Measles: Symptoms, Rash, IgM Test and Immunity

Measles is a highly contagious viral infection that starts like a bad cold, with high fever, cough, runny nose and red, watery eyes, then causes a red, blotchy rash that spreads from the face down the body about 3 to 5 days later. Most people recover within a few weeks, but measles can cause pneumonia, brain swelling (encephalitis) and death, especially in young children, pregnant people and anyone with a weak immune system. There is no antiviral cure. Two doses of a measles vaccine (MMR, or MMRV in the UK childhood schedule) are 97% effective at preventing it, according to the CDC.

Measles is back in the news, in the UK as in the United States. The CDC counted 5,182 confirmed U.S. cases in 2026 as of November 5, 2026, after 2,289 cases in all of 2025. If you have a fever and rash, were exposed, or need to prove you are immune, the right test depends on timing: a swab for RT-PCR and a blood test for measles IgM confirm a current infection, while an IgG test checks immunity.

Key takeaways

• Measles spreads through the air: up to 9 in 10 close contacts without immunity catch it.
• Typical sequence: high fever, cough, runny nose and red eyes, then a rash starting on the face about 14 days after exposure.
• Diagnosis: a nose or throat swab (RT-PCR), ideally with urine, plus a measles IgM blood test. A positive IgG alone means immunity.
• After an exposure, an MMR dose within 72 hours or immune globulin within 6 days can prevent or soften the illness.
• Call your GP surgery or NHS 111 before going in, so you do not expose other patients.

What is measles?

Measles (also called rubeola) is caused by the measles virus. It infects the airways, then immune cells, and spreads through the blood to the skin, lungs, liver and sometimes the brain. Because it attacks immune cells directly, measles weakens the body's defenses for weeks to months after the rash fades.

Measles was declared eliminated from the United States in 2000, meaning it no longer circulated year-round. It still arrives with travellers, and large outbreaks follow in communities with low vaccination rates, as in Texas, New Mexico and Oklahoma in 2025. The virus can linger in a room for up to 2 hours. Before the vaccine, an estimated 48,000 Americans were hospitalised and 400 to 500 died from measles every year.

Worldwide, a 2026 Global Burden of Disease analysis in Nature Medicine estimated 15.6 million measles cases and 118,000 deaths among children under 5 in 2023. The World Health Organization (WHO) estimates that measles vaccination averted nearly 59 million deaths between 2000 and 2024.

Causes and risk factors

You catch measles by breathing air that contains the virus. An infected person is contagious from 4 days before to 4 days after the rash appears, so people often spread it before they know they are sick.

The main risk factor is having no immunity. The CDC lists these groups as most likely to have severe disease:

• children under 5 and adults over 20;
• pregnant people;
• people with weakened immune systems, such as those with leukaemia or HIV;
• children who are malnourished or low in vitamin A, according to the WHO.

In the 2025 U.S. outbreak, 96% of patients reported by April 17 were unvaccinated or had an unknown vaccination status.

Measles symptoms and warning signs

Measles follows a predictable timeline. The CDC's Pink Book gives these averages:

• Days 11 to 12 after exposure: the first symptoms appear (the prodrome). Fever climbs step by step, often to 39.4°C to 40.6°C (103°F to 105°F), with the "three Cs": cough, coryza (runny nose) and conjunctivitis (red, watery eyes). Many people also feel tired and achy, and a headache is common.
• About 1 to 2 days before the rash: Koplik spots, small white or bluish-white dots on a red background inside the cheeks. They are specific to measles.
• About day 14 (range 7 to 21): the measles rash.

What does the measles rash look like?

The measles rash is made of flat red spots, sometimes slightly raised, that start at the hairline and behind the ears, then spread to the face, neck, trunk, arms and legs. The spots often merge into blotches, are usually not itchy, and can be harder to see on brown and black skin, as the NHS notes; fever usually peaks with the rash. The rash lasts 5 to 6 days, then fades in the order it came. Many illnesses cause rashes; our guide to skin rash causes and warning signs explains how they differ. The red eyes of measles can also be mistaken for ordinary pink eye; the combination with high fever and cough is the clue.

Vaccinated people who catch measles often have milder, atypical illness, which makes lab testing more important.

Complications of measles

About 30% of reported U.S. cases from 1987 to 2000 had at least one complication, according to the CDC. The main ones are:

• Diarrhoea and ear infections, which are common and can lead to dehydration or pain.
• Pneumonia, a leading cause of serious illness. In a CDC review of 54 hospitalised patients in West Texas in 2025, 72% had pneumonia and 70% needed oxygen.
• Encephalitis (brain swelling) in about 1 in 1,000 cases, often with lasting brain damage.
• Death in 1 to 3 of every 1,000 infected children, from lung or brain complications.
• SSPE, a rare, fatal brain disease appearing 7 to 10 years after infection. A California study estimated a risk of 1 in 1,367 for children infected before age 5 and 1 in 609 for those infected before 12 months.
• Immune amnesia: measles erases part of the immune system's memory of other germs, which can leave children more vulnerable to other infections afterward.

How is measles diagnosed?

A doctor suspects measles from the symptoms and possible exposure, then confirms it in the lab. Suspected cases are reported to the health department, which often arranges fast testing. The CDC recommends collecting two kinds of specimens at the first visit.

RT-PCR swab and urine test

RT-PCR (reverse transcription polymerase chain reaction) detects the genetic material of the virus. The preferred sample is a nasopharyngeal (back of the nose) or throat swab, and urine can be added. Detection works best from the first day of rash through 3 days after, but can still succeed 10 to 14 days after rash onset. Urine matters more than many people think: in a 2025 Colorado outbreak, two vaccinated patients had negative nose swabs but positive urine tests, and one patient still had a positive urine result 24 days after the rash began.

Measles IgM blood test

IgM is the first antibody the body makes against a new infection. A positive measles IgM points to a current or recent infection. Timing is the catch: IgM may not be detectable until about 3 days after the rash starts, so an early negative result can be falsely reassuring. The CDC advises a second blood sample a few days later if the first was drawn within 3 days of rash onset and RT-PCR was negative or not done. False positives also happen, for example with rheumatoid factor or with other rash illnesses such as parvovirus B19. For how this antibody behaves in general, see our guide to IgM blood test results.

Measles IgG test (titer)

IgG appears a little later and usually stays for life. A positive IgG on its own means past vaccination or infection, so you are considered immune. During an illness, a rise in IgG between two samples taken a couple of weeks apart supports a recent infection. If your question is only "am I immune?", our article on the measles titer test covers when it is useful and when a vaccine record is enough.

Supporting blood tests

Routine tests help judge severity. A complete blood count often shows a low lymphocyte count: 74% of 124 adults hospitalised with measles in Sarajevo in 2024 had lymphopenia. Platelets are occasionally low. In the Sarajevo study, C-reactive protein was raised in 95% and liver enzymes in 75% of patients. In children with severe measles, doctors may also check a vitamin A (retinol) level, although treatment does not wait for the result.

Measles test results: reference values and thresholds

Each laboratory sets its own cut-offs, so read the range printed on your report. Values below are published examples.

How to read your measles results

Read the results together:

• PCR positive, with fever and rash: measles is confirmed. Follow the health department's isolation advice.
• PCR negative, IgM positive: likely a recent infection if you are unvaccinated and were exposed; a false positive is possible when the story does not fit.
• IgM negative in the first 3 days of rash: not yet reassuring. Ask whether a second blood sample or a urine PCR is planned.
• IgG positive, IgM negative, no symptoms: you are immune, the usual result after vaccination.
• IgG negative or equivocal, no symptoms: you may not be protected; vaccination is usually simpler than retesting.
• Rash 7 to 10 days after an MMR jab: this can be a vaccine reaction. Reference labs, including the CDC, can test for the vaccine virus so it is not counted as a measles case.

If your white cell count or liver enzymes are off, our guide to low lymphocytes and our article on liver function tests explain what those numbers mean.

Measles treatment and follow-up

There is no FDA-approved antiviral for measles. Care is supportive: fluids, fever control with paracetamol or ibuprofen (never aspirin in children under 16), rest, and treatment of complications. Antibiotics are not given routinely but treat bacterial ear infections or pneumonia. Ribavirin, an antiviral that blocks viral RNA synthesis, is sometimes considered for severe cases in specialist settings, but it is not FDA-approved for measles.

Vitamin A for measles

The CDC says vitamin A may be given to children with measles under medical supervision, and should be given in severe measles, including all hospitalised children. Doses are given on the day of diagnosis and repeated the next day: 50,000 IU under 6 months, 100,000 IU from 6 to 11 months, and 200,000 IU from 12 months. The WHO recommends this for all children under 5 with suspected measles, with a third dose 4 to 6 weeks later if there are eye signs of deficiency. A Cochrane review found that two doses lowered the risk of death in children under 2. Vitamin A does not prevent measles and does not replace the vaccine. High doses are never self-prescribed, and pregnant people should avoid them. Our vitamin A blood test guide explains what a retinol result means.

Isolation and recovery

People with measles stay at home, away from nursery, school and work, for at least 4 days from when the rash first appears, as the NHS advises. Because of immune amnesia, keep routine vaccines up to date afterward.

Measles prevention: MMR vaccine and post-exposure steps

MMR and MMRV vaccine schedule (UK and US)

• UK children: the NHS now offers the MMRV vaccine (measles, mumps, rubella and chickenpox), usually at 12 months and 18 months, for children born on or after 1 January 2025; older children follow the earlier MMR timings.
• US children (CDC): first dose at 12 to 15 months, second at 4 to 6 years, or earlier, at least 28 days after the first; infants 6 to 11 months can have one early dose before international travel.
• Adults and older children who were not vaccinated: the NHS recommends the MMR vaccine; the CDC advises two doses, 28 days apart, for university students, healthcare workers and international travellers.
• Evidence of immunity: written vaccine records, a positive IgG, lab-confirmed past measles, or birth before 1957.

About 95% of children vaccinated at 12 months or older respond to one dose, and more than 99% after two. Common side effects are mild: fever in 5% to 15% and a rash in about 5%, usually 7 to 12 days after the jab. Febrile seizures occur in about 1 in 3,000 to 4,000 doses. MMR is a live vaccine and is not given during pregnancy; pregnancy should be avoided for 4 weeks after a dose.

After an exposure: act within 72 hours

• MMR vaccine within 72 hours of exposure can prevent measles or make it milder in people without immunity.
• Immune globulin (IG) within 6 days is used when the vaccine is not possible: infants under 12 months, pregnant people without immunity and people with severely weakened immunity. The intramuscular dose is 0.5 mL/kg (maximum 15 mL); severely immunocompromised and pregnant people receive the intravenous form (400 mg/kg).
• MMR and IG are not given at the same time.

A 2025 systematic review estimated the effectiveness of vaccine given after exposure at 83% to 100%, and immune globulin at 76% to 100%, while noting that the studies are small.

Measles in pregnancy, children and older adults

Pregnancy: measles raises the risk of severe illness, miscarriage, premature birth and low birth weight, according to the WHO. MMR cannot be given during pregnancy, which is why immunity is checked before or early in pregnancy, as described in our guide to blood tests during pregnancy. A non-immune pregnant person who is exposed should call a doctor the same day about intravenous immune globulin.

Babies: infants are too young for routine MMR and carry the highest SSPE risk. In the West Texas hospital review, 91% of hospitalised patients were under 18. Children with measles should get vitamin A as described above.

Older adults: people born before 1957 are presumed immune. Adults over 20 who catch measles are at higher risk of severe disease.

When to see a doctor

Ask for an urgent GP appointment or call NHS 111 before going in if you or your child has fever with a rash, or symptoms after a possible exposure, and say measles is possible. Call promptly too if you were exposed and are pregnant, have a weak immune system or have a baby under 1, because the treatment windows are short (72 hours for MMR, 6 days for immune globulin).

Call 999 for emergency signs: trouble breathing, bluish lips, a seizure, being unable to stay awake or confused, a child who is limp or floppy, a rash that does not fade when you press a glass against it, a stiff neck, signs of dehydration (no urine for 8 hours or more, no tears), or a baby who will not feed.

Latest scientific advances in measles

Recent U.S. outbreaks show who ends up in the hospital

CDC investigators reviewed 54 patients hospitalised in West Texas in early 2025. All were unvaccinated or had an unknown status, 89% had no underlying condition, and 72% had pneumonia. About 1 in 5 people with measles in that outbreak needed hospital care. What it means for you: measles is not "just a rash" for healthy children.

Urine samples and wastewater catch cases that swabs miss

A 2026 CDC report on a Colorado outbreak found measles RNA in urine when nose swabs were negative in vaccinated patients, and the authors recommend routine urine collection. In Wisconsin, wastewater testing detected one imported case before it was identified clinically, and also revealed that a widely used assay missed a circulating B3 variant, which was then fixed. What it means for you: a urine sample raises the chance of a correct answer.

Measles erases immune memory

A landmark 2019 study in Science found that measles wiped out 11% to 73% of children's existing antibody repertoire, an effect not seen after MMR vaccination. NIAID is now studying immune amnesia after measles in Africa (NCT06153979). What it means for you: the vaccine protects against more than measles itself.

Vaccine patches and third doses

In a 2024 Lancet trial in The Gambia, a measles and rubella microneedle patch made 93% of infants seroconvert to measles, compared with 90% after a standard injection, with only mild skin reactions. In Canada, an ongoing study is testing whether a third MMR dose benefits adults (NCT05923970). What it means for you: easier vaccines may help close coverage gaps, but a third dose is not routinely recommended in the UK or the U.S. today.

Which tests can help?

If measles is suspected, the decisive tests are an RT-PCR swab with urine and a measles IgM blood test. To check immunity, an IgG test is enough. Alongside them, a complete blood count, CRP, liver enzymes and electrolytes show how hard the infection hits. Tests that separate viral from bacterial infections can guide antibiotic decisions, as our article on a blood test for bacterial or viral infection explains. A rash that started after antibiotics may be a drug reaction, as in our guide to amoxicillin rash. Our page on platelet levels gives the normal range.

Glossary

• Coryza: runny, stuffy nose.
• Koplik spots: small white spots inside the cheeks that appear shortly before the measles rash.
• RT-PCR: a lab method that detects the virus's genetic material in a swab, urine or blood.
• IgM: the first antibody made against a new infection; it fades within weeks.
• IgG: the long-lasting antibody that shows immunity from vaccination or past infection.
• Titer: a measure of how much antibody is in the blood. See also our IgG blood test guide.
• Lymphopenia: a low number of lymphocytes, a type of white blood cell.
• SSPE: subacute sclerosing panencephalitis, a late brain complication of measles.
• Immune amnesia: loss of immune memory against other germs caused by measles.

Frequently asked questions

How is measles diagnosed?

By symptoms and exposure history, confirmed with an RT-PCR test on a nose or throat swab (and urine) and a measles IgM blood test.

What are the early symptoms of measles?

High fever, cough, runny nose, red watery eyes and fatigue, starting about 11 to 12 days after exposure. Koplik spots inside the cheeks can appear 1 to 2 days before the rash.

Do you get headaches with measles?

Yes. Headache is common with the high fever of the early phase. A severe headache with a stiff neck, confusion, drowsiness or seizures can signal encephalitis and needs emergency care.

How many died from measles last year?

In 2025, the CDC reported three U.S. measles deaths by April 17, among 2,289 confirmed cases for the full year. Its national page, updated November 6, 2026, lists 4 deaths and notes that this number is subject to change. Worldwide, the WHO estimates about 95,000 measles deaths in 2024.

Should I go to hospital if I have measles?

Usually not straight away: call your GP or NHS 111 first so staff can protect other patients, and most people recover at home. Call 999 for trouble breathing, a seizure, a floppy child or drowsiness. In the United States, 1 to 3 of every 1,000 children with measles die, according to the CDC.

Can you get measles if you are vaccinated?

Rarely. Two doses are 97% effective and one dose 93%. Vaccinated people who do get measles usually have fewer and milder symptoms.

Does a measles rash blanch?

Early measles spots often fade briefly when pressed, but as they merge they may not. The NHS advises calling 999 if a rash does not fade when you press a glass against it, because that can also be a sign of sepsis or meningitis. A mild rash 7 to 10 days after MMR is usually a vaccine reaction, not measles.

Sources

• CDC — Measles Cases and Outbreaks (updated November 6, 2026) — CDC, 2026 — cdc.gov
• CDC — Clinical Overview of Measles — CDC, 2026 — cdc.gov
• CDC — Laboratory Testing for Measles — CDC, 2024 — cdc.gov
• CDC — Measles Serology Testing — CDC, 2024 — cdc.gov
• CDC — Measles Vaccine Recommendations — CDC, 2026 — cdc.gov
• CDC — Pink Book, Chapter 13: Measles — CDC, 2024 — cdc.gov
• MedlinePlus — Measles and Mumps Tests — National Library of Medicine, 2025 — medlineplus.gov
• WHO — Measles fact sheet — World Health Organization, 2026 — who.int
• WHO — Serum retinol concentrations for determining the prevalence of vitamin A deficiency in populations — World Health Organization, 2011 — who.int
• ARUP Laboratories — Measles (Rubeola) Antibodies, IgG and IgM, test 0050375 — ARUP, 2026 — aruplab.com
• Mathis AD et al. — Measles Update, United States, January 1–April 17, 2025 — MMWR, 2025 — doi.org
• Wang D et al. — Characteristics of Patients Hospitalized with Measles During an Outbreak, West Texas, January–March 2025 — MMWR, 2026 — doi.org
• Metz AR et al. — Measles Outbreak Associated with an Infectious Traveler, Colorado, May–June 2025 — MMWR, 2026 — doi.org
• Pray I et al. — Genotype-Specific Detection of Measles Virus Using Wastewater Surveillance, Wisconsin, February 2026 — MMWR, 2026 — doi.org
• McLean HQ et al. — Prevention of measles, rubella, congenital rubella syndrome, and mumps, 2013: ACIP summary recommendations — MMWR Recommendations and Reports, 2013 — pubmed.ncbi.nlm.nih.gov
• Mina MJ et al. — Measles virus infection diminishes preexisting antibodies that offer protection from other pathogens — Science, 2019 — doi.org
• Wendorf KA et al. — Subacute Sclerosing Panencephalitis: The Devastating Measles Complication That Might Be More Common Than Previously Estimated — Clinical Infectious Diseases, 2017 — doi.org
• Huiming Y et al. — Vitamin A for treating measles in children — Cochrane Database of Systematic Reviews, 2005 — doi.org
• Montroy J et al. — Post-exposure prophylaxis for the prevention of measles: a systematic review — Vaccine, 2025 — doi.org
• Adigweme I et al. — A measles and rubella vaccine microneedle patch in The Gambia: a phase 1/2 randomised trial — The Lancet, 2024 — doi.org
• GBD 2023 collaborators — Global and regional burden of measles and vaccine coverage among children under 5 years, 1990–2023 — Nature Medicine, 2026 — doi.org
• Hasanefendić B et al. — Laboratory parameters, clinical characteristics and hemogram-derived indices in adult patients with measles — Medicinski Glasnik, 2026 — doi.org
• Chen RT et al. — Measles antibody: reevaluation of protective titers — Journal of Infectious Diseases, 1990 — doi.org
• NIAID — Investigation of Immune Amnesia Following Measles Infection in Select African Regions (NCT06153979) — ClinicalTrials.gov, 2024 — clinicaltrials.gov
• University of Alberta — Is a Third Dose of MMR(V) Vaccine Beneficial for the Adult Population in Alberta? (NCT05923970) — ClinicalTrials.gov, 2024 — clinicaltrials.gov
• NHS — Measles — NHS, 2025 — nhs.uk
• NHS — MMRV vaccine — NHS, 2026 — nhs.uk

Further reading

• Measles titer test: are you immune?
• White blood cell count: results explained
• Abnormal blood test results: what they mean
• Influenza: symptoms, causes and treatment
• Flu jab 2026: who should get it and when
• Shingles symptoms, spread and testing
• CMV blood test: reading IgG and IgM results

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