SALT LAKE CITY – Although COVID-19 transmission rates continue to fall, two diseases that normally result in many pediatric hospitalizations remained almost non-existent during the winter.
Respiratory syncytial virus, or RSV, and influenza resulted in virtually no hospitalization at Hospital Infantil Primário. This is a welcome surprise for pediatric specialists who typically handle 80 to 120 hospitalizations for RSV and dozens of intensive care unit admissions per week in addition to hundreds of annual hospitalizations for influenza.
“This is really remarkable,” said Dr. Andrew Pavia, a pediatric infectious disease specialist at Primary Children’s Hospital, during a news conference on Monday about pediatric hospitalization trends for both viruses.
The hospital saw more cases of the rare complication of SARS-CoV-2 called multisystemic inflammatory syndrome in children, or MIS-C, than flu or RSV. It is estimated that about 75 cases of MIS-C have been treated at the hospital in recent months.
RSV is something that affects “virtually all children” in the early years after birth. It usually results in coughing and wheezing; some children end up with shortness of breath and end up needing to be hospitalized.
Adults over 75 also suffer from RSV. Pavia said this ends up resulting in many cases of pneumonia in the elderly. Older children and adults often experience symptoms similar to the cold.
The Primary Children’s Hospital has not yet reported a single hospitalization for RSV during the typical season.
“We are seeing something I have never seen in the past 35 years,” said Pavia. “If you go back to history, it didn’t really happen, except briefly after the 2009 influenza pandemic.”
Then there is the flu, which usually affects hundreds of thousands of Americans every year. So far, the Centers for Disease Control and Prevention have reported just under 1,600 confirmed cases of flu in the United States, 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 were reported in the most recent week.
These trends are almost unheard of in Utah.
The Utah Department of Health’s weekly influenza panel shows that there were only 13 total hospitalizations for influenza as of February 13. There were 1,310 total hospitalizations for influenza last year.
Pavia said there was a pediatric hospitalization, compared to “several hundred” that would normally happen at this point in the flu season.
Lately, there have been so few cases that there is not enough data to post the most recent percent positive for the flu. The numbers on a graph compared to previous years are impressive.
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 that travel restrictions were in place, so the flu could not really 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 prevent other respiratory diseases.
RSV, on the other hand, is “a little more baffling,” added Pavia.
“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 some RSV all year round, so you would think it would be our reservoir that would sow it and make the RSV come out this winter, but it’s not happening.”
Masking, keeping children at home and keeping babies away from the least possible exposure to RSV are theories that, according to Pavia, may explain their decline. Still, experts have no idea why it is “practically zero” not just in Utah, but across the country.
Why RSV and the flu can “roar”
The good news now comes with a caveat, however. Australian doctors have reported similar trends for influenza and RSV during the southern hemisphere winter. Then, RSV numbers increased sharply just before the start of summer in the southern hemisphere.
The 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 more than 1,600 cases in the month alone.
“It is very likely that when both flu and RSV are absent for a while, you will have more people who are totally susceptible to it,” said Pavia. “So when it arrives, it spreads more dramatically and we see more serious illnesses.”
The reason the flu comes back with more intensity is that it adapts 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 will be an even larger group of babies who will have to fight it for the first time because they haven’t tried it now.
“RSV will do something really strange when it comes back,” added Pavia. “We really cannot predict this very well. Our feeling is that he will be back in full force and that we will have a bad RSV year when he returns.”