(Bloomberg) -- The flu is sending more children to the hospital in the US right now than it has in over a decade, just as an autumn spike in severe RSV cases is starting to recede.

Severe cases of RSV, or respiratory syncytial virus, have overloaded children’s hospitals the past few months. In early November, when cases surged, about 77% of the country’s pediatric hospital beds were filled with patients, according to an analysis of Health and Human Services Department data. The situation has eased a bit, but 73% of those beds remain occupied as other viruses tick up.

Over the past four weeks, positive flu tests reported to the Centers for Disease Control and Prevention by clinical labs have more than doubled. Flu hospitalizations among minors reached 13 per 100,000 children, a high not seen this early in the season since 2009, according to CDC data.

Meanwhile, rates of severe RSV appear to be slowing. Pediatric RSV hospitalizations among children under 18 fell by more than a third for the week ending Nov. 19 compared with the week prior, to about 10.6 per 100,000, according to CDC data. The percentage of RSV tests that turn up positive, a measure of an outbreak’s intensity, is also slowing, figures show. 

Public health officials have been warning of a “tripledemic” with flu, RSV and Covid-19 all circulating simultaneously and earlier in the season than usual. Part of the problem is that kids haven’t been exposed to as many viruses in the past few years because of masking and social distancing so they might not have as much natural immunity to viruses like RSV. But instead of all of these viruses hitting at once, it’s starting to look like hospitals may face wave after wave for the foreseeable future.

“Over the next few weeks, RSV will continue to be a problem, but it’s going to start decreasing and we’ll actually be seeing more flu as a main driver of hospitalizations,” said Michael Chang, a pediatric infectious disease specialist at UTHealth Houston and Children’s Memorial Hermann Hospital. 

RSV is unlikely to peak multiple times during one season, Chang said. “While I believe that we will be past the worst of RSV to avoid a true ‘tripledemic’ during Christmas and New Year, the interplay of flu and SARS-CoV-2 variants remains to be seen.”

Kids ages 4 and under are the second-biggest group of people being sent to the hospital with the flu this year, behind those 65 and older, CDC data show. Twelve children have died of the flu so far this season. Throughout the 2019-2020 flu season, 199 children died of the virus, according to the CDC.

Children’s hospitals in the US have been pushed to their limit on more than one occasion over the past few years. Covid-19 hospitalizations pressured pediatric wards where inpatient units and beds had already been shrinking. Last month, children’s hospitals warned that their emergency rooms were getting swamped with young patients in respiratory distress and some school districts have reported unusually high student absences. 

The US doesn’t yet have an RSV shot for kids, though drugmakers are working on new vaccines that could help stem future surges. Health officials have been encouraging flu shots for kids for two decades but usage isn’t that high: Flu vaccination coverage for kids under 18 this season is about 35%, according to the CDC. As for the new Covid-19 shot, about 12% of kids 5 and under have gotten a booster, data show.

©2022 Bloomberg L.P.