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The real reasons your family is sick right now

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Something is altering the normal seasonal currents of cold and flu viruses. They slowed to a trickle at the start of the Covid pandemic to explode human populations this year. Some public health experts have referred to it as “tripledemia”, but it could even be described as quadrupledemia.

In the northern hemisphere, the flu began surging in October, months before its normal season. This year also saw an early surge of two other viruses, RSV (respiratory syncytial virus) and adenovirus. These normally cause colds, but RSV can be dangerous for young children and has recently led to overcrowding in children’s hospitals. Adenovirus is usually mild too, but this month there were reports of the virus putting college athletes in intensive care, and it has been implicated in clusters of dangerous hepatitis cases in children.

Why now? The easy answer is that wearing masks for more than two years lowered the incidence of these viruses, and people then lost their immunity – what the popular press dubbed “immunity debt”. But that’s unlikely to be the whole story. The circulation patterns of different viruses appear to influence each other in ways that are not understood, said Michael Osterholm, director of the Center for Infectious Disease Research and Policy and host of a Covid podcast.

“When multiple respiratory viruses circulate in a given season, one will dominate for reasons we don’t understand,” he said on the podcast. “Something is going on there that can’t just be attributed to personal protection [or] distancing. »

A few other researchers made a similar observation this week in Science. “Influenza and other respiratory viruses and SARS-CoV-2 just don’t get along very well,” virologist Richard Webby told the magazine. Or as epidemiologist Ben Cowling from the University of Hong Kong put it, “A virus tends to bully others.”

This means that viral interference could be more of a factor than immune debt.

Osterholm points out that the same suppression of other viruses happened in 2009 when the H1N1 flu broke out. “For the first time in years, we did not observe any other influenza strains such as H3N2 and/or any RSV activity. He just disappeared,” he said. “It can’t be because of the mitigation, because we didn’t do any mitigation.”

He said he also doubted that the mitigation would be so effective against RSV and influenza because it was not terribly effective against Covid – more than 75% of children had been infected in February 2022. Osterholm pointed to research previous studies showing that while N95 masks work, there is much less evidence behind the types of loose-fitting cloth masks common in schools (although school closures have likely disrupted the course of other seasonal viruses).

Viral interference might offer a more complete explanation. Our innate immune system includes disease-fighting substances called interferons, which can prevent people infected with one virus from catching another. This may be why, as a large University of Glasgow study published in 2019 showed, cold viruses decrease as flu viruses increase.

Others, like infectious disease specialist Jeremy Luban of Harvard Medical School, said human behavior likely still plays a role in our changing viral currents. The lockdowns, though brief in many places, might have been enough to alter seasonal patterns. And many American schools have been closed for far longer than businesses. If we skipped a season or two of influenza, RSV and adenoviruses, populations might have less immunity to them later on.

He said it could help explain the mysterious hepatitis clusters that have sprung up in 35 countries around the world from last spring – in some cases leading to liver transplants. The latest thought, which was raised at a large meeting earlier this month, points to a co-infection of two interacting viruses.

One was adenovirus and the other an adeno-associated virus. This virus, called AAV2, needs the adenovirus to replicate. In several recent studies, almost all children with hepatitis tested positive for AAV2, but none of the children in a control group were. Similar infections could have occurred before the Covid era, but only became noticeable when the adenovirus experienced an unusual surge after Covid mitigation measures were lifted.

Biologist Andrew Read, who studies the evolution of pathogens at Penn State University, said he wouldn’t rule out dropping attenuations as a factor in the viral surges we’re seeing now. He says it’s possible that these other viruses are inherently less transmissible than SARS-CoV-2, so their spread was suppressed for a few years by the same measures that failed to contain Covid. But it’s unclear whether a year or two of reduced transmission would have a significant impact on population immunity. “We really don’t have good data on that,” he said.

He said he was particularly concerned about cases of adenovirus that have reportedly sent several University of Michigan hockey players to hospital and at least one to intensive care. “The idea that there is a problem with young people because of adenoviruses – it’s really striking,” he said. It could be a fluke – the tip of a large iceberg of mild cases of adenovirus. But it could also be something more disturbing. “We are in new territory,” he said.

This leaves the question of whether all these cases of influenza, RSV and adenovirus will leave populations flush with the interferons that could stifle the next wave of Covid. Something weird is already happening – a new omicron wave called BQ.1.1 has started, but as doctor Eric Topol writes in his newsletter, this is the first new variant that has become dominant without causing a new wave of cases or hospitalizations.

I’m cautiously optimistic that we won’t see a massive quadrupledemic this winter, if only because Covid might be crowded out by other viruses. But as we learned just a year ago, when omicron hit, Covid can still hit us with something from left field.

More from Bloomberg Opinion:

• What parents can do when RSV spikes in children: Lisa Jarvis

• How to solve the Covid test data problem: Faye Flam

• We need to develop a better flu vaccine: Lisa Jarvis

This column does not necessarily reflect the opinion of the Editorial Board or of Bloomberg LP and its owners.

Faye Flam is a Bloomberg Opinion columnist covering science. She hosts the “Follow the Science” podcast.

More stories like this are available at bloomberg.com/opinion

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