SALT LAKE CITY – While COVID-19 transmission rates continue to decline, two illnesses that normally result in many pediatric hospital admissions are nearly non-existent all winter.
Respiratory syncytial virus, or RSV, and influenza have resulted in virtually no hospital admissions at Primary Children’s Hospital. This is a welcome surprise to pediatric specialists who typically deal with 80 to 120 RSV hospitalizations and dozens of intensive care unit stays per week, in addition to hundreds of annual hospitalizations for influenza.
“This is really remarkable,” said Dr. Andrew Pavia, pediatric infectious disease specialist at Primary Children’s Hospital, at a news conference Monday on the trends in pediatric hospitalization for both viruses.
The hospital has seen more cases of the rare complication of SARS-CoV-2, called multisystem inflammatory syndrome, in children, or MIS-C, than flu or RSV. It is estimated that about 75 MIS-C cases have been treated in the hospital in recent months.
RSV is something that affects “almost every child” in the early years after birth. It usually results in coughing and wheezing; some children become short of breath and need to be hospitalized.
Adults over 75 also suffer from RSV. Pavia said it ultimately results in much older cases of pneumonia. Older children and adults typically experience cold symptoms from it.
The primary children’s hospital has still not reported any RSV hospitalization during the typical season.
“We’re seeing something I’ve never seen for the past 35 years,” said Pavia. “If you go back to history, it didn’t really happen, except shortly after the 2009 flu pandemic.”
Then there’s the flu, which often affects hundreds of thousands of Americans every year. So far, the Centers for Disease Control and Prevention have reported just a little less than 1,600 confirmed flu cases in the US as a result of nearly 1 million tests.
The CDC reports that all 50 states and Puerto Rico have “minimal” trends in flu cases. In fact, less than two dozen new cases have been reported in the past week.
These are similar, almost unheard of trends in Utah.
The Utah Department of Health’s Weekly Influenza Dashboard shows that there have been a total of only 13 hospitalizations due to influenza through February 13. Last year there were a total of 1,310 hospital admissions for influenza.
Pavia said there has been one pediatric hospitalization compared to “several hundred” that would normally happen at this point in the flu season.
There have been so few cases of late that there wasn’t enough data to post the most recent influenza positivity rate. The figures in a chart compared to previous years are astonishing.
It is not known why both viruses essentially disappeared this winter. One theory for the flu is that there were so few cases during the winter in the Southern Hemisphere, and travel restrictions were in place so that the flu couldn’t actually be transmitted from that region of the world, Pavia explained. The other is that masks and other guidelines to prevent the spread of COVID-19 work to stop other respiratory illnesses.
RSV, on the other hand, is “a little more confusing,” Pavia added.
“RSV doesn’t disappear completely every summer. There are cases in warmer climates year round,” he said. “Places like New Orleans and Miami have some RSV year round, so you’d think this would be our reservoir that would seed it and let RSV pop up this winter, but it’s not happening.”
Masking, keeping children at home and keeping babies away from less possible exposure to RSV are theories that could explain its deterioration, according to Pavia. Still, experts have no idea why it’s “practically zero,” not just in Utah, but across the country.
Why RSV and the flu can come back
However, the good news now comes with a caveat. Australian doctors reported similar trends for both influenza and RSV during the winter in the Southern Hemisphere. Then RSV numbers rose sharply just before summer started in the Southern Hemisphere.
Australian Broadcasting Corporation reported last December that RSV cases in all ages have fallen from nearly zero during the winter months of New South Wales. By November, there had been more than 1,600 cases in the month alone.
“It’s very likely that if both the flu and RSV are gone for a while, you’ll have more people who are fully susceptible to it,” Pavia said. “So when it arrives, it spreads more dramatically and we see a more serious disease.”
The reason the flu is coming back more intensely is that influenza is adapting and it is difficult to know which strain of the virus will arrive. The decline in RSV, on the other hand, means that if it arrives later this year or next year, there would be an even larger group of babies who should be fighting it for the first time because they haven’t experienced it now.
“RSV is going to do something really weird when it comes back,” added Pavia. “We really can’t predict it that well. Our gut feeling is that it will come back and we will have a bad RSV year when it comes back.”