This fall is a busy season for pediatricians and hospitals in a growing number of states because an unusually high number of kids have an infection called respiratory syncytial virus -- RSV for short – just as flu cases also spike. Plus, the not-done-yet Covid pandemic remains a concern. After two years of masking in schools and distancing, children have fewer biological defenses to fend off multiple viruses at once. "We may have a tridemic," warns Dr. William Schaffner, an infectious disease specialist at Vanderbilt University School of Medicine in Nashville, Tenn. At St. Jude's Children's Research Hospital in Memphis, Dr. Diego Hijano says: “It's going to be a rough winter.” And at Baystate Children's Hospital in Springfield, Mass., the chief pediatrician comments: "We're really having a capacity problem like I've never seen before."

RSV typically causes mild, cold-like symptoms in adults but can lead to pneumonia and bronchiolitis in very young patients. The elderly also face an elevated risk from the lung infection, which can cause a mucus buildup and make it difficult to breathe. Symptoms are fever, a runny nose, a cough and breathing difficulty – similar to the effects of flu and Covid. Nearly three-quarters of pediatric hospital beds are occupied, according to federal data. "The children's hospitals in this country are drowning right now," says Dr. Elizabeth Mack, head of the pediatric critical-care unit at the Medical University of South Carolina. A hospital in Fort Worth, Texas, is treating about 300 young RSV patients a day.

Unlike with measles or mumps, people can get RSV more than once. Researchers have tried for half a century to develop a vaccine. Because none exists yet, health experts are renewing pleas for people to get vaccinated for influenza and coronavirus. "If people went out there and got their vaccines, we could really get through this without getting into a lot of trouble," White House health adviser Dr. Ashish Jha said last week.

Pediatrician says: "Last year, more people were wearing face masks and children were more likely to stay home while sick. This year, children who haven't been previously exposed to respiratory viruses are getting sick." -- Dr. Laura Romano, Cook Children's Hospital in Fort Worth

White House official says: "It’s concerning – we have three respiratory viruses rising at the same time." – Dr. Ashish Jha, presidential Covid coordinator

RSV impact: The lung virus causes about 14,000 deaths among adults 65 and older and up to 300 deaths among children under 5 each year.