As respiratory syncytial virus, or RSV, infections have packed pediatric hospital beds around the country, there has been no shortage of people — experts and laypeople alike — speculating as to the potential causes.

One of the theories circulating blames previous COVID-19 infection in kids for their increased susceptibility to severe RSV. Another takes a widely accepted explanation — diminished immunity due to less viral exposure over the last two-plus years of COVID precautions — and co-opts it to condemn public health measures meant to contain COVID, while blaming them for sky-high numbers of RSV hospitalizations in kids.

”All these things have a little bit of partial truth,” says Dr. Scott Krugman, vice chair of the department of pediatrics at Herman & Walter Samuelson Children’s Hospital at Sinai.

So, what is behind the current RSV surge in kids? And how do we tell where science ends, and speculation and agenda pushing begins?

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One theory making the rounds on social media blames previous COVID infections for causing immune damage or “dysregulation” and making kids more susceptible to severe RSV. Krugman understands the thought process behind this claim, he said, since “we have been a little surprised and quite impressed with what COVID can do to bodies and to immune systems.”

Still, he cautions it is purely speculative at this point and not backed up by any data. The immediacy of the RSV surge also means that collecting and analyzing this data is a way off.

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Krugman notes that there are ways in which COVID has been proven to wreak havoc on the immune system, with perhaps the most extreme example being multisystem inflammatory syndrome in children, or MIS-C, a dangerous yet rare post-viral immune response occurring weeks after a COVID infection. But, research to date has not identified any clear mechanism showing that COVID infection causes immunosuppression. This stands in contrast to a condition like HIV, Krugman said, which we know kills T-cells and with them the body’s ability to fight off disease.

As for long COVID, it’s currently unknown whether the disease is a prolonged infection or a sustained reaction to the acute form of the virus, Krugman said.

Dr. Ashanti Woods, pediatrician at Mercy Family Care Physicians, agrees that while COVID undoubtedly impacts the immune system in some way — evidenced by patients whose immune systems “went haywire” before they ultimately succumbed to the disease — the scientific community does not yet know precisely what those effects are, especially over the long-term. That research is in progress now, Woods said. He feels it is “unlikely” that COVID after-effects are behind the RSV surge.

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Woods’ skepticism is shared by Dr. Andrea Berry, pediatric infectious diseases specialist at University of Maryland Children’s Hospital. Any connection between RSV and previous COVID infection is simply “a hypothesis,” she said, that currently lacks any evidence to support it.

All three experts point to a different cause for the unprecedented spike in RSV cases: lowered immunity from less viral exposure over the last two-plus years, due to widespread COVID precautions. Many infants and toddlers have had virtually no exposure to common viruses such as RSV since birth, Woods said, and kids under 3 years old are the ones most susceptible to developing a case severe enough to warrant hospitalization, in any year — not just during the current surge.

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Krugman said RSV can be particularly concerning in babies and toddlers because it “creates inordinate amounts of mucus” that their small airways can’t handle, and they can have difficulty eating and breathing as a result. There is also no vaccine to prevent RSV and no medication designed to treat it, Krugman said — another thing that sets it apart from other respiratory illnesses, such as the flu and COVID.

And now, since immune systems have been on “chill mode” for some time, Woods said, kids of all ages have not developed the immune defenses that usually protect a greater number of them from getting sick, and from contracting severe illness.

However, this widely accepted explanation has been harnessed by some on social media to condemn COVID precautions — particularly the use of masks — by arguing that the prolonged reduced exposure that these precautions made possible is to blame for the explosion of RSV hospitalizations among kids. These individuals feel this lack of exposure has weakened immune systems, likening them to a muscle that, if not exercised, cannot perform at its best.

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Krugman said this analogy is “not a good understanding” of how the immune system works.

“If that were the case then the same people would be very much in favor of vaccines because vaccines are like training wheels for the immune system,” he said. “More kids are more susceptible because they haven’t been exposed to viruses, and that has nothing to do with their immune systems.”

Berry observes that people criticizing masking and other precautions in the context of the RSV outbreak “don’t remember what spring of 2020 was like,” when COVID vaccines and treatments did not exist; dozens of people were hospitalized for the virus at University of Maryland Medical Center alone; and masks and other precautions were the only lines of defense against a potentially fatal virus.

“Masking was the correct decision for the situation that we had,” Woods said. “And so to that person that says, well look at us now, our kids and grandkids are susceptible to all these viral infections, I would say to them you have the privilege of making that comment now because you survived,” likely thanks to the precautions that were in place, he said.

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Regardless of its cause, local experts say no one knows how the rest of the respiratory virus season — which is generally regarded to last through most of spring — will play out. All are hopeful that the early, sharp peak of RSV hospitalizations means that the rest of the season will be mild, at least for that illness — similar to a “bumpy roller coaster ride” that’s intense for a short period and then stops, Berry said. Flu numbers have skyrocketed and COVID is on the rise, the experts say, but both illnesses are far less likely to land children in the hospital compared to RSV.

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RSV hospitalizations hit a statewide peak of 257 at the end of October, and they’ve fallen nearly two-thirds to 88 four weeks later, per the most recent data, but these numbers are still in line with peaks in some previous years. Woods cautions that although the surge has abated somewhat, pediatric beds remain 85 to 90% full.

The fact that the current RSV season has followed a “very atypical pattern,” with cases cropping up all summer long, followed by a massive early explosion and then a sharp and sudden decline — versus the usual more gradual downturn — means the rest of it will be harder to predict, Krugman said. The remaining months could be characterized by low-grade circulation, he said, or we could have another spike over the winter.

“We’d love to dust our hands off and say okay great, no more RSV, but we know not to do that,” Woods said.

Sarah True was a public health reporter for the Baltimore Banner. She previously worked as a freelance journalist covering healthcare and health policy, and has been both a medical social worker and a health policy analyst in a past life. She holds dual Master’s degrees in public health and social work.

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