What Is RSV and How Do You Protect Your Little One?

A Little Rei newborn set for 0 to 6 months

Respiratory syncytial virus is so common that essentially every child has had it by the age of two. In an adult it is an ordinary cold. In a baby under one — and particularly under six months — it can move into the smallest airways and cause bronchiolitis, which is the most frequent reason infants are admitted to hospital.

Most babies who get it are fine at home in a week or two. The reason it is worth understanding is that the small proportion who are not tend to deteriorate on day three to five, and the signs that matter are specific enough to watch for.

This post is not medical advice

It is written to help you recognise what you are looking at and ask better questions. If your baby is unwell, contact a doctor. If any of the urgent signs below are present, seek emergency care immediately rather than reading further.

What it looks like

It starts as an unremarkable cold and changes character after a couple of days.

Days 1–2: runny nose, mild cough, sometimes a temperature. Indistinguishable from any other cold.
Days 3–5: the cough worsens, breathing becomes faster, feeding slows, and there may be wheezing or a crackling sound. This is the window where infants get worse.
Days 5–7: usually the turning point, with breathing settling first.
Weeks 2–4: the cough often lingers well after everything else has resolved. That alone is not a cause for concern.

A useful non-obvious signal in small babies is feeding. A baby taking well under half their normal intake is telling you their breathing is taking too much effort to feed properly — infants cannot easily breathe hard and feed at the same time.

The signs that mean get help now

Call emergency services or go to an emergency department if you see any of these.

Pauses in breathing, or breathing that stops briefly. In very young babies this can be the first serious sign.
Working hard to breathe: the skin sucking in under the ribs or at the base of the throat, nostrils flaring, or the abdomen pulling in with each breath.
A grunting noise at the end of each breath.
Blue or grey lips, tongue or face; pale, mottled or unusually cold skin.
Very difficult to wake, floppy, or not responding as they normally would.
Under half of normal feeds over 24 hours, or no wet nappy for 12 hours.
A baby under three months with a temperature of 38°C or above.

Contact a doctor the same day, without waiting, for breathing that is faster than usual, a worsening cough with reduced feeding, a temperature over 38°C in a young infant, or any sense that your baby is deteriorating rather than holding steady. Parental concern that a child is not themselves is treated as a warning sign in clinical guidance for good reason.

What helps at home

There is no treatment that shortens RSV. Antibiotics do not work on it — it is a virus. Care is supportive, and the aim is comfortable breathing and adequate fluid.

Feed little and often. Smaller, more frequent feeds are far easier for a blocked, breathless baby than full ones.
Clear the nose before feeds. Saline drops and a gentle aspirator make a real difference, because babies breathe through the nose.
Keep them upright when awake, and hold them for feeds rather than lying flat. For sleep, still on the back on a flat surface — do not prop the cot or use a wedge.
Watch nappies. Output is the simplest hydration check you have.
Paracetamol or ibuprofen for discomfort or fever, at the correct dose for age and weight, if advised.
Skip cough medicines. They are not recommended for young children and do not help bronchiolitis.

Reducing the risk

Immunisation. There are now two routes — a vaccine given in pregnancy, which passes protection to the baby, and a long-acting antibody injection given to infants. Availability and eligibility vary by country; ask your doctor which applies where you are.
Hand washing, relentlessly, especially before holding a newborn. RSV spreads by droplets and by surfaces, and it survives on hard surfaces for hours.
Keep unwell visitors away from a young baby, and be willing to say so. A cold in an adult is bronchiolitis in a newborn.
No smoking anywhere near the baby, including on clothes. Tobacco smoke exposure meaningfully increases the risk of severe disease.
Breastfeed if you can — it is associated with a lower risk of severe infection.
Be cautious with crowds and shared indoor spaces in the first months, particularly during local RSV season.

Who is at higher risk

Babies under six months, and especially under three.
Babies born prematurely.
Babies with congenital heart disease or chronic lung disease.
Babies with a weakened immune system or significant neuromuscular conditions.

If your baby is in one of these groups, ask your doctor in advance what their threshold for review should be, rather than working it out during a bad night. Having a plan agreed beforehand is worth a great deal at 2am.

Questions parents ask

What is RSV in babies?

Respiratory syncytial virus, an extremely common seasonal virus. In adults it is a cold. In infants it can affect the smallest airways and cause bronchiolitis, which is the most common reason babies are admitted to hospital. Nearly all children have had it by age two.

When is RSV most dangerous?

Days three to five of the illness are when infants typically deteriorate, and the risk is highest in babies under six months, those born prematurely, and those with heart, lung or immune conditions.

What are the emergency signs of RSV in a baby?

Pauses in breathing, skin sucking in under the ribs or at the throat, grunting with each breath, blue or grey lips or face, being very difficult to wake, taking under half of normal feeds, or no wet nappy for 12 hours. Any of these means emergency care now.

Is there a vaccine for RSV?

There are two approaches: a vaccine given during pregnancy that passes protection to the baby, and a long-acting antibody injection given directly to infants. Eligibility and availability differ between countries, so ask your doctor what applies where you live.

How long does the cough last after RSV?

Often two to four weeks, well after breathing and feeding have returned to normal. A lingering cough on its own, in a baby who is otherwise well and feeding normally, is usually not a concern.

Sources

This guide is general information, written to help you understand a topic and ask better questions — it is not medical advice and does not replace your own doctor, midwife or paediatrician. Anything that worries you about your baby belongs with them.

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