People are blaming “immune debt” for the “triad” of RSV, flu and COVID that is hitting children across the country. But experts say that’s misguided at best and could even be harmful

This fall, North American children are not okay.

Children’s hospitals are filled with an unusually high number of patients sick with several different viruses – mainly RSV, flu and COVID, but also flu-like viruses such as rhinovirus and enterovirus. Many are at or near capacity, and some are well beyond capacity, having made room for patience in offices, gift shops, playgrounds and parking tents.

Parents, pediatricians and public health officials are asking the same question: How did we get here?

One popular idea that has emerged in the public health community: The increase is due to “immune debt,” a recently coined term. According to the theory, kids were exposed to fewer germs — COVID and others — over the past three years because of pandemic precautions like masks and social distancing, and their immune systems weakened. Now that society has reopened, children face the usual petri dish of viruses with weakened defenses, causing an onslaught of illness – and perhaps more, and more severe, illness than would otherwise have occurred.

But experts Fate spoke to say the theory is at best unscientific and at worst destructive, disagreeing with any argument that COVID precautions have harmed the immune system and highlighting a variety of factors leading to the current “triple bleed.”

What is Privacy Debt?

When it comes to why kids are getting hit with viruses this fall, immune debt is “definitely the most popular hypothesis going around,” said Dr. Lael Yonker, Harvard Medical System assistant professor of pediatrics at Massachusetts General Hospital, said Fate.

The general idea is that babies born during the pandemic were protected from viruses they would normally have been exposed to if they interacted with more people – and that this weakened their defenses.

“These kids are now one-year-old, two-year-old, and they haven’t seen RSV before,” she said. “They haven’t built immunity in general and now they’re getting really sick.”

The theory of privacy obligations was first proposed by French researchers in an opinion piece in 2021 in Infectious diseases now. Pandemic precautions such as masks and social distancing prevented hospital systems from being overwhelmed in the near term, flattened the so-called COVID curve and dramatically reduced the spread of other pathogens. But they increased the likelihood of future epidemics, the authors wrote, “because of the increasing proportion of ‘susceptible’ people and reduced herd immunity among the population.”

Since the article was published, discussion of the term has exploded, reaching from medical journals to Twitter and news outlets.

But some say the debate has turned from scientific to political, with opponents of the mask using the theory to try to prove that covering up causes harm.

Dr. Amesh Adalja, an infectious disease expert and senior fellow at the Johns Hopkins Center for Health Security, believes the term is “misused and misinterpreted” and that it is “creating unnecessary political conflict on social media.”

“I don’t necessarily like ‘immunity debt’ to be a phrase,” said Dr. Sarah Combs, an emergency physician at Children’s Hospital in Washington, DC, said Fate.

“We know there was a lot of politicization during the pandemic and I’ve seen some people pick up on that [the term] and say: Ah ha! This proves that we were doing it all wrong, that the mask was bad, and that we should never do it again.'”

“I will come out and say that this is completely false. Using this as rhetoric that says, “There was clearly no need for public health action,” doesn’t work. It’s harmful.”

Dr. Jason Catanzaro, a pediatric allergist and immunologist at National Jewish Health in Denver, notes that masks were much less common in some parts of the country — and yet children in those states are struggling just as much now during the triplets.

“As far as I can tell, there is not a significant area of ​​the country — red or blue — that is spared from RSV,” he said.

“Our immune system worked just fine”

Several experts who Fate spoke to say that “immunity debt” is not the reason why pediatric wards are overflowing with patients this year.

It’s not really a scientific term, Dr. John Bradley, chief of infectious disease medicine at Rady Children’s Hospital in San Diego and distinguished professor at the UC San Diego School of Medicine, says Fate. And children’s immune systems didn’t stop working during the pandemic, says Catanzaro.

“They were still monitoring cells for cancer and interacting with trillions of microbes constantly to figure out which bacteria were good and which were bad,” he said. “Our immune system was working just fine.

Instead, Bradley and Catanzaro believe the increase is largely driven by the huge pool of children with healthy immune systems all reentering the community at the same time. Their immune systems were not weakened, but they may not have received their regular annual vaccinations, or immunity is “boosted” by exposure to non-vaccine viruses such as RSV, they say.

Catanzaro likens an American children’s group to a young child who goes to daycare for the first time — and spends the next few months catching what seems like every illness under the sun.

“Would that be considered a breach of confidentiality?” he asked. He described how his daughter went through the common scenario of transitioning into childcare before the pandemic. “I don’t think her immune system was weak.” She just hadn’t seen these things before.”

Lots of potential factors – and even more questions

Experts say there could be a myriad of factors behind the children’s “three bleeds” – and most of them are not viral.

Hospitals are short staffed and relatively few hospital beds for children in the United States. Vaccination rates among children have also declined in recent years, leading to more infections. And this could also be a worse than average flu year. The same may be true of RSV, which may have evolved to be more potent than it once was.

But some experts like Catanzaro and Yonker say more could be at play this fall. Many North American children returned to their own studies last year, mostly without masks, and the continent did not see the same increase in hospitalizations that it is seeing now.

“Tons of people were diagnosed with RSV in the middle of a pandemic, and there weren’t mass hospitalizations,” Catanzaro said.

“We weren’t closing ICUs and filling hospitals,” Yonker added.

Both say it’s possible that COVID – which has infected the majority of the world’s population – has taken a toll on the immune systems of those previously infected, the way measles can. COVID can alter the production of interferon, a substance produced by the body that helps the immune system fight infections and diseases such as cancer, according to Catanzaro.

So far, there is no evidence to prove this theory. But measles in unvaccinated children can “lead to immune memory,” Catanzaro said, citing a 2015 paper in Science who “demonstrated that measles wipes out pre-existing immunity to previous viruses.

Bradley expects viruses like the flu and RSV to return to their normal seasonal patterns within a few years. And he expects COVID will eventually follow suit.

Still, the question of what caused the trifecta is—and will remain—more than an academic exercise for the millions affected this winter.

“There are a lot of people out there whose kids are on oxygen with RSV who want an answer,” Catanzaro said.

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