Respiratory syncytial virus, better known as RSV, is one of the most common respiratory viruses in the world — and one of the least recognised by name. Almost every child catches it before their second birthday, and adults can catch it again and again. For most healthy adults it feels like an ordinary cold, but for babies under one year old, and for older adults, it can turn into a serious lung infection.
This guide explains what RSV is, how to recognise it, how it spreads, who is most at risk, and what prevention is available in 2026, using CDC guidance. It is general information, not medical advice.
What is RSV?
RSV stands for respiratory syncytial virus. It infects the nose, throat and lungs and causes seasonal epidemics, typically from fall through spring. In the United States, it is the most common cause of bronchiolitis — inflammation of the small airways in the lungs — and pneumonia in children under one year of age.
Most people have had RSV by age two, according to the CDC, but immunity does not last, and repeat infections in healthy adults are usually milder. The virus matters most at the two ends of life: very young babies, whose airways are tiny, and older adults, especially those who are frail or living with chronic heart or lung disease. Our comparison guide, Flu, Cold, COVID or RSV? How to Tell Them Apart, puts the four illnesses side by side.
Symptoms in adults and older children
In adults and older children, RSV usually causes a mild, cold-like illness. Symptoms typically appear four to six days after exposure: runny nose, nasal congestion, cough, sneezing, sore throat, headache, fatigue and a low-grade fever, sometimes with wheezing. Most healthy adults recover in a week or two, although a cough may linger. Because these symptoms are so ordinary, most adults with RSV never know they had it — and people can pass it on while feeling only mildly unwell, or even before they feel ill at all.
Symptoms in infants and young children
In infants and young children, RSV can look different — and more serious. Early symptoms can include a runny nose, nasal congestion, cough and decreased appetite, with fever early in the illness. The CDC lists RSV symptoms as runny nose, decreased appetite, coughing, sneezing, fever or wheezing; in very young infants, symptoms may also include irritability, decreased activity, or apnea — pauses in breathing lasting more than 10 seconds.
Watch for signs that the illness is moving into the lower airways: wheezing, rapid or laboured breathing, ribs pulling in with each breath, or a baby feeding poorly or taking in much less fluid than usual. A baby who is not drinking enough fluids, is unusually sleepy or hard to wake, or has bluish lips or skin needs emergency care. Most infants with RSV have a mild illness and recover at home — but RSV is the most common cause of hospitalisation in U.S. infants, according to the CDC.
How RSV spreads
RSV spreads through direct contact with the virus, such as when droplets from an infected person’s cough or sneeze reach your eyes, nose or mouth, or by touching a contaminated surface — a doorknob or a toy — and then touching your face. Children often pass RSV to each other at school or daycare and then bring it home, and older children are a common route by which the virus enters a household.
People with RSV are usually contagious for three to eight days, starting one to two days before symptoms appear, though some infants and people with weakened immune systems can remain contagious for up to four weeks. The virus can survive for hours on hard surfaces, which is why hand hygiene and cleaning frequently touched surfaces matter so much during RSV season.
How long does RSV last?
Most people recover within about a week or two, although a cough may last for weeks. There is no specific antiviral treatment for RSV in most cases; care focuses on rest, fluids and relieving symptoms. Antibiotics are not used, because RSV is a viral infection. For how RSV compares with the other winter viruses, see Flu, Cold, COVID or RSV? How to Tell Them Apart; for the flu’s timeline, see How Long Does the Flu Last? A Day-by-Day Timeline. Testing can distinguish RSV from flu and COVID-19, which matters because those two have antiviral treatments that work best when started early; there is no widely used home test for RSV.
Who is most at risk?
RSV can affect anyone, but the CDC identifies these groups as being at highest risk of severe disease:
- Infants, especially those under 12 months old, and premature babies.
- Adults aged 75 and older, and adults aged 50 to 74 with chronic heart or lung disease, a weakened immune system or certain other underlying conditions.
- People living in nursing homes or other long-term care settings.
- Children and adults with weakened immune systems.
- Children with chronic lung disease or significant congenital heart disease.
Age is the strongest risk factor at both ends of life: in babies, airways are so narrow that even mild inflammation can make breathing hard, while in older adults a weaker immune response combines with heart or lung conditions that RSV can worsen.
Caring for someone with RSV at home
For mild RSV, care at home is about comfort and watching for changes: keep fluids going, rest as much as possible, and use fever or pain relief as directed by your clinician. Never give aspirin to children. Keeping the air free of smoke matters, especially around babies.
The CDC’s guidance is to stay home while unwell and return to normal activities only once symptoms have been getting better overall for at least 24 hours and you have been fever-free for at least 24 hours without fever-reducing medicine, followed by five days of added precautions. Seek care promptly if a baby is feeding poorly, taking in much less fluid than usual, breathing rapidly or with effort, wheezing, unusually sleepy, or showing pauses in breathing. For adults, seek care for worsening shortness of breath, chest pain, confusion, persistent vomiting, or symptoms that improve and then return worse.
Prevention: everyday steps
There is no single way to prevent RSV, but everyday habits reduce the risk. Wash hands often with soap and water for at least 20 seconds, and help young children do the same. Cover coughs and sneezes with your arm or elbow, avoid touching your face with unwashed hands, and avoid close contact with people who are sick. Clean frequently touched surfaces such as toys and doorknobs, and keep babies away from crowds and from people with cold-like symptoms during RSV season.
Vaccines and preventive antibodies in 2026
Prevention has changed fast: there are now three licensed RSV vaccines for adults and two preventive antibody products for babies, and the CDC confirms the following as current in 2026.
For older adults. The CDC recommends a single dose of RSV vaccine for all adults aged 75 and older, and for adults aged 50 to 74 at increased risk of severe RSV illness. The three FDA-licensed vaccines are GSK’s Arexvy, Moderna’s mResvia and Pfizer’s Abrysvo, with no CDC preference between them. It is not an annual vaccine: one dose protects for at least two years. The best time to be vaccinated is late summer and early fall.
For pregnant women. The CDC recommends a one-time dose of RSV vaccine for pregnant women from week 32 through week 36 of pregnancy, given from September through January in most of the United States, to protect their infants during the first six months of life; Pfizer’s Abrysvo is the vaccine used.
For babies. Most babies need only one of two options: the mother is vaccinated during pregnancy, or the baby receives a preventive antibody. The antibody products are nirsevimab, sold as Beyfortus, and clesrovimab, sold as Enflonsia. Nirsevimab is a single dose for babies under eight months old born during or entering their first RSV season, protecting for at least five months; clesrovimab was recommended by the CDC’s Advisory Committee on Immunization Practices in June 2025 as a second option. High-risk children aged eight to 19 months are also recommended to receive nirsevimab before their second RSV season.
These are preventive antibodies, not vaccines: they deliver ready-made antibodies directly, and their protection covers a single RSV season. Eligibility and timing vary by country, so parents should confirm the details with their paediatrician; in the UK, RSV vaccination follows NHS eligibility rules, which differ from the U.S. schedule.
When is RSV season?
In the United States, RSV epidemics typically run from fall through spring, with the infant antibody products generally given from October through March. In the UK and Australia, RSV also peaks in the cooler months.
The bottom line
RSV is a common virus most people meet in childhood and again as adults, usually as a mild cold. Its danger is concentrated in babies under one and in older adults, where it can cause bronchiolitis and pneumonia. Symptoms appear four to six days after exposure, people are usually contagious for three to eight days, and most recover within a week or two. Prevention now includes a single-dose vaccine for older adults, vaccination in late pregnancy, and long-acting antibodies for babies. If a baby is struggling to breathe or feed, or an older adult is getting worse rather than better, do not wait: get medical help.
This article is for general information only and is not medical advice. If you are worried about a baby in your care, contact a healthcare professional.
Sources
- Centers for Disease Control and Prevention (CDC), “Vaccines for Adults | RSV” — https://www.cdc.gov/rsv/vaccines/adults.html
- CDC, “RSV Vaccine Guidance for Adults” — https://www.cdc.gov/rsv/hcp/vaccine-clinical-guidance/adults.html
- CDC Vaccine Information Statement, “RSV Vaccine: What You Need to Know” — https://www.cdc.gov/vaccines/hcp/current-vis/rsv.html
- CDC, “About RSV” — https://www.cdc.gov/rsv/about/index.html
- CDC, “Clinical Overview of RSV” — https://www.cdc.gov/rsv/hcp/clinical-overview/
- CDC, “Immunizations to Protect Infants” (RSV) — https://www.cdc.gov/rsv/vaccines/protect-infants.html
- Immunize.org, RSV preventive antibody recommendations for infants (summarising CDC/ACIP) — https://www.immunize.org/ask-experts/topic/rsv/rsv-preventive-antibody-infants/
Facts verified against CDC sources on 12 November 2026.
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