RSV in Babies: What Every UK Parent Needs to Know

Respiratory syncytial virus — RSV — is one of the most common viruses in the world. Almost every child has been infected by the age of two. In older children and adults, RSV causes nothing more than a cold. In babies, particularly those under six months, it can cause serious illness.

RSV is responsible for around 80 per cent of bronchiolitis cases in the UK, and it is the single biggest cause of infant hospitalisation during winter months. Understanding the virus, knowing what to watch for, and being aware of the new prevention options available in the UK can make a significant difference.

What RSV Is

RSV is an RNA virus that infects the respiratory tract. In babies under one, the virus can travel into the lower respiratory tract — the bronchioles and alveoli — causing them to inflame and fill with mucus. This is bronchiolitis.

The virus spreads through respiratory droplets when an infected person coughs or sneezes, and through contact with contaminated surfaces. It can survive for several hours on hard surfaces, which is why it moves so efficiently through households with older siblings attending nursery or school.

RSV season in the UK typically runs from October through to March, with a peak around December and January.

Why Under-Twos Are High Risk

Babies' airways are very small. Even modest swelling and mucus production — which an older child or adult barely notices — can significantly narrow the airway in a small baby, making breathing laboured and feeding difficult.

Babies also have immature immune systems. They cannot mount a response to RSV as efficiently as older children. Their immune systems have not encountered the virus before and have no pre-formed defences against it.

The highest-risk group is babies under three months. Premature babies and those with chronic lung disease, congenital heart disease, or immune system problems are also at high risk of severe illness.

Symptoms of RSV in Babies

RSV infection begins with cold-like symptoms and may develop into bronchiolitis:

Early symptoms (days 1–3):

• Runny nose, often with clear or slightly yellow mucus
• Sneezing
• Low-grade temperature
• Reduced appetite

Progressive symptoms (days 3–5):

• Worsening cough, often dry and persistent
• Fast breathing — more than 60 breaths per minute in babies under two months is a concern
• Wheeze, particularly on breathing out
• Visible effort when breathing — nostrils flaring, muscles pulling in below the ribs or between the ribs
• Poor feeding — taking less than half the usual amount

Severe symptoms — seek help immediately:

• Blue or grey tinge to lips, tongue, or fingernails
• Grunting with each breath
• Very laboured breathing with significant chest recession
• Prolonged pauses in breathing
• Extreme lethargy or limpness

New RSV Prevention Options in the UK

From the 2024/25 season, the UK introduced a national immunisation programme using nirsevimab, marketed as Beyfortus. This is not a vaccine — it is a long-acting monoclonal antibody that provides immediate, passive protection against RSV.

How nirsevimab works

A monoclonal antibody is a laboratory-made protein that mimics the immune system's ability to neutralise a specific pathogen. Nirsevimab targets the RSV fusion protein, blocking the virus from entering cells. It provides protection for approximately five months — covering the peak RSV season.

Who is eligible

In the UK, nirsevimab is currently offered to:

• All babies born during the RSV season (October to March)
• Babies entering their first RSV season who were born in the preceding spring or summer
• Babies at highest risk of severe RSV disease, including those born prematurely and those with congenital heart disease or chronic lung disease, who may be eligible for additional doses

What to do

Speak to your midwife before discharge from the postnatal ward, or contact your health visitor. The injection is given as a single intramuscular dose. It does not replace the childhood vaccination schedule — it is an additional protection specifically against RSV.

Previously, only the highest-risk babies received palivizumab (Synagis) monthly during RSV season. The introduction of nirsevimab to the wider programme represents a significant step forward in protecting UK infants.

Treatment of RSV / Bronchiolitis

There is no antiviral treatment for RSV in most babies. Management is supportive:

At home:

• Maintain feeds — frequent, smaller feeds if needed
• Saline nasal drops to ease congestion before feeds
• Upright positioning where safe and practical
• Paracetamol for temperature and discomfort (following age-appropriate NHS guidelines)
• Avoid smoke exposure
• No over-the-counter cough or cold medicines

In hospital:

• Supplemental oxygen via nasal cannula or mask
• Nasogastric tube feeding when oral intake is insufficient
• High-flow nasal cannula oxygen in more severe cases
• Monitoring of oxygen saturation, heart rate, and respiratory rate

The vast majority of babies managed in hospital improve within three to five days.

Preventing the Spread of RSV

Beyond immunisation, the most effective steps are:

• Thorough handwashing — the single most effective intervention
• Avoiding contact between very young babies and people with cold symptoms where possible
• Asking visitors to wash hands before handling the baby
• Keeping dummies, feeding equipment, and toys clean
• Avoiding crowded indoor spaces during peak RSV season in the first weeks of life

RSV cannot be eliminated from the environment, but sensible precautions reduce a baby's exposure during the most vulnerable period.

When to Seek Help

If your baby is under three months and develops any respiratory symptoms, monitor closely and have a low threshold for contacting your GP or calling NHS 111. Trust your instincts. If something feels wrong — your baby is breathing differently, feeding much less, or seems very unwell — seek assessment. It is always appropriate to ask.