RSV in Babies: Symptoms, Treatment, and When to Worry

Respiratory syncytial virus (RSV) infects nearly all children by age 2. In older children and adults, it causes symptoms identical to a common cold — a nuisance, nothing more. In babies under 12 months, and especially premature babies and those under 6 months, RSV can cause bronchiolitis, a lower respiratory infection that is the leading cause of infant hospitalization in the United States. Every year, RSV sends approximately 58,000 children under 5 to the hospital. Understanding the progression from "just a cold" to something more serious — and knowing when to act — can be the difference between managing at home and an emergency room visit.

Why Babies Are Vulnerable

The answer comes down to anatomy and immunology. Baby airways are tiny — a newborn's bronchioles (small airways in the lungs) are only about 1 to 2 millimeters in diameter. When RSV causes inflammation and triggers mucus production in these small passages, even minor swelling can significantly restrict airflow. In an adult, the same degree of inflammation might cause a mild cough. In a baby, it can cause clinically significant breathing difficulty.

Premature babies face even higher risk because their airways are smaller, their lungs may not have fully developed, and their immune systems are less mature. They have fewer antibodies passed from their mothers during the last weeks of pregnancy (when the most significant transfer occurs), leaving them less equipped to fight the infection. Babies with congenital heart disease or chronic lung conditions are also at elevated risk for severe RSV illness.

Additionally, babies can't blow their nose or cough effectively to clear the thick, sticky mucus that RSV produces. In adults and older children, coughing and nose-blowing move mucus out of the airways. Babies lack the muscle coordination and force needed for effective clearance, so mucus accumulates in already-tiny airways, progressively worsening the obstruction. This is why suctioning is so important in managing RSV in infants.

Symptom Progression: What to Watch For

RSV follows a characteristic pattern that helps parents anticipate what's coming. Understanding this timeline helps you prepare and know when the situation is changing.

Days 1-3: The Cold Phase

RSV typically starts looking like any ordinary cold: clear runny nose, mild cough, low-grade fever (usually under 101°F), sneezing, and slightly decreased appetite. At this stage, it's genuinely indistinguishable from the dozens of other cold viruses children catch. You might not think anything of it, and for many babies, this is as far as it goes — the cold resolves within a week without complications.

Days 3-5: Potential Escalation

This is the critical window to watch. In some babies, particularly those under 6 months, the virus migrates from the upper respiratory tract (nose and throat) to the lower respiratory tract (bronchioles and lungs). Signs that this is happening include a cough that changes character — becoming wet, persistent, or wheezy rather than dry and intermittent. Breathing rate increases, and you may notice the baby's nostrils flaring with each breath. Visible effort to breathe appears: the skin between the ribs pulls in with each breath (intercostal retractions), the belly pushes out as the baby uses abdominal muscles to help breathe, or the area at the base of the neck sucks in with inhalation (suprasternal retractions).

Feeding difficulty is often one of the earliest practical signs that bronchiolitis is developing — the baby can't breathe and suck simultaneously, so they pull away from the breast or bottle after a few sucks, breathe, and then try to feed again. Feedings become shorter and more frequent, and total intake drops. Increased fussiness or, conversely, unusual lethargy and decreased interest in surroundings are both concerning signs.

Days 5-7: Peak Illness

If bronchiolitis develops, symptoms typically peak around day 5 to 7 before gradually improving. This is important to know because parents often become most alarmed as symptoms worsen and need to understand that the peak doesn't necessarily mean the illness is spinning out of control — it may be following the expected trajectory. The total illness course is usually 1 to 2 weeks, with a lingering cough that can persist for up to 4 weeks. Wheezing may continue for 2 to 3 weeks even after the acute phase resolves.

Related: Croup: The Barking Cough Guide

Home Management for Mild Cases

Many babies with RSV can be safely managed at home with attentive supportive care. The key interventions are maintaining hydration, keeping airways as clear as possible, and monitoring closely for deterioration.

Saline nasal drops (2-3 drops per nostril) followed by gentle bulb suctioning are the most effective tool for clearing nasal mucus. Do this before feedings and before sleep — the improvement in breathing after clearing congested nasal passages can be dramatic. Don't oversuction, which can cause nasal swelling that worsens congestion. Limit suctioning to 3 to 4 times per day unless the baby is visibly struggling.

Offer smaller, more frequent feedings since babies tire quickly when breathing is harder and can't sustain long feeds. For breastfed babies, shorter nursing sessions more often work well. For bottle-fed babies, offer smaller volumes every 2 to 3 hours rather than larger feeds every 3 to 4 hours. A cool-mist humidifier in the baby's room helps loosen mucus and soothe irritated airways. Keep the baby slightly upright when possible — holding them in an upright position helps drainage, and for sleep, a slight elevation of the head of the mattress (achieved by placing a rolled towel under the mattress, not a pillow under the baby) can help.

Critically, there is no medication that treats RSV itself. Antibiotics don't work because RSV is a virus, not bacteria. Over-the-counter cough and cold medicines are not recommended for babies and young children — they're ineffective and potentially dangerous. Bronchodilators (like albuterol, used for asthma) are sometimes tried in the hospital setting but have generally not been shown to be effective for RSV bronchiolitis and are not recommended for routine use. Management is purely supportive: keep airways clear, maintain hydration, and let the immune system fight the virus.

When to Go to the ER

Seek emergency care immediately if the breathing rate exceeds 60 breaths per minute (count for a full 60 seconds while the baby is calm — normal rate for infants is 30-60 per minute). If you see retractions — skin visibly pulling in between or below the ribs, above the collarbones, or at the base of the neck with each breath — this indicates significant respiratory effort. If lips, fingernails, or the area around the mouth looks blue or gray (cyanosis), this indicates inadequate oxygenation and is an emergency. If the baby pauses breathing for more than 10 to 15 seconds (apnea), if they refuse to eat or drink entirely, if they have fewer than 4 wet diapers in 24 hours (indicating dehydration), or if they're unusually lethargic, limp, or difficult to wake.

Babies under 3 months with any RSV symptoms should be evaluated by a pediatrician promptly even if symptoms currently seem mild, because young infants can deteriorate from mild to severe more rapidly than older babies. The younger the baby, the lower the threshold should be for seeking medical evaluation.

What Happens at the Hospital

If your baby is hospitalized for RSV, treatment focuses on oxygen support and hydration. Supplemental oxygen is provided through nasal cannula or, in more severe cases, high-flow nasal cannula or CPAP. Deep nasal suctioning may be performed by respiratory therapists. If the baby can't maintain adequate oral intake, IV fluids prevent dehydration. The typical hospitalization for RSV bronchiolitis is 2 to 5 days, with discharge when the baby can maintain adequate oxygen levels on room air and is feeding well enough to stay hydrated.

Prevention

Prevention strategies have improved significantly in recent years. Nirsevimab (Beyfortus) is a monoclonal antibody immunization now recommended for all infants entering their first RSV season. Unlike a traditional vaccine, nirsevimab provides passive immunity through a single injection, offering protection that lasts approximately 5 months through the RSV season. Clinical trials showed it reduced RSV-related hospitalizations by approximately 80 percent. This is a significant advance over the older palivizumab (Synagis), which required monthly injections and was only available to high-risk infants.

An RSV vaccine for pregnant women (Abrysvo) is also available, given during weeks 32 to 36 of pregnancy to pass protective antibodies to the baby before birth. Discuss both options with your obstetrician and pediatrician to determine which approach is best for your family. Beyond immunization, basic hygiene remains important: thorough hand washing before touching babies, limiting exposure to crowds and sick contacts during peak RSV season (fall through early spring in most of the U.S.), keeping sick older siblings away from the baby when possible, and asking visitors not to kiss the baby's face, hands, or anywhere near their mouth during RSV season.