SALT LAKE CITY – While COVID-19 transmission rates continue to fall, two diseases that typically result in many pediatric hospitalizations have remained virtually non-existent throughout the winter.
Respiratory syncytial virus (RSV) and influenza have resulted in virtually no hospitalizations in Children’s Primary Hospital. This is a welcome surprise for pediatric specialists who typically care for 80 to 120 RSV hospitalizations and dozens of intensive care stays a week in addition to hundreds of annual hospitalizations for flu.
“That’s really remarkable,” Dr. Andrew Pavia, a pediatric infectious disease specialist at Children’s Primary Hospital, during a press session Monday on pediatric hospitalization trends for the two 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 the flu or RSV. An estimated 75 cases of MIS-C have been treated in the hospital in recent months.
RSV is something that affects “virtually every child” in its first two years after birth. It usually results in coughing and wheezing; some children end up having difficulty breathing and need to be hospitalized.
Adults over the age of 75 also suffer from RSV. Pavia said it ends up leading to many cases of elderly pneumonia. Older children and adults often experience cold-like symptoms.
The Primary Children’s Hospital has not yet reported an RSV hospitalization during the regular season.
“We’re seeing something I’ve never seen in the last 35 years,” Pavia said. “If you go back in history, it really didn’t happen except briefly after the 2009 flu pandemic.”
Then there is the flu, which often affects hundreds of thousands of Americans each year. To date, the Centers for Disease Control and Prevention has only reported just under 1,600 confirmed cases of total flu in the United States as a result of more than one million tests.
The CDC reports that all 50 states and Puerto Rico have “minimal” flu case trends. In fact, less than two dozen new cases were reported in the most recent week.
These are similar trends almost unheard of in Utah.
The Utah Department of Health’s weekly flu scorecard shows that there were only 13 total hospitalizations due to the flu as of Feb. 13. Last year, 1,310 hospitalizations for influenza were recorded.
Pavia said there has been a pediatric hospitalization compared to “several hundred” that would normally happen at this time of the flu season.
Lately, there have been so few cases that there has not been enough data to publish the most recent flu positive percentage. The figures on a graph compared to previous years are staggering.
It is unknown why the two viruses have essentially disappeared this winter. One theory of the flu is that there were so few cases during the winter in the southern hemisphere and that there were travel restrictions, so the flu could not be transmitted from this 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 baffling,” Pavia added.
“The RSV does not disappear completely every summer. There are cases in warmer climates throughout the year,” he said. “Places like New Orleans and Miami have RSV all year round, so you’d think this would be our reservoir that would sow it and make RSV appear this winter, but it’s not happening.”
Masking, keeping children at home, and having babies away from less possible exposures to VSS are theories Pavia said could explain their decline. Still, experts have no idea why it’s “virtually zero” not just in Utah, but across the country.
Why RSV and flu could “roar” again
Now, the good news comes with a warning. Australian doctors reported similar trends for both influenza and RSV during the winter in the southern hemisphere. RSV numbers then rose sharply just before the start of the southern hemisphere summer.
Australian Broadcasting Corporation reported last December that RSV cases at all ages went from almost zero during the winter months in New South Wales. In November, there were only more than 1,600 cases a month.
“It’s very likely that both the flu and RSV are absent for a while, you have more people totally susceptible to the disease,” Pavia said. “So when it arrives, it spreads more dramatically and we see more serious diseases.”
The reason the flu gets fiercer is that the flu is adapting and it’s hard to know which strain of the virus will arrive. The decline of RSV, on the other hand, means that if it comes to the end of this year or next year, there would be an even larger group of children who would have to fight it for the first time because they did not experience it now.
“RSV will do something really weird when he comes back,” Pavia added. “We really can’t predict it very well. Our gut feeling is that it’s going to roar again and we’re going to have a bad RSV year when he comes back.”