Every winter, “RSV” comes up at nurseries and children’s clinics. RSV (respiratory syncytial virus) is described by the US Centers for Disease Control and Prevention (CDC) as a common respiratory virus that infects the nose, throat, respiratory tract and lungs. It usually causes mild, cold-like symptoms, but the symptoms aren’t specific, so it can be hard to tell apart from a cold, flu or COVID-19. It spreads in autumn and winter and usually peaks in December and January. Symptoms appear 4 to 6 days after infection, and most infections go away on their own in a week or two. But infants under 6 months and older adults are more likely to become seriously ill, and RSV is the most common cause of bronchiolitis and pneumonia in children under 1. This sets out three CDC RSV pages.
1. Symptoms 4 to 6 days after infection; most recover in 1 to 2 weeks. Peaks in December and January.
2. Usually contagious for 3 to 8 days — some infants and people with weak immune systems for 4 weeks or longer, even after symptoms stop.
3. Difficulty breathing, not drinking enough, or worsening symptoms: seek care. Very young infants may only be irritable, less active or breathing with difficulty.
RSV in numbers — CDC
| What | What the CDC says | Worth noting (our gloss) |
|---|---|---|
| Symptoms appear | 4 to 6 days after infection | — |
| Recovery | Most on their own in a week or two | — |
| Contagious | Usually 3 to 8 days; may start a day or two before symptoms | — |
| Contagious (exception) | Some infants and people with weakened immune systems 4 weeks or longer, even after symptoms stop | No symptoms doesn’t mean not contagious |
| Season | Autumn and winter; usually peaks in December and January | US data |
| Higher risk | Infants under 6 months, older adults, adults with certain risk factors | — |
The December–January peak is US data; we haven’t checked Korea’s season.
Symptoms — CDC
- Runny nose, congestion, decreased appetite
- Coughing, sneezing, fever
- Wheezing
The CDC says these usually appear in stages, not all at once. In very young infants, the only symptoms may be irritability, decreased activity and breathing difficulties — so no fever or cough isn’t reassurance on its own (our reading). RSV can also worsen COPD or asthma.
Fever in babies is in baby fever, and baby coughs and colds in baby cough and cold.
When to seek care — CDC
Contact a healthcare professional if you or your child:
- Have difficulty breathing
- Are not drinking enough fluids
- Have worsening symptoms
Severe cases in hospital may need extra oxygen, IV fluids or, rarely, a ventilator; such stays are usually only a few days.
How it spreads and how to prevent it — CDC
| Type | What the CDC says | Worth noting (our gloss) |
|---|---|---|
| Spread | Coughs and sneezes, direct contact, touching a contaminated surface then your face | — |
| Surfaces | Survives many hours on hard surfaces such as tables and crib rails; shorter on tissues and hands | Clean often-touched surfaces |
| Prevention | Cover coughs and sneezes, wash or sanitise hands often, clean frequently touched surfaces | See handwashing |
| Prevention | Cleaner air (fresh outside air, purifying indoor air); stay home when sick | — |
| Immunisation | Recommended for infants, some young children, and older adults or adults with risk factors | Ages and weeks not on this page |
Handwashing steps are in handwashing for 20 seconds. US immunisation criteria may differ from Korea’s, so ask a paediatrician or public health centre (our view).
Checklist
- ☐ Wheezing after a runny nose and cough
- ☐ For babies, irritability, low activity or laboured breathing alone is reason for care
- ☐ Difficulty breathing, not drinking, or getting worse: seek care
- ☐ Contagious 3 to 8 days; babies can be 4 weeks or more
- ☐ Wash hands, wipe toys and crib rails, ventilate
Questions that remain
How do I tell it from a cold?
The CDC says RSV symptoms aren’t specific, so it can be hard to tell from a cold, flu or COVID-19. General cold advice is in common cold, and flu in cold or flu.
How do I care for it at home?
The three pages we read don’t cover home care for fever and pain.
Bronchiolitis in babies, most often caused by RSV, has its own NHS page — worst on days 3 to 5, cough usually better in 3 weeks (bronchiolitis).
Sources
- CDC — Symptoms of RSV — source (page shows: 20 February 2026; checked 14 October 2026). Symptoms, 4 to 6 days, very young infants, when to seek care, a week or two.
- CDC — About RSV — source (page shows: 30 December 2025; checked 14 October 2026). Definition, December–January peak, under 6 months, bronchiolitis and pneumonia under 1, immunisation groups, hospital care.
- CDC — How RSV Spreads — source (page shows: 20 February 2026; checked 14 October 2026). 3 to 8 days, 4 weeks or longer, surfaces, prevention.
- Not read. Korean agency guidance and Korea’s RSV season; the CDC vaccine detail pages.
- What we added. The “worth noting” column.
Where else to check
- A paediatrician — if a baby struggles to breathe or feed, and about immunisation.
Written on 14 October 2026. The content is from the CDC; the glosses are ours. It does not replace diagnosis or treatment.
