Measles

Table of Contents

  1. Overview
  2. Epidemiology
  3. Pathophysiology
  4. Etiology and Risk Factors
  5. Clinical Presentation
  6. Diagnosis
  7. Treatment
  8. Complications
  9. Prognosis
  10. Prevention
  11. Recent Research and Advances
  12. Research Papers
  13. Connections
  14. Featured Videos

1. Overview

Measles (also called rubeola) is a highly contagious viral illness that causes high fever, a head-to-toe rash, and a constellation of respiratory and eye symptoms. It is caused by the measles virus, a member of the paramyxovirus family. For most of human history measles was a near-universal childhood infection — almost everyone caught it before adulthood — and it remains one of the leading vaccine-preventable killers of children worldwide.

It is tempting to think of measles as a mild "childhood illness," but that picture is misleading. Measles is one of the most contagious diseases known to science, and in a meaningful fraction of cases it causes serious harm: pneumonia, brain inflammation, deafness, miscarriage and premature birth in pregnancy, a rare but uniformly fatal delayed brain disease, and a striking phenomenon called immune amnesia in which the virus erases years of immune memory to other infections. Before vaccination, measles killed an estimated 2.6 million people every year worldwide.

The single most important fact about measles is also the most hopeful one: it is almost entirely preventable. The measles-mumps-rubella (MMR) vaccine, available since the 1960s, is roughly 97% effective after two doses and has decades of safety data behind it. Measles was declared eliminated from the United States in 2000 — meaning no continuous year-round local spread — but falling vaccination rates in some communities have since allowed imported cases to spark outbreaks again. This page explains why measles matters, what it does to the body, and how it is prevented and treated.

2. Epidemiology

Measles spreads more easily than almost any other infectious disease. Its basic reproduction number (R0) — the average number of people one infected person will go on to infect in a fully susceptible population — is generally estimated in the range of 12 to 18. For comparison, seasonal influenza has an R0 of roughly 1 to 2. A systematic review of the R0 of measles found that the long-cited "12–18" figure varies considerably by setting, but there is no doubt that measles sits at the extreme contagious end of the spectrum.

Practically, this means that if a person with measles enters a room of non-immune people, roughly 90% of those susceptible contacts will become infected. The virus is airborne: it travels in tiny respiratory aerosols that linger suspended in the air and remain infectious for up to about two hours after the infected person has left the room. You do not need direct contact to catch measles — sharing the air is enough.

United States Elimination and Resurgence

Because of a sustained childhood vaccination program, the United States declared measles eliminated in the year 2000. Elimination is a technical term: it means the absence of continuous, year-round transmission within the country for at least 12 months. It does not mean the virus disappeared. Measles still circulates in many parts of the world, and travelers regularly import cases into the US.

What determines whether an imported case fizzles out or ignites an outbreak is the level of community immunity. When vaccination coverage is very high, an imported case finds few susceptible people and the chain of transmission breaks quickly. When coverage falls — particularly in clustered communities where many families decline or delay vaccination — an imported case can spread explosively. This is the simple, non-political public-health reality: measles outbreaks track gaps in vaccination coverage. Restoring and maintaining high coverage is what keeps outbreaks small and brief, and protects infants and immunocompromised people who cannot be vaccinated themselves.

3. Pathophysiology

Measles virus is a single-stranded, negative-sense RNA virus in the genus Morbillivirus, family Paramyxoviridae. Humans are its only natural host. The virus enters the body through the respiratory tract and, importantly, targets immune cells — it uses two receptors to gain entry: SLAM/CD150, found on activated T cells, B cells, and other immune cells, and nectin-4, found on the cells lining the airway.

After infection, the virus first replicates in immune cells in the lymph nodes near the airway, then spreads throughout the body in a viremia (virus in the bloodstream), carried inside infected immune cells. This is why measles is so much more than a "rash illness." The virus's preferential infection of memory immune cells is the basis of the immune-amnesia phenomenon discussed below. The familiar rash itself is a T-cell-mediated immune response to virus-infected cells in the small blood vessels of the skin — which is why the rash appears as the immune system gears up, not at the very start of illness.

The same immune-cell tropism explains why the days surrounding the rash are a period of profound, if temporary, immune suppression — leaving the patient vulnerable to the bacterial pneumonias and other secondary infections that cause most measles deaths.

4. Etiology and Risk Factors

The cause of measles is straightforward: infection with the measles virus. There is only one serotype, which is why a single successful vaccination program — and why natural infection — confers lifelong immunity. Anyone who is not immune (never vaccinated, incompletely vaccinated, or never previously infected) is susceptible.

While anyone non-immune can catch measles, certain groups are at much higher risk of severe disease and death:

The major modifiable risk factor at a population level is simply under-vaccination. Low coverage in a community is what converts a contained imported case into a large outbreak.

5. Clinical Presentation

Measles follows a fairly predictable course over about two weeks. After exposure there is an incubation period of roughly 7 to 14 days with no symptoms.

The Prodrome — The Three C's

The illness then begins with a few days of escalating high fever (often 104°F / 40°C or higher) together with the classic triad known as the three C's:

At this stage measles can look like a bad cold or flu, but the combination of all three C's plus a very high, rising fever is a useful clue.

Koplik Spots

One to two days before the rash appears, tiny bluish-white spots on a red base may appear inside the mouth, classically on the inner cheek opposite the back teeth. These are called Koplik spots, and they are essentially unique to measles — a near-diagnostic sign for clinicians who catch them, though they fade quickly and are easy to miss.

The Rash

Around day 3 to 5 of illness, the characteristic maculopapular rash appears: flat-to-slightly-raised red spots that begin at the hairline and face and then spread downward over the trunk, arms, and legs over a few days. The spots often merge into larger blotches. The fever typically peaks as the rash spreads. As the rash fades it may leave a brownish staining and fine peeling. The downward, head-to-foot ("descending") progression is a hallmark that helps distinguish measles from other rashes.

The Contagious Window

A person with measles is contagious from about four days before the rash appears to about four days after it appears. Because the most contagious period begins before anyone knows it is measles — during the cough-and-cold prodrome — the virus often spreads silently before a diagnosis is even suspected. This is exactly why prompt isolation and rapid public-health reporting matter so much.

6. Diagnosis

Measles is often suspected clinically — the combination of high fever, the three C's, Koplik spots, and a descending maculopapular rash in an unvaccinated person, especially with a relevant travel or exposure history. Because measles has become uncommon in many high-coverage countries, clinicians may not have seen a case, so a high index of suspicion is important.

Laboratory confirmation is recommended for suspected cases and typically uses two approaches together:

Suspected measles is a reportable disease. Because of its extreme contagiousness, a suspected case should be reported to local public-health authorities immediately — without waiting for laboratory confirmation. Rapid reporting lets public health isolate the patient, identify and protect exposed contacts (including offering post-exposure prophylaxis), and stop an outbreak before it grows.

7. Treatment

There is no specific antiviral drug that cures measles. Care is supportive: rest, fluids and rehydration, fever and pain control with acetaminophen or ibuprofen, and careful monitoring for complications. Bacterial complications such as pneumonia or ear infection, when they develop, are treated with antibiotics — but antibiotics do nothing against the measles virus itself and are not used to "prevent" complications routinely.

Vitamin A — An Honest Look

The World Health Organization recommends vitamin A supplementation for children with measles, given as two doses on consecutive days. This recommendation rests on real evidence. A landmark randomized controlled trial in South Africa found that high-dose vitamin A in children hospitalized with severe measles reduced deaths and serious complications, and subsequent reviews support a reduction in measles mortality in young children. The biological rationale is sound: measles depletes the body's vitamin A stores, and vitamin A is essential for the integrity of the epithelial surfaces (eyes, airway, gut) that measles damages. Vitamin A treatment also reduces the risk of measles-related blindness, a major cause of childhood blindness in vitamin-A-deficient populations.

It is important to be precise about what this evidence does and does not mean. Vitamin A is a treatment that reduces the severity and mortality of measles once a child is already infected, with the largest benefit in malnourished, vitamin-A-deficient children. It is not a substitute for vaccination, and it does not prevent measles. Taking vitamin A will not stop you from catching the virus, and high doses of vitamin A are themselves toxic — excessive intake can cause liver damage, and is dangerous in pregnancy because it can cause birth defects. Vitamin A should be given for measles under medical guidance at recommended doses, as an adjunct to good supportive care — never as an alternative to the MMR vaccine.

Post-Exposure Prophylaxis

For non-immune people who have been exposed to measles, two interventions can prevent or lessen disease if given quickly:

Anyone with a known exposure who is unsure of their immune status should contact a clinician or public-health department promptly, because the window for these measures is short.

8. Complications

Complications are common enough — and serious enough — that measles cannot honestly be called a harmless childhood illness. They are most frequent in infants, adults, pregnant people, the malnourished, and the immunocompromised.

Pneumonia

Pneumonia is the most common cause of death from measles, particularly in young children. It can be caused directly by the measles virus or by bacteria that take advantage of the measles-weakened immune system and damaged airway. Difficulty breathing in a child with measles is a medical emergency.

Encephalitis

About 1 in 1,000 people with measles develops acute encephalitis (inflammation of the brain), usually within days of the rash. It can cause seizures, and survivors may be left with permanent deafness, intellectual disability, or other neurological damage. Measles can also cause middle-ear infections that lead to permanent hearing loss.

Subacute Sclerosing Panencephalitis (SSPE)

SSPE is a rare, devastating, and uniformly fatal degenerative brain disease that appears on average 7 to 10 years after the original measles infection, when everyone thought the illness was long over. It causes progressive loss of cognitive and motor function, seizures, and ultimately death, and there is no cure. The risk is highest for children infected with measles before age two, and research suggests SSPE may be more common than previously estimated — on the order of 1 in several thousand cases in young children, far higher than older textbook figures. SSPE is one of the most compelling reasons to prevent measles in the first place: the harm can arrive years later, in a child who appeared to fully recover.

Immune Amnesia

One of the most important and underappreciated discoveries about measles is immune amnesia. Because measles virus preferentially infects and destroys memory immune cells, it does something remarkable and harmful: it erases part of the immune system's existing memory of other pathogens the person had already encountered or been vaccinated against.

In 2019, two landmark studies put this on a firm footing. Mina and colleagues, writing in Science, showed that measles infection destroyed a large portion of children's pre-existing protective antibodies against a wide range of other viruses and bacteria — in effect rolling their immune memory backward and leaving them vulnerable to infections they had previously been protected against. A companion study by Petrova and colleagues in Science Immunology showed that measles depletes and incompletely reconstitutes the body's pool of memory B cells, explaining a prolonged period of immune suppression. Earlier population studies by Mina and colleagues (2015) had already found that measles is associated with increased deaths from other infectious diseases for two to three years afterward.

The practical takeaway is striking: measles does not just make you sick for a couple of weeks — it can leave the immune system weakened against many other diseases for years. Vaccination prevents not only measles itself but this hidden, long-lasting erasure of immune protection.

Pregnancy Complications

Measles during pregnancy is associated with an increased risk of miscarriage, stillbirth, premature delivery, and low birth weight, and the illness itself can be more severe in pregnancy. Because MMR is a live vaccine, it is not given during pregnancy — which is why people planning pregnancy are encouraged to confirm immunity beforehand, and why exposed pregnant people without immunity are offered immune globulin.

9. Prognosis

For a well-nourished child in a high-resource setting with access to good supportive care, most measles infections resolve over one to two weeks, and the great majority recover fully. But "most recover" is not the same as "harmless." Even in high-income countries, measles hospitalizes a meaningful fraction of cases, and complications such as pneumonia, encephalitis, deafness, and the years-later threat of SSPE and immune amnesia mean the stakes are real for every case.

Globally, the prognosis is far more serious. In settings with malnutrition, vitamin A deficiency, and limited access to care, the case-fatality rate can be several percent or higher, and measles remains one of the leading vaccine-preventable causes of death in young children. Survivors of natural infection do gain lifelong immunity to measles itself — but at the price of all the risks above, and with no benefit that vaccination does not provide far more safely.

10. Prevention

Prevention is the heart of the measles story, and it is overwhelmingly a success story. The MMR vaccine (measles, mumps, and rubella) is a live attenuated vaccine that is highly effective and has an exceptionally well-documented safety record built over more than half a century of use in billions of doses.

The MMR Vaccine

Community Immunity (Herd Immunity)

Because measles is so contagious, a very high level of population immunity is needed to stop it from spreading. The herd-immunity threshold for measles is about 95% — among the highest of any disease. When at least roughly 95% of a community is immune, the virus cannot find enough susceptible people to sustain a chain of transmission, and outbreaks die out. This is what protects the people who cannot be vaccinated: newborns, pregnant people, and the immunocompromised. When coverage slips below that threshold in a community, the protective wall develops gaps, and imported cases can take hold.

The Vaccine-Autism Claim — Firmly and Factually Corrected

A persistent fear keeping some families from vaccinating is the claim that MMR causes autism. This claim is false, and it is important to state clearly why. It originated in a 1998 paper by Andrew Wakefield that was later found to be not only methodologically worthless but fraudulent — the data were manipulated and undisclosed conflicts of interest were present. The paper was formally retracted by The Lancet in 2010, and Wakefield lost his medical license.

Crucially, the question has since been studied exhaustively in very large, high-quality studies that show no link whatsoever between MMR and autism. Among the strongest:

Taken together, these studies followed well over a million children and consistently found no link. The scientific question is settled: MMR does not cause autism. The real risk lies in not vaccinating — leaving children exposed to a serious, sometimes deadly, entirely preventable disease.

Travel Considerations

Most US measles cases begin as importations from international travel. People traveling internationally should ensure they are fully immune before departure. For this reason, an accelerated schedule is recommended for travel: infants 6–11 months can receive an early MMR dose before international travel (this early dose does not count toward the routine two-dose series, which is still given later), and children 12 months and older as well as adults should be up to date on two documented doses.

Prevention Summary

11. Recent Research and Advances

The most influential recent advance in measles science is the firm establishment of immune amnesia. The 2019 studies by Mina (in Science) and Petrova (in Science Immunology) used modern antibody-profiling and immune-repertoire sequencing to show, at a molecular level, that measles destroys a substantial portion of pre-existing immune memory — reframing measles from a self-limited rash illness into a cause of prolonged, broad immune suppression. This has strengthened the public-health case for prevention: vaccination protects against not only measles but the years of heightened vulnerability to other infections that follow.

Other active areas include better understanding of SSPE, with research suggesting it may be more common after early-childhood infection than older estimates implied; ongoing refinement of vitamin A recommendations within their proper scope as a treatment adjunct; and global efforts to extend MMR coverage, develop more heat-stable formulations and microneedle-patch delivery to reach remote populations, and improve outbreak surveillance through viral genotyping. Across all of this work, the central message is unchanged: high two-dose vaccination coverage is the decisive tool against measles.

12. References & Research

Historical Background

Measles is an ancient scourge — distinct descriptions of the illness date back over a thousand years, and the Persian physician Rhazes (al-Razi) clearly distinguished measles from smallpox around the 10th century. In 1954, John Enders and Thomas Peebles isolated the measles virus in cell culture, work that built on Enders' Nobel-winning poliovirus culture methods and opened the door to a vaccine. The first measles vaccine was licensed in 1963, and improved attenuated versions followed; combined with mumps and rubella, it became the MMR vaccine. Widespread vaccination drove US cases down by more than 99%, culminating in the declaration of measles elimination from the United States in 2000. Most recently, the 2019 discovery of immune amnesia transformed the scientific understanding of just how much harm measles does, reinforcing the value of prevention.

Key Research Papers

  1. Guerra FM, Bolotin S, Lim G, et al. The basic reproduction number (R0) of measles: a systematic review. The Lancet Infectious Diseases. 2017;17(12):e420–e428.
  2. Strebel PM, Orenstein WA. Measles. New England Journal of Medicine. 2019;381(4):349–357.
  3. Rota PA, Moss WJ, Takeda M, et al. Measles. The Lancet (Seminar). 2017.
  4. Mina MJ, Kula T, Leng Y, et al. Measles virus infection diminishes preexisting antibodies that offer protection from other pathogens. Science. 2019;366(6465):599–606.
  5. Petrova VN, Sawatsky B, Han AX, et al. Incomplete genetic reconstitution of B cell pools contributes to prolonged immunosuppression after measles. Science Immunology. 2019;4(41):eaay6125.
  6. Mina MJ, Metcalf CJE, de Swart RL, et al. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science. 2015;348(6235):694–699.
  7. Hussey GD, Klein M. A randomized, controlled trial of vitamin A in children with severe measles. New England Journal of Medicine. 1990;323(3):160–164.
  8. Imdad A, Mayo-Wilson E, Herzer K, Bhutta ZA. Vitamin A supplementation for preventing morbidity and mortality in children from six months to five years of age. Cochrane Database of Systematic Reviews. 2017;3:CD008524.
  9. Wendorf KA, Winter K, Zipprich J, et al. Subacute sclerosing panencephalitis: the devastating measles complication that might be more common than previously estimated. Clinical Infectious Diseases. 2017;65(2):226–232.
  10. Madsen KM, Hviid A, Vestergaard M, et al. A population-based study of measles, mumps, and rubella vaccination and autism. New England Journal of Medicine. 2002;347(19):1477–1482.
  11. Hviid A, Hansen JV, Frisch M, Melbye M. Measles, mumps, rubella vaccination and autism: a nationwide cohort study. Annals of Internal Medicine. 2019;170(8):513–520.
  12. Taylor B, Miller E, Farrington CP, et al. Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association. The Lancet. 1999;353(9169):2026–2029.
  13. Jain A, Marshall J, Buikema A, et al. Autism occurrence by MMR vaccine status among US children with older siblings with and without autism. JAMA. 2015;313(15):1534–1540.
  14. The Editors of The Lancet. Retraction—Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. The Lancet. 2010;375(9713):445.

Research Papers

The links below run live searches on PubMed, the US National Library of Medicine's database of biomedical literature. Use them to explore current and historical research on measles and its prevention.

  1. Measles virus transmission
  2. Measles immune amnesia
  3. MMR vaccine effectiveness
  4. MMR vaccine safety and autism
  5. Measles complications and pneumonia
  6. Subacute sclerosing panencephalitis
  7. Vitamin A in measles treatment
  8. Measles herd immunity threshold
  9. Measles outbreaks and vaccination coverage
  10. Measles in pregnancy
  11. Measles post-exposure prophylaxis
  12. Measles encephalitis

Connections

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