BATON ROUGE - Seasonal flu activity is "elevated across the country," with "high" or "very high" respiratory virus activity in more than half of US states, according to an update published Friday by the US Centers for Disease Control and Prevention.

And health care systems nationwide continue to feel the strain of a respiratory virus season that has hit earlier and harder than usual.

There have been about 8 flu hospitalizations for every 100,000 people this season -- rates typically seen in December or January. The cumulative hospitalization rate hasn't been this high at this point in the season in more than a decade, according to the CDC.

In Louisiana, activity involving flu-like illness is at a 5-year-high and is tracking well above the national average.

The RSV hospitalization rate is 10 times higher than usual for this point in the season, too. Children are especially at risk: More than 8 out of every 1,000 infants under 6 months old and 4 out of every 1,000 infants between 6 months and 1 year have been hospitalized with RSV this season, CDC data shows.

This week, the American Academy of Pediatrics and the Children's Hospital Association requested a formal emergency declaration from the federal government to support hospitals and communities amid an "alarming surge of pediatric respiratory illnesses, including respiratory syncytial virus (RSV) and influenza, along with the continuing children's mental health emergency."

"These unprecedented levels of RSV happening with growing flu rates, ongoing high numbers of children in mental health crisis and serious workforce shortages are combining to stretch pediatric care capacity at the hospital and community level to the breaking point. Due to these challenges, pediatric hospitals and pediatricians are being asked to support more care and higher levels of care than ever before," the leaders of the organizations wrote in a letter to President Joe Biden and US Health and Human Services Secretary Xavier Becerra. "We need emergency funding support and flexibilities along the same lines of what was provided to respond to COVID surges."

Pediatric hospitals have been more full than usual in recent months, HHS data shows. More than three-quarters of pediatric hospital beds are in use nationwide, up from an average of about two-thirds over the past two years.

"Hospital systems, medical care facilities, STAT clinics, pediatricians' offices, adult doctors' offices are all feeling the stress of these respiratory viruses right now," Dr. William Schaffner, medical director of the National Foundation for Infectious Diseases and a professor at Vanderbilt University Medical Center, said at a briefing held by the Infectious Diseases Society of America on Friday.

In the state of Washington, emergency rooms are in "crisis mode" and are "bordering, if not already in, disaster mode," Dr. Tony Woodward, medical director of emergency medicine at Seattle Children's Hospital, said this week.

"Our ER is at 100 percent capacity at almost 24 hours a day and in the evening is up to 300 percent capacity, and what that means is, for patients who come for emergencies, [they] aren't treated immediately," Woodward said.

Dr. Rustin Morse, chief medical officer at Nationwide Children's Hospital in Ohio, said Tuesday that it has had to be "judicious" about patients to accept as transfers.

"We are all seeing and being asked to accept patients far away, and we've had requests as far away as Virginia and Missouri," Morse said. "And we've had to say no to those other hospitals in faraway states so that we can optimize our ability to care for patients inside the state of Ohio."

While RSV activity shows signs of slowing in the South, it's still spreading nationwide, with nearly 1 in 5 PCR tests coming back positive. And flu activity continues to be highest in the South. Data from Walgreens tracking prescriptions for antivirals such as Tamiflu suggests hotspots centered in Mississippi, Texas and Louisiana, spreading from Houston and the Gulf Coast area up to Knoxville.

"It's one after the other after the other," Dr. Tina Tan, a pediatrics professor at Northwestern University's Feinberg School of Medicine and vice president of the Infectious Diseases Society of America, said at Friday's briefing. "RSV has already strained the hospital systems to capacity or over capacity. Now you have flu that is starting to surge in other areas where they're trying to deal with the RSV surge, and you also have Covid that's starting to increase. So it really is putting a major strain on hospital systems all across the United States."

The US is in a different place this holiday season than it was in previous pandemic years, Dr. Ashish Jha, the White House Covid-19 response coordinator, told CNN on Thursday.

"I'm hoping we're not to see anything like the spike we saw in January, but we may very well still see a lot more infections in the weeks and months ahead," Jha said. "The good news, though, is that we can gather safely, we can do all of these things, if people go ahead and get that updated bivalent vaccine that's available, get treated if you have infection. We're just in a very different place."

CDC data shows that less than 5% of the US population lives in a county that's considered to have a "high" Covid-19 community level, a measure that captures community transmission and hospital capacity. But for the first time in weeks, CDC forecasts suggest that trends in new Covid-19 hospitalizations will rise in the coming weeks.

While the Covid-19 emergency declaration remains in place, the federal government has not made a formal emergency declaration around children's health care. HHS and the CDC are in regular contact with health care leaders and providers, actively monitoring situational needs and ready to provide assistance on a case-by-case basis, an HHS spokesperson told CNN.

Experts encourage taking preventative measures to stay healthy during this unusual respiratory virus season.

"We've learned some things from Covid. Masks work. Dust them off, bring them back out," Schaffner said.

They also urge all those eligible to get their flu and Covid-19 vaccines, along with other routine vaccinations.

Routine vaccination rates fell during the Covid-19 pandemic and have not improved much. The situation is "pretty bad in the pediatric population, because vaccination rates in some age groups are still 50% less than what they were pre pandemic," Tan said. So there are a lot of unprotected children out there that are at risk for coming down with vaccine preventable diseases."

Children also lag in Covid-19 vaccination rates. Less than 5% of children younger than 5 have completed their initial series, along with less than a third of children ages 5 to 11, according to CDC data.