RSV, or respiratory syncytial virus, is one of the most common respiratory infections in young children. It infects cells along the entire respiratory tract, from the nose down to the lungs, and nearly every child catches it by age two. For most kids, RSV looks like an ordinary cold. But in infants and children with certain risk factors, it can progress to serious breathing problems that require hospitalization.
How RSV Affects the Airways
RSV is an RNA virus that specifically targets human respiratory cells. When a child breathes in the virus, it begins replicating in the lining of the nose and throat. In mild cases, the infection stays in the upper airways and resolves on its own. In more severe cases, the virus moves deeper into the lungs, inflaming the small airways (bronchioles) and causing a condition called bronchiolitis. It can also cause pneumonia. The inflammation and mucus buildup in these tiny passages is what makes breathing difficult, especially for infants whose airways are already very small.
How It Spreads
RSV spreads through respiratory droplets when an infected person coughs or sneezes, and through direct contact with contaminated surfaces. The virus can survive for many hours on hard surfaces like tables and crib rails, though it dies more quickly on soft surfaces like tissues and skin. An infected person is typically contagious for 3 to 8 days and may start spreading the virus a day or two before symptoms appear, which makes it difficult to contain in daycare settings and households with multiple children.
RSV season in the continental United States generally runs from fall through spring, with most cases peaking between October and March.
Symptoms and How They Progress
RSV often starts mild and worsens over several days. Early symptoms look like a common cold: runny nose, cough, and reduced appetite. The concern is what comes next. The cough can progress to wheezing or visible difficulty breathing, with the chest pulling inward (retractions) as the child works harder to get air. When a child’s breathing rate climbs above 60 to 70 breaths per minute, feeding often becomes difficult, particularly if nasal congestion is heavy. This combination of poor feeding and labored breathing is what sends many children to the emergency room.
Babies younger than six months can look different from older children with RSV. They may not develop a fever at all. Instead, the warning signs are more subtle: irritability, decreased activity, eating or drinking less than usual, and apnea, which means pauses in breathing lasting more than 10 seconds. These pauses can be alarming, and they’re one reason very young infants with RSV are watched closely.
Which Children Are Most at Risk
Age is the single biggest risk factor. Infants under six months are the most vulnerable because their airways are narrow and their immune systems are still developing. Before the introduction of preventive treatments, RSV hospitalization rates among babies under eight months ran around 15 per 1,000 children per season.
Beyond age, children born prematurely, those with chronic lung disease, and those with congenital heart defects face higher odds of severe illness. Children with weakened immune systems or neuromuscular conditions that affect their ability to cough and clear mucus are also at increased risk.
When RSV Requires Hospitalization
Most healthy infants and young children with RSV recover at home without medical intervention. Hospitalization becomes necessary when a child can’t maintain adequate oxygen levels or can’t take in enough fluids. Doctors assess severity by watching the breathing rate, looking for retractions (the skin pulling in between or below the ribs), and checking oxygen saturation. One study found that when a child’s food intake dropped below 50% of normal over 24 hours, oxygen levels were often lower than expected as well.
Children who are hospitalized typically receive supportive care: supplemental oxygen if saturation drops too low, fluids to prevent dehydration, and in severe cases, mechanical breathing support. There is no antiviral medication that treats RSV. Most hospitalized children improve within a few days and go home once they can breathe comfortably and feed well on their own.
Home Care for Mild RSV
For the majority of children who manage RSV at home, the goal is comfort and hydration. Keeping the nose clear with saline drops and gentle suctioning helps younger babies breathe and feed more easily. Offering smaller, more frequent feedings can help a child who tires quickly during meals. A cool-mist humidifier may ease congestion. Over-the-counter cold medications are not recommended for young children, and antibiotics don’t work against viruses.
The illness typically lasts one to two weeks. The cough can linger after other symptoms have cleared. If breathing worsens at any point, particularly if you notice rapid breathing, flaring nostrils, or a bluish tint to the lips or fingernails, that warrants immediate medical attention.
How RSV Is Diagnosed
Doctors can test for RSV using a nasal swab. The two main types of tests are molecular tests (which detect the virus’s genetic material and are highly sensitive) and antigen tests (which are less sensitive but return results faster). In many cases, especially during peak RSV season, a doctor may diagnose RSV based on symptoms and a physical exam alone, reserving testing for situations where the result would change how the child is managed.
Prevention: RSV Immunizations for Infants
A major shift in RSV prevention arrived with nirsevimab, an antibody given as an injection that provides protection against severe RSV disease. It’s not a traditional vaccine but rather a dose of lab-made antibodies that help an infant’s body fight the virus. The CDC recommends it for all infants younger than eight months who are born during or entering their first RSV season. For children aged 8 through 19 months who are at increased risk for severe disease, a higher dose is recommended before their second RSV season.
The timing matters. For babies born between October and March, the injection should ideally be given within the first week of life, during the birth hospitalization. For babies born outside that window, the best time is shortly before RSV season begins, typically in October or November. Children 20 months and older are not candidates for this treatment, as their risk of severe RSV has dropped significantly by that age.
Early data suggest these preventive measures are working. CDC surveillance from the 2024-25 season found RSV hospitalization rates among infants under eight months dropped to 8.5 per 1,000 compared to 15.0 per 1,000 in the pre-prevention era, a reduction of roughly 43 to 52% depending on the surveillance network. The largest reductions were seen in the youngest infants, those under three months old, where hospitalization rates fell by as much as 71% in some areas.
Long-Term Effects of Severe RSV
For most children, RSV resolves completely. But severe RSV that reaches the lower airways in early life has been consistently linked to recurrent wheezing and a higher risk of developing asthma later in childhood. This doesn’t mean RSV causes asthma outright. The relationship is complex and influenced by a child’s genetics, the specific strain of the virus, and environmental factors like exposure to allergens or tobacco smoke. Still, children who were hospitalized with RSV bronchiolitis as infants are more likely to wheeze with subsequent respiratory infections in the years that follow, and some go on to receive an asthma diagnosis. Researchers continue to untangle whether RSV directly damages developing airways or whether children who get the sickest were already predisposed to airway problems.