For most people, RSV (respiratory syncytial virus) causes nothing worse than a common cold. But for infants, young children, and adults over 65, it can be serious enough to require hospitalization. Globally, RSV causes over 3.6 million hospitalizations and roughly 100,000 deaths in children under 5 each year, with about half of those deaths occurring in babies younger than 6 months.
Mild RSV Looks Like a Cold
The majority of RSV infections stay in the upper airways and produce familiar symptoms: runny nose, cough, sneezing, mild fever, and fatigue. In healthy adults, it often feels like a standard cold and clears up within a week or two without any special treatment. Many adults who catch RSV never realize it’s anything other than a seasonal bug.
In infants and toddlers, RSV typically starts with a runny nose and decreased appetite. A cough develops one to three days later, sometimes followed by sneezing, fever, and wheezing. At this stage, the illness is still manageable at home for most kids.
When RSV Turns Serious
RSV becomes dangerous when it moves from the nose and throat into the smaller airways of the lungs. The virus destroys the tiny hair-like cells that normally sweep mucus out of the airways. As those cells die and slough off, debris accumulates in the narrow bronchioles. At the same time, the airway lining swells and produces excess mucus. The combination of dead cell debris, swelling, and mucus plugs the small airways, trapping air and making it progressively harder to breathe.
This is what doctors call bronchiolitis, and it’s the hallmark of severe RSV in babies. It can also progress to pneumonia. Very young infants may not wheeze or cough much at all. Instead, they may become unusually irritable, lethargic, or stop breathing briefly (a symptom called apnea). These pauses in breathing are one reason RSV is especially dangerous in the first few months of life: the airways are so small that even modest swelling can cause significant obstruction.
Who Faces the Highest Risk
Age is the single biggest risk factor. In the U.S. during the 2024-2025 season, roughly 9 to 11 out of every 1,000 infants under 8 months old were hospitalized for RSV. Rates were similar for children aged 8 to 19 months. Premature babies, infants with congenital heart disease, and children with weakened immune systems face even steeper odds.
On the other end of the age spectrum, an estimated 110,000 to 180,000 adults aged 50 and older are hospitalized for RSV in the U.S. each year. Chronic lung disease, heart failure, kidney disease requiring dialysis, severe obesity, diabetes with organ damage, and conditions that weaken the immune system all raise the risk of a mild RSV infection becoming a life-threatening one. Nursing home residents are particularly vulnerable.
How RSV Compares to Flu and COVID
In a large comparison during the 2023-2024 respiratory season, RSV was actually the mildest of the three major respiratory viruses for adults. The 30-day hospitalization risk for people who tested positive was 14.3% for RSV, compared with 16.2% for COVID-19 and 16.3% for influenza. The 30-day risk of death was similar for RSV and flu (both around 0.7%) and slightly higher for COVID (1.0%). Over six months, COVID carried the highest mortality, while RSV and flu remained comparable.
For infants, though, the picture flips. RSV is the leading cause of hospitalization in babies under one year old, outpacing both flu and COVID in that age group.
Long-Term Effects on Children
Severe RSV in infancy doesn’t just resolve and disappear. Children who catch RSV during their first year of life have a 26% higher risk of developing asthma by age 5 compared to children who avoid the virus. In one study, 21% of children infected with RSV as infants had asthma by age 5, versus 16% of those who hadn’t been infected. Researchers estimate that about 15% of early childhood asthma cases could be prevented if infants avoided RSV infection altogether.
Warning Signs That Need Immediate Attention
If your child is breathing rapidly, pulling in the skin between or below the ribs with each breath, flaring the nostrils, or bobbing the head while breathing, those are signs the body is working hard to get air in. Bluish color around the lips or fingertips signals that oxygen levels have dropped. Any pause in breathing lasting more than a few seconds in a young infant warrants emergency care. Also watch for signs of dehydration: fewer wet diapers, no tears when crying, or refusing to drink.
Prevention Options Available Now
The landscape for RSV prevention has changed substantially. For infants, a single-dose antibody shot is now available and has proven highly effective. In a CDC evaluation from the 2024-2025 season, the shot reduced RSV-related ICU admissions by 80% overall. The protection was strongest in the first two months after the dose (86% effective) and remained meaningful through six months (66% effective). Since its introduction, RSV hospitalization rates among infants under 8 months have dropped by roughly 45 to 52% compared to pre-pandemic seasons.
For older adults, three RSV vaccines are now licensed in the U.S. The CDC recommends a single dose for all adults 75 and older and for adults 50 to 74 who have conditions that raise their risk of severe illness. It’s not an annual shot. One dose completes the series, and the best time to get it is late summer or early fall, before RSV season picks up. In most of the continental U.S., that means August through October.
For the 97% of childhood RSV deaths that occur in low- and middle-income countries with limited access to supportive care, these new tools could eventually make an enormous difference, though availability and distribution remain challenges.