Quick answer: RSV (Respiratory Syncytial Virus) is a leading cause of hospitalisation in babies under 12 months — but it’s also an infection that most older children and adults experience as a mild cold.
RSV (Respiratory Syncytial Virus) is a leading cause of hospitalisation in babies under 12 months — but it’s also an infection that most older children and adults experience as a mild cold. The severity depends heavily on age, with the youngest babies most at risk. Here’s what every parent needs to know before winter.
What RSV Is
RSV is an extremely common respiratory virus — virtually all children are infected at least once by age 2, and most adults are reinfected repeatedly throughout life (immunity is partial and short-lived). In older children and adults, RSV causes a cold. In babies, particularly those under 6 months, RSV can cause bronchiolitis — inflammation of the small airways (bronchioles) in the lungs — which can significantly impair breathing. RSV season typically runs October through March in the Northern Hemisphere. It spreads through droplets and contaminated surfaces; it can survive on hard surfaces for several hours.
RSV Symptoms in Babies
RSV typically begins with upper respiratory symptoms (runny nose, mild fever, mild cough) that progress over 2–5 days. In babies who develop bronchiolitis: increasingly fast breathing (tachypnoea), laboured breathing with visible effort (nasal flaring, ribs showing, skin pulling in at the throat), persistent wet or wheezy cough, poor feeding (breathing difficulty makes coordinating sucking, swallowing, and breathing hard), and irritability. Symptoms typically peak at 3–5 days and gradually improve over 1–2 weeks.
When to Go to Hospital
Seek emergency care for: breathing rate above 60 breaths per minute in a baby, nostrils flaring with each breath, skin pulling in between the ribs or at the base of the throat (intercostal and subcostal recession), grunting with each breath, blue or grey colour around the lips (cyanosis), persistently not feeding (less than half normal intake for 2+ feeds), extreme lethargy or difficulty rousing, or apnoea (breathing pauses — any apnoea in a baby under 6 months requires emergency evaluation). Call your doctor or go to A&E / ER immediately for any of these.
Treatment: What Works (and What Doesn’t)
There is no antiviral treatment for RSV. Treatment is supportive: Nasal saline and suction: The most effective home intervention — saline drops followed by nasal bulb suctioning can significantly improve feeding and breathing by clearing mucus from the narrow nasal passages. Do this before feeds. Upright positioning: Semi-upright positioning (using a wedge or holding upright after feeds) reduces respiratory effort. Never prop in a car seat for unsupervised sleep. Small frequent feeds: Smaller volumes more often reduce the breathing work per feed. Hydration: Maintain feeding as best possible. Hospital: Oxygen supplementation, IV fluids, and monitoring are the mainstays of hospital treatment for severe cases. Most hospitalised babies can be discharged within a few days.
Protecting your baby from RSV: two pathways
Current NHS and CDC guidance (from 2024–2025) offers two routes to protect babies from severe RSV — and which applies depends on timing.
- Maternal RSV vaccine (Abrysvo): Offered to pregnant women at 28–36 weeks of pregnancy. The vaccine stimulates the mother’s immune system to produce antibodies that cross the placenta and protect the baby from birth. NHS England introduced Abrysvo on the national programme from September 2024, offered to all pregnant women in the eligible window. If you are pregnant, ask your midwife about the RSV vaccine at your antenatal appointments from 28 weeks.
- Infant nirsevimab (Beyfortus): A monoclonal antibody injection given to babies directly — it provides passive immunity rather than activating the immune system. Recommended for babies born during or shortly before RSV season (October–March) and for babies under 8 months entering their first RSV season. NHS England introduced nirsevimab in the 2023–2024 season. If the mother was not vaccinated during pregnancy, nirsevimab is offered to the baby.
- Which pathway applies: If the maternal vaccine was given in pregnancy at 28+ weeks, the baby receives passive protection from birth — nirsevimab may not be needed. If the mother was not vaccinated (vaccine given before the NHS programme, declined, or delivered preterm before adequate transfer), nirsevimab is offered to the baby. Discuss with your midwife or health visitor.
Both nirsevimab and the maternal vaccine significantly reduce RSV-related hospitalisation — trials showed approximately 80% reduction in severe RSV bronchiolitis. Neither prevents RSV infection entirely but substantially reduces severity.
Frequently Asked Questions
My baby has RSV — when will they get better?
Bronchiolitis from RSV typically peaks at 3–5 days and then gradually improves over 7–14 days. The cough can persist for 3–4 weeks as the airways heal. Most babies are significantly better within 2 weeks. If your baby is not improving after 5 days, contact your GP.
Can RSV cause long-term breathing problems?
Children who have severe RSV bronchiolitis in infancy have slightly increased rates of recurrent wheezing and asthma diagnosis in early childhood. Whether RSV causes asthma or whether susceptible children are more likely to both have severe RSV and develop asthma is still debated. The nirsevimab antibody may reduce this risk.
My 2-year-old has RSV but seems fine — why is my newborn worse?
RSV severity decreases markedly with age. By 2 years, most children have larger, more developed airways that tolerate inflammation much better, and partial immune memory from previous RSV exposures. Newborns have narrow airways (a small amount of inflammation causes significant obstruction), immature immune responses, and no prior RSV exposure. This is why the same virus can cause a mild cold in a toddler and severe bronchiolitis in their newborn sibling.
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