Respiratory syncytial virus (RSV) is an infection that nearly all infants will contract by the age of two. Most suffer only mild, common cold-like symptoms which soon go away with no need for diagnosis or treatment. But in a small number of cases, infant RSV can quickly develop into a medical emergency.1
What is RSV?
Not a rare disease at all, RSV is a common virus that will affect most of us many times in our lives. It is highly contagious and occurs mainly in the cold and flu season. In a healthy individual, the symptoms of RSV are like those of the common cold. Many of us will have had it without knowing it. For most babies, like adults, RSV causes only mild respiratory symptoms. However, for some – especially babies at high risk – RSV can develop into a potentially fatal illness necessitating treatment in hospital.2
Risk factors for RSV
Infants at a heightened risk of developing severe RSV infection include those born prematurely or with underlying lung or heart issues, as well as the following groups:3
- Premature babies
Infants who are born prematurely (born at 35 weeks or less), and who are six months of age or younger at the beginning of RSV season. A premature baby’s lungs and airways are much smaller than those of a baby born at full term. The smaller the airways, the greater the risk of blockage and even lung damage. In addition, premature babies will be short of antibodies – proteins that fight off harmful germs and viruses.
- Babies with lung conditions
Infants who have a chronic lung condition known as BPD/CLDP (bronchopulmonary dysplasia/chronic lung disease of prematurity) that required medical treatment within the previous 6 months, and who are 24 months of age or younger at the beginning of RSV season.
- Babies with heart conditions
Infants who have a heart condition known as HS-CHD (haemodynamically significant congenital heart disease), and who are 24 months of age or younger at the beginning of RSV season. - Children with neuromuscular Issues
Those with neuromuscular issues that hinder a child from adequately clearing their airway face an increased risk of severe RSV infection. The compromised ability to effectively manage airway secretions can contribute to respiratory complications. - Infants and children with congenital lung abnormalities
Children with congenital lung abnormalities are at an elevated risk for severe RSV infection. Anomalies in lung structure and function can exacerbate respiratory challenges, making them more susceptible to complications. - Immunocompromised infants and children
Infants and children with weakened immune systems face a heightened risk of severe RSV infection. The compromised ability to mount a strong immune response increases susceptibility to respiratory infections.
While any infant can potentially develop a severe RSV infection, recognising these additional vulnerable groups is important for implementing appropriate preventive measures and interventions.
What are the symptoms of RSV?
RSV typically starts with mild cold symptoms:
- Congestion
- Runny nose
- Fever
- Sore throat
- Coughing
- Sneezing
- Wheezing
Signs of RSV in babies may include irritability and fatigue and difficulty in breathing. These may be the only signs in some infant cases. Usually, these symptoms will clear after a few days.4 Adults may have RSV asymptomatically – without realising they have it. This can cause infected people to spread the illness unknowingly.

Why is RSV on the rise?
Since the COVID-19 pandemic, there has been a drastic increase in the frequency of RSV infections in children. The reasons are uncertain but possible explanations include:5
- Reduced immunity to RSV in certain age groups because of the virus circulating less at the start of the pandemic
- Potential changes in the immune system caused by the virus that causes COVID-19
- The ways in which the RSV and COVID viruses might interact
- Changes in how people seek healthcare6
Possible complications of RSV
RSV can lead to more severe infections, including:
- Bronchiolitis – an inflammation that causes swelling and a build-up of mucus in in the small airways of the lungs
- Pneumonia – a lung infection that causes inflammation and difficulty in breathing
RSV is the most common cause of bronchiolitis and pneumonia in children under 1 year of age.7
RSV can also make pre-existing health problems worse. For example, people with asthma may experience asthma attacks as a result of RSV infection, and people with congestive heart failure may experience more severe symptoms triggered by RSV.8
How is RSV diagnosed?9,10
In most cases, healthcare professionals will diagnose RSV on clinical symptoms alone, without specific testing. As it’s a common and generally mild disease in babies, infants and adults, formal tests are rarely needed.
Doctors may order a nose or mouth swab, to check for white blood cell counts and look for viruses. They will do this in more severe cases or in situations where confirmation is needed. They may also order chest X-rays in some cases.
What causes RSV?11
RSV is a respiratory virus that commonly affects the lungs and airways, especially in young children and infants.
RSV is highly contagious. It spreads from person to person through close contact via coughing and sneezing or touching contaminated objects or surfaces.12 The virus can live outside of the human body for many hours. Children can easily pick up the virus when they touch contaminated toys and then put their fingers in their mouths.
The incubation period – the time from infection to symptoms developing – is typically 3 to 5 days.13
How long does RSV last?
In healthy children and adults, RSV symptoms typically last about 1 to 2 weeks. The symptoms can vary in duration and severity depending on factors such as age and overall health.
People infected with RSV usually remain contagious for 3 to 8 days. They may become contagious a day or two before they start showing signs of illness. However, some infants, and people with weakened immune systems, can continue to spread the virus even after they stop showing symptoms, for as long as 4 weeks.14
How to prevent RSV15
Here are some practical measures we can take to avoid catching RSV or to avoid spreading it if we have it:
Keep your hands clean
Wash your hands frequently with soap and water for at least 20 seconds, and help young children to do the same.
Avoid touching your face with unwashed hands
Avoid touching your eyes, nose, and mouth with hands that haven't been washed.
Avoid close contact with people who are ill
Avoid intimate contact, such as kissing, and refrain from sharing cups or utensils with individuals displaying cold-like symptoms.
Follow cough and sneeze etiquette
Cover your mouth and nose with a tissue or the upper sleeve of your shirt when coughing or sneezing. Dispose of used tissues promptly in the wastebin.
Sanitise frequently touched surfaces
Clean surfaces and objects that are frequently touched, including toys, doorknobs, and mobile devices.
Stay at home if you’re unwell
If you can, remain at home and avoid work, school, and public spaces when you're unwell.16
Medication and vaccine for preventing RSV
Medications have been developed for the prevention of RSV. These are not technically vaccines, but monoclonal antibody treatments – although there are two RSV vaccines available for adults over 60 years of age and for pregnant women in some cases. The antibody treatments may be recommended for at-risk infants. Different treatments are approved for differing circumstances in different countries. Public health experts are prioritising babies at highest risk of serious illness for the RSV immunisation.17
Related links
RSV: When It's More Than Just a Cold – healthychildren.org
If you are the parent of a baby or young child, you may have questions about RSV and how to prevent it. Read on to learn more.
RSV Symptoms and Diagnosis – American Lung Association
RSV is the leading cause of hospitalisation in all infants. Find out when to contact your child’s healthcare provider.
Immunology
The role of the immune system
References:
1RSV. American College of Emergency Physicians.
https://www.emergencyphysicians.org/article/know-when-to-go/rsv
2RSV and Infants: a Respiratory Disease That Can Be Deadly. American Lung Association.
https://www.lung.org/blog/about-rsv-and-infants
3RSV in Infants and Young Children. CDC. Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/high-risk/infants-young-children.html
4RSV Symptoms and Diagnosis. American Lung Association.
https://www.lung.org/lung-health-diseases/lung-disease-lookup/rsv/symptoms-diagnosis
5Why has the epidemiology of RSV changed during the COVID-19 pandemic? eClinicalMedicine. The Lancet.
https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00266-3/fulltext
6Why has the epidemiology of RSV changed during the COVID-19 pandemic? eClinicalMedicine. The Lancet.
https://www.thelancet.com/journals/eclinm/article/PIIS2589-5370(23)00266-3/fulltext
7Respiratory Syncytial Virus Infection (RSV). Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/about/symptoms.html
8RSV in Older Adults and Adults with Chronic Medical Conditions. CDC. Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/high-risk/older-adults.html
9RSV Symptoms and Diagnosis. American Lung Association.
https://www.lung.org/lung-health-diseases/lung-disease-lookup/rsv/symptoms-diagnosis
10Low Levels of RSV Testing Among Adults Hospitalized for Lower Respiratory Tract Infection in the United States. Mark H. Rozenbaum et al. National Library of Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9883084/
11,12RSV Transmission. CDC. Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/about/transmission.html
13Respiratory syncytial virus (RSV): symptoms, transmission, prevention, treatment. NHS.
https://www.gov.uk/government/publications/respiratory-syncytial-virus-rsv-symptoms-transmission-prevention-treatment/respiratory-syncytial-virus-rsv-symptoms-transmission-prevention-treatment
14RSV Transmission. CDC. Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/about/transmission.html
15,16RSV in Infants and Young Children. CDC. Centers for Disease Control and Prevention.
https://www.cdc.gov/rsv/high-risk/infants-young-children.html
17RSV: When It's More Than Just a Cold. healthychldren.org.
https://www.healthychildren.org/English/health-issues/conditions/chest-lungs/Pages/RSV-When-Its-More-Than-Just-a-Cold.aspx
Apr, 2024