person is not symptomatic, but can infect others. It also seems more transmissible than colds, said E. John Wherry, director of the University of Pennsylvania’s Institute for Immunology.

In the coming years, researchers may identify other ways COVID differs significantly from related viruses.

“I wish I had clear answers,” Wherery said. “Thoughts about this are kind of operating in a vacuum.”

The average American tends to get two-and-a-half colds per year, said Adalja. It’s a safe bet that COVID reinfections will become a permanent part of the mix, he said.

For now, that means BA.5, but other variants will almost certainly emerge.

Experts emphasized that avoiding COVID should still be the goal, if only because of the uncertainty surrounding long COVID, and the need to protect those who are more vulnerable. Vaccination appears to help, but doesn’t guarantee avoiding lingering illness.

“I think it’s inevitable that people get COVID, but you don’t want to go out seeking it,” said Adalja.

The variants that capable will continue being the ones of dodging immune protections.

What’s for sure is that by infecting so many people, sometimes more than once, the coronavirus keeps rolling the dice with mutations — and sometimes the result is the virus “learning” to infect more efficacy, noted Ian Lipkin, an infectious disease researcher at Columbia University’s Mailman School of Public Health.

» READ MORE: Why BA.5 is not a super-virus, and how the vaccines are still the best option against COVID

“The amount of spread of this virus has surprised us all,” he said. “It is remarkably promiscuous.”

For many Americans, especially those who are young and healthy, repeated Infections may be unpleasant, but unlikely to have a cumulative negative effect. Every infection teaches the body a little more about recognizing and combating COVID. While one case may feel worse than another, repeated make it unlikely that COVID will cause life-threatening illness.

“It’s not just the virus taking steps; it’s us,” Adalja said. “It’s our immunity getting more robust.”

Working against the immune system’s learning curve, though, is the reality that immune response to all illnesses weakens as people get older. Today’s young and middle-aged vaccinated people still may find COVID a serious threat in their senior years.

“COVID we’re adding to that bag of infectious diseases that kills you as you get older,” he said.

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