Respiratory syncytial virus is the leading cause of lower respiratory tract infection and infant hospitalization in the United States, accounting for approximately 58,000-80,000 hospitalizations in children under 5 each year per CDC surveillance. RSV in infants looks like a cold for the first day or two, then can progress quickly to bronchiolitis — wheezing, fast breathing, and feeding difficulty — that becomes serious enough to require hospitalization in roughly 2-3% of infected babies. The 2023 approval of nirsevimab (Beyfortus) and the maternal RSV vaccine (Abrysvo) changed the prevention landscape substantially, and the 2024-2025 season produced clear reductions in RSV hospitalizations among protected infants.
What RSV Is
RSV is a common respiratory virus that nearly all children encounter by age 2. In older children and adults, RSV causes a typical cold. In infants — especially those under 6 months, premature infants, and those with chronic heart or lung disease — RSV can infect the small airways (bronchioles) and cause bronchiolitis, the most common reason infants are admitted to U.S. hospitals.
The virus spreads via respiratory droplets, contaminated surfaces (it survives several hours on hard surfaces), and direct contact. Per the CDC RSV resource, RSV season historically runs October through March in most of the U.S., though post-pandemic seasonality has been less predictable.
Symptoms
Early RSV looks like a head cold: runny nose, congestion, mild cough, low-grade fever, and reduced feeding. By day 3-5, lower airway symptoms appear: more frequent and harsher cough, wheezing, fast breathing (tachypnea), retractions (skin pulling in between and below the ribs and at the suprasternal notch), nasal flaring, and significant feeding difficulty as the baby cannot breathe and feed simultaneously.
In very young infants and preemies, the first sign of severe RSV may be apnea — pauses in breathing — without significant respiratory distress beforehand. This is why the threshold for evaluating young infants with RSV is lower than for older children.
Diagnosis
Diagnosis is usually clinical. RSV-specific testing (rapid antigen or PCR from a nasal swab) is done when results would change management — in hospitalized infants, immunocompromised children, or for cohorting in healthcare settings. Routine outpatient RSV testing is generally not needed because treatment is supportive regardless of which respiratory virus is responsible.
Pulse oximetry to measure oxygen saturation, careful respiratory rate counting, and observation of work of breathing are the most informative parts of the assessment. Chest X-rays are not routinely done in uncomplicated bronchiolitis per the AAP bronchiolitis guideline.
Treatment
RSV bronchiolitis is treated with supportive care. The 2014 AAP bronchiolitis clinical practice guideline emphasizes what does not help: bronchodilators (albuterol), inhaled or systemic steroids, antibiotics, chest physiotherapy, and routine racemic epinephrine in the outpatient setting all lack benefit. What does help: nasal saline drops with bulb suctioning before feeds and sleep, frequent small feeds to maintain hydration, fever control with weight-based acetaminophen or ibuprofen, and close monitoring for worsening.
Hospitalized infants receive supplemental oxygen if they are hypoxic, IV or NG fluids if they cannot maintain hydration, high-flow nasal cannula or non-invasive ventilation for moderate distress, and rarely intubation for severe respiratory failure. The antiviral ribavirin is reserved for severely immunocompromised children. Most hospitalized infants stay 2-5 days.
Prevention: The 2023 Game-Changers
Two newer prevention tools have substantially changed RSV outcomes. Nirsevimab (Beyfortus) is a long-acting monoclonal antibody given as a single intramuscular injection. The CDC recommends nirsevimab for all infants under 8 months entering their first RSV season and for high-risk children 8-19 months entering their second RSV season, unless the mother received the maternal RSV vaccine during pregnancy. CDC surveillance from the 2023-2024 season showed nirsevimab was about 90% effective against RSV-associated hospitalization.
The maternal RSV vaccine (Abrysvo) is given to pregnant women between 32 and 36 weeks gestation during RSV season, providing transplacental antibody protection for the infant in the first months of life. Either nirsevimab to the infant or the maternal vaccine to the mother is recommended — generally not both — and decisions are made between the family and obstetric/pediatric clinicians.
Palivizumab, the older monthly RSV antibody injection, is now reserved for select high-risk infants (very preterm, certain congenital heart or lung disease) who cannot get nirsevimab. Routine immunizations should also be kept current to reduce co-infections.
Other prevention basics: hand hygiene, avoiding tobacco smoke exposure, breastfeeding when possible, limiting exposure of newborns to crowds and sick contacts during RSV season, and keeping older siblings home from daycare or school when ill.
Risk Factors for Severe RSV
The infants most likely to develop severe RSV bronchiolitis include: those under 12 weeks old at infection, premature infants (especially under 35 weeks), infants with chronic lung disease of prematurity, infants with hemodynamically significant congenital heart disease, infants with neuromuscular disorders, infants with immune deficiencies, and infants exposed to tobacco smoke. Daycare attendance and the presence of older siblings are major risk factors for any RSV exposure.
When to Call the Pediatrician — and When to Go to the ER
Call your pediatrician for any infant with worsening cough, wheezing, fast breathing, decreased feeding (less than half normal volume or fewer than 3-4 wet diapers in 24 hours), or fever lasting more than 3 days. Same-day evaluation is appropriate, especially for infants under 3 months.
When to seek emergency care: Call 911 or go to the nearest emergency room if your infant has any of the following: pauses in breathing (apnea) lasting more than 10-15 seconds, blue or gray color around the lips, mouth, or fingertips, severe retractions, nodding/grunting with each breath, severe difficulty feeding to the point of dehydration (no wet diaper for 8+ hours, no tears, sunken fontanelle, very dry mouth), lethargy or extreme floppiness, or any infant under 3 months with a rectal temperature of 100.4°F or higher.
Long-Term Effects
Most infants recover from RSV bronchiolitis fully within 1-2 weeks. Some research links severe RSV bronchiolitis in infancy to increased risk of childhood asthma and recurrent wheezing in the toddler and preschool years, though causality is debated. Hospitalization for RSV does not generally cause long-term lung damage in healthy term infants.
Frequently Asked Questions
How is RSV different from a regular cold?
RSV often starts as a cold, but in infants and young children it can progress to lower airway involvement (bronchiolitis) with wheezing, fast breathing, and feeding difficulty. Older children and adults usually experience RSV as a typical cold without lower airway symptoms.
Should my baby get nirsevimab?
The CDC recommends nirsevimab for all infants under 8 months entering their first RSV season unless the mother received Abrysvo during pregnancy. Insurance covers it through the ACA preventive benefit, and it is included in the federal Vaccines for Children program. Discuss timing with your pediatrician.
How long is RSV contagious?
Most healthy infants and children shed RSV for 3-8 days. Young infants and immunocompromised children can shed for 3-4 weeks. Hand hygiene and avoiding sick contacts during the contagious period reduce spread.
Can my child get RSV more than once?
Yes. RSV immunity is incomplete, and reinfection through life is common. Reinfections in older children and adults are typically milder, though older adults are at increased risk for severe RSV like infants are.
The Bottom Line on RSV in Infants
RSV in infants ranges from a head cold to a hospitalization, with severity strongly tied to age and underlying conditions. Nirsevimab and the maternal RSV vaccine have substantially reduced infant RSV hospitalizations and should be discussed with your obstetric and pediatric teams ahead of every RSV season. Watch for fast breathing, retractions, feeding difficulty, and apnea — those are the symptoms that move RSV from manageable home illness to ER trip. Most infants who get RSV recover fully, often as part of routine pediatric viral illnesses alongside croup and ear infections.