Respiratory syncytial virus, commonly called RSV, is a highly contagious virus that infects the lungs and airways. Nearly every child catches it by age two, and adults can be reinfected throughout their lives. For most people, RSV causes symptoms similar to a common cold. But in infants, older adults, and people with weakened immune systems, it can lead to serious lung infections that require hospitalization.
How RSV Infects the Airways
RSV belongs to the same viral family as parainfluenza, measles, and mumps. It carries its genetic material as a single strand of RNA wrapped in a protective envelope. Two proteins on the virus’s surface do the heavy lifting during infection: one attaches the virus to the cells lining your airways, and the other fuses the virus with those cells so it can slip its genetic material inside. Once inside, the virus hijacks the cell’s machinery to make copies of itself, which then spread to neighboring cells.
There are two subtypes of RSV, called type A and type B, which differ slightly in their surface proteins. Both circulate during RSV season, though type A tends to cause more severe illness. This surface variation is one reason people can catch RSV more than once, since immunity from a previous infection doesn’t fully protect against future strains.
How RSV Spreads
RSV travels through respiratory droplets when an infected person coughs or sneezes near you. Those droplets can land in your eyes, nose, or mouth. Direct contact matters too, particularly kissing a child who has the virus. You can also pick it up from contaminated surfaces like doorknobs, crib rails, or toys, then transfer it to your face before washing your hands.
The virus is surprisingly durable on hard surfaces, surviving for many hours on tables and countertops. On soft surfaces like tissues and hands, it dies off more quickly but can still linger long enough for transmission. This is why frequent handwashing and surface cleaning are especially important during RSV season, which typically runs from fall through spring in the United States.
Symptoms in Infants and Young Children
RSV usually starts with what looks like an ordinary cold: congestion, runny nose, sneezing, and a mild cough. In many children, that’s where it stays. But a few days into the illness, some infants develop lower respiratory tract involvement, meaning the infection moves deeper into the lungs. When this happens, the cough worsens, breathing becomes faster and more labored, and you may notice the skin between or below the ribs pulling inward with each breath. These are signs the child is working harder than normal to get air in.
Wheezing is common as inflamed airways narrow and trap air. Very young infants, particularly those under 12 weeks, may not wheeze at all and instead show more subtle signs like poor feeding, unusual irritability, or pauses in breathing. RSV symptoms tend to peak around days four through six of illness before gradually improving, though the cough can linger for weeks.
Symptoms in Adults
Most healthy adults experience RSV as a standard upper respiratory infection: runny nose, sore throat, headache, fatigue, and a cough that hangs around longer than expected. It’s often mistaken for a cold or even the flu. For adults over 65, though, RSV poses a real threat. During the 2022-2023 season, an estimated 59,000 adults aged 75 and older were hospitalized with RSV in the United States, along with 34,000 adults aged 65 to 74. Nearly 5,550 older adults died from RSV-related illness that season. People with chronic lung conditions like COPD or asthma are especially vulnerable, since RSV can trigger severe flare-ups.
Who Is at Highest Risk
Several factors increase the chance of severe RSV illness. In children, the biggest risk factors are:
- Age under 12 weeks
- Premature birth
- Chronic lung disease, including conditions like bronchopulmonary dysplasia or cystic fibrosis
- Congenital heart disease
- Weakened immune system
- Male sex
- Lack of breastfeeding
- Crowded living conditions
In adults, the risk rises sharply after age 65 and is amplified by chronic heart or lung disease, diabetes, or any condition that suppresses the immune system.
Bronchiolitis and Pneumonia
The two main complications of RSV are bronchiolitis and pneumonia. Bronchiolitis occurs when the smallest airways in the lungs (the bronchioles) become inflamed and clogged with mucus. It’s the most common reason infants are hospitalized with RSV. Doctors diagnose it based on symptoms and a physical exam rather than lab tests or X-rays. The hallmarks are wheezing, a prolonged exhale, and crackling sounds heard through a stethoscope.
Pneumonia develops when the infection reaches the lung tissue itself, causing fluid and inflammation in the air sacs. This is more common in immunocompromised patients, who may not show typical wheezing at all. Instead, their illness can progress rapidly to widespread lung inflammation. In the most severe cases, this can lead to acute respiratory distress syndrome, a life-threatening condition requiring intensive care.
How RSV Is Diagnosed
If your child or an older family member develops concerning respiratory symptoms during RSV season, a healthcare provider can confirm the diagnosis with a test. The gold standard is a molecular test called RT-PCR, which detects the virus’s genetic material with high accuracy. Rapid antigen tests are also available and give results in minutes, but they miss about 25% of true infections. In children under five, rapid tests are even less reliable, catching only about 63% of cases. When the rapid test is positive, it’s almost certainly correct (specificity around 97%), but a negative result doesn’t rule RSV out.
In practice, many mild cases are never formally tested. Testing matters most when results would change treatment decisions, such as in hospitalized infants or older adults with worsening symptoms.
Treatment and Home Care
There is no antiviral medication routinely used to treat RSV. Care is focused on managing symptoms and keeping the body supported while the immune system fights off the virus. For most people, that means:
- Staying hydrated. Dehydration is one of the biggest concerns, especially in infants who may struggle to feed while congested.
- Managing fever and discomfort with acetaminophen or ibuprofen. Aspirin should never be given to children.
- Using saline drops and gentle suctioning to clear nasal congestion in babies.
People with COPD or asthma may need additional treatment for flare-ups triggered by the infection. Hospitalized infants sometimes require supplemental oxygen or, in severe cases, mechanical breathing support. Most children with RSV recover fully within one to two weeks, though the cough often persists longer.
Vaccines and Preventive Options
RSV prevention has changed dramatically in recent years. There are now three FDA-approved vaccines for adults aged 60 and older. Two of those vaccines are also approved for younger adults (age 50 or 18 and up, depending on the product) who have conditions putting them at increased risk for severe RSV.
For infants, protection comes through two routes. Pregnant individuals can receive an RSV vaccine between 32 and 36 weeks of pregnancy, which passes protective antibodies to the baby before birth, shielding them through the first six months of life. Alternatively, infants who didn’t receive that protection before birth can get nirsevimab, an injectable antibody given during RSV season. Real-world data show nirsevimab is at least 70% effective at preventing RSV hospitalization in babies, and clinical trials found roughly 80% efficacy against RSV-related lower respiratory infections requiring hospitalization.
Nirsevimab is recommended for babies under eight months entering their first RSV season if their mother didn’t receive the RSV vaccine during pregnancy, if vaccination status is unknown, or if the baby was born within 14 days of maternal vaccination. Children aged 8 to 19 months with certain high-risk conditions, including chronic lung disease, severe immune deficiency, cystic fibrosis with significant lung involvement, or American Indian and Alaska Native heritage, are recommended to receive it before their second RSV season as well. The ideal timing for any infant RSV protection is October through November, just before RSV season picks up, or within the first week of life for babies born during the season.