In short
One infected person can generate up to 18 further infections, and the virus lingers in the air for two hours. Two vaccine doses prevent it, and vitamin A reduces complications in young children who catch it.
Emergency if: Difficulty breathing, drowsiness or confusion, a fit, a stiff neck, or signs of dehydration in a child with measles — go to an emergency department now.
On your report
WBC / Total Leukocyte Count, Absolute Lymphocyte Count, CRP, Vitamin D (25-OH) +1 more
On this page
01
Extraordinarily contagious
Measles spreads more efficiently than almost any other infection. One person infected by measles can generate up to 18 secondary infections among people who are not immune, and the virus remains active and contagious in the air or on infected surfaces for up to two hours. That means transmission can occur in a waiting room after the infected person has left.
This is why measles returns quickly wherever vaccination rates dip, and why it needs a much higher level of community immunity than most infections to stop circulating. It also explains the standard advice to phone ahead rather than walk into a clinic if measles is suspected, so you can be seen without sitting in a shared waiting area.
02
How the illness unfolds
Symptoms usually begin 7 to 14 days after exposure. The first phase lasts about 4 to 7 days and consists of fever, a runny nose, cough, red and watery eyes, and small white spots inside the cheeks. At this stage it resembles an ordinary heavy cold, and the person is already contagious.
The rash appears 3 to 5 days after the first symptoms, typically starting on the face and behind the ears and spreading downwards over the body. Fever is often high when the rash arrives. On darker skin the rash can be harder to see and may be easier to feel than to spot, so the pattern of spread and the preceding symptoms carry more weight than colour.
03
Complications
Complications are common enough that measles should never be regarded as a harmless childhood rash. They include ear infections, severe diarrhoea, severe breathing problems including pneumonia, blindness, and encephalitis — inflammation of the brain. Measles in pregnancy also carries risks.
Young children, adults, people who are undernourished, and those whose immune systems are weakened fare worst. Measles also suppresses the immune system for months afterwards, leaving people more vulnerable to other infections during that period — one of the less known reasons prevention matters so much.
04
Vaccination
Children should receive two doses of the vaccine to ensure they are immune. Coverage remains short of what is needed: in 2025, about 84% of the world's children received one dose and 77% received both. The gap between those figures is where outbreaks begin, because a single dose leaves a meaningful minority unprotected.
Adults who are unsure whether they had two doses can be vaccinated; there is no harm in an extra dose, and catching up is worthwhile at any age. The vaccine is not given during pregnancy or to people with certain forms of immune suppression, which is exactly why those around them being vaccinated matters. If someone unvaccinated is exposed, prompt vaccination within roughly three days can sometimes prevent or moderate the illness.
05
Treatment and vitamin A
There is no specific antiviral treatment for measles, so care is supportive: fluids, fever control, rest, and treating complications such as bacterial pneumonia or ear infection when they arise. Antibiotics do nothing against the virus itself.
For suspected measles in children under 5, two doses of vitamin A are recommended, given immediately upon diagnosis and repeated the next day. Vitamin A can help prevent other complications including eye damage and blindness. This is a treatment given under medical supervision at specific doses, not a reason to take supplements at home.
06
If you suspect measles
Phone a health service for advice rather than attending in person unannounced, so arrangements can be made to avoid exposing others. Stay at home and away from others, including school and work, for the period advised — generally about four days after the rash appears — and avoid contact with pregnant people, infants and anyone immunosuppressed.
Measles is a notifiable infection in most places, so a suspected case is reported and confirmed by a test, usually of saliva or blood. That reporting is not bureaucracy: it triggers contact tracing and protection of vulnerable people who were exposed, which is how outbreaks are contained.
When to act
Routine — see a doctor
Checking your vaccination history and catching up on missed doses: arrange this at any age, well before any outbreak reaches you.
Same-day — call promptly
Fever, cough, red eyes and a spreading rash — phone ahead for advice rather than attending in person, and stay away from others meanwhile.
Emergency — act now
Difficulty breathing, drowsiness or confusion, a fit, a stiff neck, or signs of dehydration in a child with measles — go to an emergency department now.
Values mentioned in this story
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Sources
- Measles — World Health Organizationwho.int
- Measles — NHSnhs.uk
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