WYNNEWOOD, Pennsylvania (WPVI) -- The number of children currently in the hospital is the highest its been in two years. The culprit? Respiratory syncytial virus, also known as RSV.
"In our hospital, we're seeing the types of numbers we would normally see in the middle of a pretty bad winter," said Dr. Jonathan Miller, chief of primary care with Nemours Children's Health.
RSV is a common virus affecting the respiratory tract, causing cold-like symptoms in adults. But in infants and young children, it can lead to symptoms like labored breathing and even pneumonia. The pandemic upended children's exposure to the virus, thus contributing to the current explosion in hospitalizations.
"I think what we're seeing now is a lot of kids didn't get exposed to RSV for the first year of the pandemic and a lot of adults didn't either, and so the sort of general immunity that people have towards this virus is less than it had been," said Dr. Miller.
Hospitals in at least 43 states plus D.C. have now told ABC News they are grappling with the early surge in pediatric respiratory illnesses.
The Department of Health and Human Services reports out of Delaware's 245 pediatric beds, 89% are currently in use. Pennsylvania's pediatric hospitalization capacity is 79% percent consumed, while New Jersey is using 65% of its pediatric beds.
"We're seeing a lot of RSV right now," said Dr. Ashish Jha, White House COVID-19 Response Coordinator. "My hope is that turns around. What worries me is if we then add in influenza and COVID on top of that, that's where we can get into trouble."
And as we head towards winter, doctors warn of a surge in COVID, flu and RSV cases.
"The problem is as we get a lot of cases of RSV, and it's normal for us to have surges of RSV, it increases the number of people admitted to our hospitals. And they're only there for a couple days, but when you have that on top of flu at the same time, where people are also going to get admitted, and on top of that COVID where people are admitted, it can cause our hospitals to get busier and busier," said Dr. Jon Stallkamp, Chief Medical Officer of Main Line Health.
Health officials say there is no vaccine for RSV, but there are vaccines for the flu and COVID. They recommend getting your vaccines.