RSV is extremely common in babies. A U.S. birth cohort study published in Emerging Infectious Diseases found that 53.4% of infants were infected with RSV during their first year of life. By age two, nearly all children have been exposed at least once. For most babies, RSV looks like a bad cold. For a smaller but significant number, it leads to a doctor’s visit, an ER trip, or a hospital stay.
More Than Half of Babies Get RSV Before Age One
In a population-based surveillance study tracking 1,680 healthy, full-term infants in the United States, 897 tested positive for RSV before their first birthday. That’s a 53.4% infection rate in a single year, making RSV one of the most widespread respiratory infections in early childhood. The virus spreads easily through coughs, sneezes, and contaminated surfaces, and it circulates widely enough that avoiding it entirely is difficult.
People don’t develop complete immunity after an RSV infection, so babies can catch it more than once, even within the same season. Each reinfection is typically milder than the first, but repeated bouts are part of why the virus is so pervasive in this age group.
When RSV Season Hits
RSV follows a seasonal pattern in the United States. The season typically begins between mid-September and November, peaks sometime between November and February, and tapers off between early February and May. The exact timing varies by region and year. Babies born just before or during peak months face the highest chance of exposure during the weeks when their immune systems are least prepared.
How Many Babies End Up in the Hospital
While most RSV infections stay mild, the virus is the leading cause of hospitalization in infants. Before newer preventive treatments became available, roughly 15 out of every 1,000 babies under 8 months old were hospitalized for RSV each season, based on pooled CDC surveillance data from 2018 to 2020. That translates to tens of thousands of infant hospitalizations annually across the country.
Beyond hospitalizations, the outpatient burden is enormous. Estimates based on national surveillance data suggest that RSV drives approximately 472,000 emergency department visits and 1.6 million pediatric office visits each year among children under two. That works out to about 60 ER visits and 206 office visits per 1,000 children in that age group annually.
Which Babies Face the Highest Risk
RSV can make any baby sick, but certain groups face a much higher risk of severe illness. The younger the infant, the greater the danger. Babies under six months old have the smallest airways and the least mature immune defenses, which makes them particularly vulnerable to the breathing problems RSV can cause.
Other high-risk groups include:
- Premature babies, whose lungs may not have fully developed before birth
- Babies with chronic lung disease or congenital heart disease
- Children with weakened immune systems
- Children with severe cystic fibrosis
- Children with neuromuscular disorders, particularly those who have difficulty swallowing or clearing mucus
- American Indian and Alaska Native children, who experience higher rates of severe RSV for reasons that likely involve both healthcare access and environmental factors
For healthy, full-term babies without any of these risk factors, RSV usually resolves on its own within one to two weeks. But even in otherwise healthy infants, the virus occasionally causes bronchiolitis (inflammation of the small airways in the lungs) that requires medical attention.
What RSV Looks Like in a Baby
RSV often starts like a regular cold: runny nose, decreased appetite, coughing, sneezing, and mild fever. In many babies, that’s where it stays. The trouble comes when the virus moves deeper into the lungs, which is more likely in very young infants. Signs that RSV is becoming more serious include wheezing, rapid or labored breathing, flaring nostrils, and a visible caving-in of the chest with each breath. Some babies, especially those under three months, may have pauses in breathing or become unusually irritable and lethargic.
Symptoms generally worsen around days three through five of illness before gradually improving. Coughing can linger for a couple of weeks even after the worst has passed.
How New Preventive Treatments Are Changing the Numbers
The landscape shifted significantly starting in the 2024-2025 RSV season with the wider availability of a preventive antibody treatment given to infants. CDC data from that season shows a meaningful drop in hospitalizations: among babies under 8 months, the hospitalization rate fell to 8.5 per 1,000, down from 15.0 per 1,000 in the pre-prevention era. That’s roughly a 43% reduction.
The protective antibody has proven 80% effective at preventing RSV-related ICU admissions and 83% effective against acute respiratory failure in infants during their first RSV season. These numbers come from a CDC evaluation spanning 24 states during the 2024-2025 winter. Protection was strongest in the weeks immediately following administration, with a median of about 50 days between receiving the treatment and the onset of any breakthrough illness.
Maternal vaccination during pregnancy is another option now available, designed to pass protective antibodies to the baby before birth. Together, these tools are expected to continue reducing hospitalizations in coming years, though RSV itself remains just as widespread. The virus still infects the majority of infants. What’s changing is how often those infections become severe enough to require intensive medical care.