Respiratory syncytial virus is the leading cause of lower respiratory tract infection and infant hospitalization in the United States, accounting for roughly 58,000 to 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 a small percentage of infected babies. The approval of nirsevimab (Beyfortus) and the maternal RSV vaccine (Abrysvo) changed the prevention landscape substantially, and recent seasons produced clear reductions in RSV hospitalizations among protected infants. This guide is educational and does not replace advice from your child’s pediatrician; specific immunization recommendations are set by the CDC/ACIP and the American Academy of Pediatrics (AAP) and can change, so confirm the current schedule with your clinician.
What RSV Is
RSV is a common respiratory virus that nearly all children encounter by age 2. In older children and adults, RSV usually 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, one of the most common reasons infants are admitted to U.S. hospitals.
The virus spreads via respiratory droplets, contaminated surfaces (it can survive several hours on hard surfaces), and direct contact. Per the CDC RSV resource, RSV season historically runs roughly October through March in most of the continental U.S., though post-pandemic seasonality has been less predictable and some regions (such as Florida and parts of the tropics) differ. Because the timing shifts year to year, prevention decisions are usually keyed to the start of your local RSV season.
Symptoms
Early RSV looks like a head cold: runny nose, congestion, mild cough, low-grade fever, and reduced feeding. By day 3 to 5, lower airway symptoms may appear: a more frequent and harsher cough, wheezing, fast breathing (tachypnea), retractions (skin pulling in between and below the ribs and at the notch above the breastbone), nasal flaring, and significant feeding difficulty because the baby cannot breathe and feed at the same time. The AAP notes that symptoms typically peak around days 3 to 5 and can last one to two weeks.
In very young infants and preemies, the first sign of severe RSV may be apnea — pauses in breathing — without much respiratory distress beforehand. This is why the threshold for evaluating young infants with RSV is lower than for older children. If your baby is under about 3 months, err on the side of calling the pediatrician sooner rather than later.
Diagnosis
Diagnosis is usually clinical. RSV-specific testing (rapid antigen or PCR from a nasal swab) is done when the result 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 counting of the respiratory rate, and observation of the 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, because they rarely change care and can lead to unnecessary antibiotics.
Treatment
RSV bronchiolitis is treated with supportive care, and most cases are mild and managed at home. The 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 for typical bronchiolitis. What does help: nasal saline drops with gentle bulb or nasal-aspirator suctioning before feeds and sleep, frequent small feeds to maintain hydration, a cool-mist humidifier, fever control with weight-based acetaminophen or ibuprofen (ibuprofen only in infants 6 months and older, and only as directed by your pediatrician), and close monitoring for worsening. Never give aspirin to a child, and do not give over-the-counter cough and cold medicines to young children.
Hospitalized infants receive supplemental oxygen if they are hypoxic, IV or nasogastric (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 select severely immunocompromised children. Most hospitalized infants stay about 2 to 5 days. There is no antibiotic that treats RSV itself, because RSV is a virus; antibiotics are used only if a bacterial complication (such as an ear infection or pneumonia) develops.
Prevention: The Newer Game-Changers
Two newer prevention tools have substantially changed RSV outcomes, and both work by giving the baby protective antibodies. Because eligibility and timing are set by the CDC/ACIP and AAP and can be updated between seasons, treat the details below as a general framework and confirm the current recommendation with your pediatrician or obstetrician.
Nirsevimab (Beyfortus) is a long-acting monoclonal antibody given as a single intramuscular injection. The CDC recommends nirsevimab for infants under 8 months entering their first RSV season and for certain high-risk children 8 to 19 months entering their second RSV season, unless the mother received the maternal RSV vaccine during pregnancy. CDC data have shown nirsevimab is roughly 80 to 90% effective against RSV-associated hospitalization in the months after the dose. A newer infant monoclonal antibody, clesrovimab (Enflonsia), has also been introduced as an additional option in some settings — ask your pediatrician which product is available and recommended for your baby this season.
The maternal RSV vaccine (Abrysvo) is given to pregnant women, generally between 32 and 36 weeks of pregnancy during RSV season, providing antibody protection that crosses the placenta to the baby for the first months of life. The CDC notes the maternal vaccine reduces the risk of RSV hospitalization in young infants by roughly half. In most cases, either nirsevimab for the infant or the maternal vaccine for the mother is recommended — generally not both — and the decision is made between the family and the obstetric and pediatric teams.
Palivizumab, the older monthly RSV antibody injection, is now reserved for select high-risk infants (very preterm babies, certain congenital heart or lung disease) who cannot get nirsevimab. Keeping routine immunizations current also helps reduce co-infections that can complicate RSV.
RSV Prevention Options at a Glance
| Option | Who it is for | How it is given |
|---|---|---|
| Nirsevimab (Beyfortus) | Infants under 8 months in first RSV season; some high-risk 8-19 months | Single injection to the baby |
| Clesrovimab (Enflonsia) | Newer infant antibody option in some settings | Single injection to the baby |
| Maternal RSV vaccine (Abrysvo) | Pregnant women, usually 32-36 weeks in RSV season | Vaccine to the mother |
| Palivizumab | Select very high-risk infants who cannot get nirsevimab | Monthly injection during season |
This table is a general overview, not medical advice. Which option fits your baby depends on age, risk factors, whether you were vaccinated in pregnancy, and current CDC/AAP guidance — decide with your clinician.
Other prevention basics still matter: hand hygiene, avoiding tobacco smoke exposure, breastfeeding when possible, limiting a newborn’s exposure to crowds and sick contacts during RSV season, and keeping older siblings home from daycare or school when they are ill.
Risk Factors for Severe RSV
The infants most likely to develop severe RSV bronchiolitis include those under about 12 weeks old at the time of infection, premature infants (especially those born under 35 weeks), infants with chronic lung disease of prematurity, infants with hemodynamically significant congenital heart disease, infants with neuromuscular disorders, and infants with immune deficiencies. Exposure to tobacco smoke increases severity. Daycare attendance and the presence of older siblings are major risk factors for any RSV exposure in the first place.
When to Call the Pediatrician — and When to Go to the ER
Call your pediatrician for any infant with a worsening cough, wheezing, fast breathing, decreased feeding (less than half the normal volume, or fewer than 3 to 4 wet diapers in 24 hours), or a 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); fast or clearly labored breathing; severe retractions (the chest or the skin between the ribs caving in) or head bobbing and grunting with each breath; nasal flaring with obvious effort; bluish, gray, or very pale color around the lips, mouth, tongue, or fingertips; severe difficulty feeding to the point of dehydration (no wet diaper for 8 or more hours, no tears, a sunken soft spot, very dry mouth); extreme sleepiness, limpness, or difficulty waking; or any infant under 3 months with a rectal temperature of 100.4°F (38°C) or higher. Trust your instincts — if your baby looks like they are struggling to breathe, get help right away.
Long-Term Effects
Most infants recover from RSV bronchiolitis fully within 1 to 2 weeks, though the cough can linger a bit longer. Some research links severe RSV bronchiolitis in infancy to an increased risk of childhood asthma and recurrent wheezing in the toddler and preschool years, though whether RSV causes this or simply flags children who were already predisposed is still debated. Hospitalization for RSV does not generally cause long-term lung damage in otherwise healthy, full-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. You cannot reliably tell RSV apart from other cold viruses at home, which is why watching how your baby is breathing and feeding matters more than the exact virus name.
Should my baby get nirsevimab?
The CDC recommends nirsevimab for infants under 8 months entering their first RSV season unless the mother received Abrysvo during pregnancy. It is generally covered as a preventive benefit and is included in the federal Vaccines for Children program for eligible children. Because recommendations and available products can change between seasons, discuss timing and the right option for your baby with your pediatrician.
How long is RSV contagious?
Most healthy infants and children shed RSV for about 3 to 8 days, but young infants and immunocompromised children can shed it for up to 3 to 4 weeks. Hand hygiene and avoiding sick contacts during the contagious period help reduce spread within the household.
Can my child get RSV more than once?
Yes. Immunity after RSV is incomplete, and reinfection throughout life is common. Reinfections in older children and adults are usually milder, though older adults and people with heart or lung disease can get severely ill, much like infants.
My baby got the maternal vaccine benefit — does she still need nirsevimab?
Usually not. In most cases babies are protected by either the maternal RSV vaccine in pregnancy or nirsevimab after birth, not both. There are exceptions for some high-risk situations, so confirm with your pediatrician.
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 are worth discussing with your obstetric and pediatric teams ahead of every RSV season. Watch for fast or labored breathing, retractions, feeding difficulty, bluish color, and apnea — those are the signs that move RSV from a manageable home illness to an ER trip. Most infants who get RSV recover fully, often as one of the routine pediatric viral illnesses alongside croup and ear infections.
Quick summary: RSV is a common virus that usually causes a cold but can cause bronchiolitis and breathing trouble in babies. Most cases are mild and treated with supportive care at home. Seek emergency care (call 911) for fast or labored breathing, chest retractions, bluish or gray lips, severe dehydration, or pauses in breathing. Ask your pediatrician about prevention with nirsevimab (Beyfortus) or the maternal RSV vaccine (Abrysvo); recommendations are set by the CDC/ACIP and AAP and can change. This article is educational and is not a substitute for care from your child’s pediatrician.
Sources
- CDC — RSV (Respiratory Syncytial Virus): cdc.gov/rsv
- CDC — RSV Immunizations to Protect Infants (nirsevimab and maternal vaccine): cdc.gov/rsv/vaccines
- American Academy of Pediatrics, HealthyChildren.org — RSV: When It’s More Than Just a Cold: healthychildren.org
- AAP Clinical Practice Guideline: The Diagnosis, Management, and Prevention of Bronchiolitis: publications.aap.org