Measles is one of the most contagious viral infections known to humanity, capable of spreading through the air and remaining active in a room for hours after an infected person has left. Before widespread vaccination began in 1963, this highly infectious disease caused millions of deaths worldwide each year, mostly among young children. Today, despite the availability of a safe and effective vaccine, measles continues to threaten communities where vaccination rates have dropped, leading to dangerous outbreaks that can result in severe complications, permanent disability, and even death.

Understanding the Global Impact of Measles

The reach and severity of measles remain significant concerns for global health authorities. In 2023, an estimated 107,500 people died from measles worldwide, with the vast majority of these deaths occurring among children under five years of age who had not received adequate vaccination.^[3] This number represents a staggering toll, particularly when considering that a safe and cost-effective vaccine exists and has been available for decades.

Between 2000 and 2023, accelerated immunization efforts successfully prevented an estimated 60 million deaths from measles. This remarkable achievement demonstrates what is possible when communities prioritize vaccination.^[3] However, progress has not been uniform across all regions. Before the introduction of the measles vaccine in 1963, major epidemics occurred approximately every two to three years, causing an estimated 2.6 million deaths annually.^[3]

In the United States, measles was declared eliminated in 2000, meaning there was no continuous disease transmission for at least one year. The country achieved this milestone through high vaccination rates and strong public health infrastructure.^[6] However, elimination does not mean the disease has disappeared completely. As of May 2025, the United States has reported 935 confirmed cases across multiple states, representing the highest number of measles infections the country has seen in more than 30 years.^[6]

The COVID-19 pandemic created significant setbacks for measles prevention efforts. The suspension of immunization services and declining vaccination rates left millions of children vulnerable to preventable diseases like measles. The proportion of children receiving their first dose of measles vaccine dropped from 86% in 2019 to 83% in 2023, a decline that may seem small but represents millions of unprotected children globally.^[3]

What Causes Measles and How It Spreads

Measles is caused by the measles virus, also called morbillivirus, which is an enveloped, single-stranded virus that belongs to the paramyxovirus family.^[6] This virus is exceptionally efficient at spreading from person to person, making measles one of the most contagious diseases known to medical science.

The virus spreads primarily through the air when an infected person breathes, coughs, sneezes, or talks. These actions release tiny droplets containing the virus into the surrounding environment.^[3] What makes measles particularly dangerous from a transmission standpoint is that the virus can remain alive and contagious in the air or on surfaces for up to two hours after an infected person has left a room.^[4] This means that someone can become infected simply by entering a room where an infected person was present earlier, even if they never come into direct contact with that individual.

Direct contact with respiratory secretions, such as saliva, also transmits the virus. Sharing food or drinks, kissing, shaking hands, or hugging someone with measles can spread the infection. Additionally, touching a surface or object contaminated with the virus and then touching your mouth, nose, or eyes can lead to infection.^[9]

The contagious period for measles is particularly concerning. An infected person can spread the virus to others from approximately four days before the characteristic rash appears until about four days after the rash develops.^[1] This means that individuals are contagious before they even know they have measles, making it extremely difficult to prevent transmission without high community vaccination rates.

Measles can also be transmitted from a pregnant woman to her fetus during pregnancy, a condition known as vertical transmission. When this occurs, it can result in congenital measles, which is characterized by a febrile rash syndrome appearing within the first 10 days of the newborn’s life. Congenital measles can lead to severe complications including brain inflammation and death, and carries a higher risk of developing a rare but fatal condition years later.^[1]

Risk Factors for Measles Infection

The single most important risk factor for contracting measles is lack of vaccination. Anyone who has not been protected against measles through vaccination or previous infection is at risk of getting the disease.^[4] In the recent outbreaks across the United States, approximately 92% of confirmed cases involved people who were either known to be unvaccinated or had unknown vaccination status. Only about 4% of cases occurred in people who had received both recommended doses of vaccine.^[5]

Infants younger than 12 months old face particularly high risk because the first dose of the measles vaccine is typically not given until children are between 12 and 15 months of age. Newborns may receive some temporary protection from antibodies passed from their mother during pregnancy, but this protection usually lasts only about six months. Infants aged 6 to 11 months have very little protection against measles and are highly vulnerable to infection.^[5]

International travel significantly increases measles risk. Although measles has been eliminated from the United States, it remains common in many parts of the world. Every year, measles is brought into the United States by unvaccinated travelers who contract the disease while visiting other countries. These travelers may be Americans returning home or international visitors, and they can then spread the disease to unvaccinated people in their communities.^[4]

Living in or traveling to areas with low vaccination rates creates heightened risk. Communities where immunization rates fall below 95% provide an environment where the measles virus can circulate more easily, increasing the likelihood of outbreaks. When vaccination rates in a community drop, even vaccinated individuals face increased exposure risk, though they remain much better protected than those who are unvaccinated.^[3]

Healthcare workers who have not been vaccinated face occupational exposure risk. Because they regularly encounter sick patients, healthcare personnel who lack immunity to measles may become infected and potentially spread the disease to vulnerable patients. For this reason, healthcare workers are specifically recommended to have documentation of two doses of measles vaccine separated by at least 28 days.^[15]

Recognizing the Symptoms of Measles

Measles symptoms typically appear 7 to 14 days after a person has been exposed to the virus. This period between exposure and symptom onset is called the incubation period.^[2] The disease does not announce itself all at once; instead, symptoms develop in stages, making early recognition challenging.

The first symptoms to appear are often mistaken for a common cold or flu. These initial signs include a high fever that may spike as high as 104 to 105 degrees Fahrenheit, a dry cough, runny nose (called coryza in medical terms), and red, watering eyes known as conjunctivitis.^[1] The combination of cough, coryza, and conjunctivitis is sometimes referred to as the “three Cs” of measles. Patients may also experience body aches, fatigue, sore throat, muscle pain, and headache during this early phase.^[9]

About two to three days after these initial symptoms begin, tiny white spots with blue-white centers may appear inside the mouth on the inner lining of the cheeks. These distinctive spots are called Koplik spots and are considered a hallmark sign of measles.^[2] However, they can be easily missed during examination and do not appear in every case. These spots typically fade when the characteristic rash begins to appear.^[9]

The measles rash usually appears about 14 days after exposure to the virus, or approximately three to five days after the initial symptoms begin.^[1] The rash consists of large, flat spots and small raised bumps that create a distinctive appearance. It typically starts on the face, often beginning near the hairline or behind the ears, then spreads downward across the body in a predictable pattern: from the head to the neck, then to the trunk (chest and back), and finally to the arms, legs, and feet.^[1]

On lighter skin, the measles rash appears bright red. On darker skin tones, it may appear purple or darker than the surrounding skin, or it might be more difficult to see. The spots may blend together as they spread across the body, creating areas of confluent rash. Unlike some other rashes, the measles rash typically does not itch.^[9] When the rash appears, fever often spikes even higher, sometimes reaching 105 degrees Fahrenheit or more.

It’s important to note that some people with weakened immune systems may not develop the characteristic rash, making diagnosis more challenging in these individuals.^[1] Additionally, digestive symptoms such as diarrhea, stomach pain, and vomiting may occur during the course of the illness.^[9]

Preventing Measles Through Vaccination

Vaccination represents the single most effective strategy for preventing measles. The measles vaccine is typically given as part of a combination vaccine called MMR, which protects against measles, mumps, and rubella, or MMRV, which also includes protection against varicella (chickenpox).^[5]

The standard vaccination schedule recommends two doses of MMR vaccine. The first dose is given when children are between 12 and 15 months of age, and the second dose is administered between ages 4 and 6 years, often just before children start kindergarten.^[5] This two-dose schedule provides excellent protection: one dose of MMR vaccine is approximately 93% effective at preventing measles, while two doses are about 97% effective.^[4]

For most adults born during or after 1957, at least one dose of measles vaccine is sufficient to be considered protected. However, certain groups of adults are recommended to have documentation of two lifetime doses separated by at least 28 days. These groups include students at post-high school educational institutions, healthcare personnel, international travelers, adults who live with people who have weakened immune systems, adults living with HIV who are able to receive the vaccine, and people whom public health authorities determine are at increased risk during an outbreak.^[15]

People born before 1957 are generally considered immune to measles because they likely contracted the disease during childhood when it was widespread. However, if these individuals are healthcare workers or will be in other high-risk situations, getting vaccinated may still be recommended.^[15]

For people who received two doses of measles vaccine according to the recommended schedule, no booster dose is needed. The protection from two properly spaced doses of MMR vaccine is considered lifelong, and there is no evidence that immunity wanes over time in people who respond appropriately to vaccination.^[15]

Special considerations apply for international travelers. Because measles remains common in many parts of the world, the CDC recommends that infants as young as 6 to 11 months receive an early dose of MMR vaccine if they will be traveling internationally. This early dose does not count as part of the routine two-dose series, so these children will still need two additional doses later, with the first given at 12 to 15 months and the second at 4 to 6 years.^[15]

If someone is exposed to measles and has not been vaccinated, post-exposure prophylaxis may be effective if given quickly. For people older than 6 months who are exposed to measles and are not immune, getting the MMR vaccine within three days of exposure may prevent the disease or make it less severe. After receiving post-exposure vaccination, individuals do not need to quarantine at home.^[8]

For infants younger than 12 months who are exposed to measles and are not immune, a treatment called immune globulin may be given within six days of exposure. This treatment provides antibodies that help the body fight the infection. After receiving immune globulin, individuals need to stay home in quarantine for 21 days.^[8]

How Measles Affects the Body

Measles is an acute viral respiratory illness that causes significant changes in how the body normally functions. Understanding these changes helps explain why measles can be so dangerous and why some people develop serious complications.

The measles virus initially infects the respiratory tract when virus-containing droplets are inhaled or come into contact with the mucous membranes of the nose, mouth, or eyes. Once inside the body, the virus begins replicating in the respiratory tract and then spreads throughout the entire body via the bloodstream, a process called viremia.^[3] This widespread distribution of the virus explains why measles causes symptoms affecting multiple organ systems, not just the respiratory system.

The characteristic rash of measles results from the body’s immune response to the virus. As immune cells work to eliminate infected cells in small blood vessels beneath the skin, inflammation occurs, creating the visible red or purple spots. This process spreads from the head downward as the immune response progresses throughout the body.^[1]

One of measles’ most devastating effects is what scientists call “immune amnesia” or immune system erasure. Unlike most other viral infections, measles has the unique and dangerous ability to reset a person’s immune system by erasing its memory of other pathogens it has encountered before. This means that any immunity gained from previous vaccinations or past infections with other diseases can be wiped out. After recovering from measles, a person will have strong immunity to measles itself, but may have lost protection against other infections they were previously immune to. This effect can last for two to three years.^[5]

Research has demonstrated that measles-related immune amnesia is a major contributing factor to deaths from other infectious diseases in the years following a measles infection. Children who survive measles become more vulnerable to other infections they would have previously been able to fight off, leading to increased illness and mortality even after the measles infection has resolved.^[5]

The virus can also directly damage various organs and tissues. In the respiratory system, measles causes inflammation of the airways, leading to the characteristic cough. The virus can damage the lining of the airways, making them more susceptible to secondary bacterial infections that cause pneumonia. In fact, pneumonia is the leading cause of measles-related death, particularly in young children.^[1]

In some cases, measles virus can invade the central nervous system, causing inflammation of the brain called encephalitis. This occurs in approximately 1 out of every 1,000 measles cases and often results in permanent brain damage. Brain inflammation can cause seizures, loss of consciousness, intellectual disability, and other neurological problems.^[1]

A rare but inevitably fatal complication called subacute sclerosing panencephalitis, or SSPE, represents one of measles’ most tragic long-term effects. This degenerative disease of the central nervous system typically develops 7 to 10 years after a person recovers from measles. It begins with subtle behavioral and intellectual changes, then progresses to seizures and eventually death. There is no effective treatment for SSPE.^[1] Children who develop congenital measles (infection acquired before birth) face an even higher risk of eventually developing SSPE.^[1]

Understanding Measles Complications

Although many people think of measles as just a rash and fever, the disease can cause serious and sometimes life-threatening complications. Even in previously healthy children, measles can result in severe illness requiring hospitalization.^[1]

Common complications occur frequently enough that they should be anticipated in measles cases. Ear infections, medically called otitis media, develop in about 1 in 10 children with measles. Diarrhea, which can lead to dehydration, affects fewer than 1 in 10 cases but can be severe, especially in young children.^[5] Inflammation of the voice box and windpipe, called laryngotracheobronchitis or croup, causes a characteristic barking cough and difficulty breathing.^[1]

Pneumonia represents one of the most serious common complications, occurring in approximately 1 in 20 people with measles. The pneumonia may be caused directly by the measles virus or by secondary bacterial infections that take advantage of the weakened respiratory system. Pneumonia is the leading cause of death from measles, particularly among young children.^[1]

Measles infection can be further complicated by secondary bacterial infections. The virus damages the lining of the respiratory tract and weakens the immune system, creating opportunities for bacteria to cause additional infections. These secondary infections can result in tonsillitis, ear infections, or bacterial pneumonia, requiring antibiotic treatment.^[1]

Serious but less common complications include brain inflammation (encephalitis), which develops in about 1 in 1,000 measles cases. Encephalitis often results in permanent neurological damage, including seizure disorders, hearing loss, intellectual disability, or other brain injuries. Between 1 and 3 out of every 1,000 children who become infected with measles will die from respiratory and neurologic complications.^[1]

Measles can also cause eye damage and, in some cases, lead to blindness. The virus can cause inflammation of various parts of the eye, and secondary infections can worsen eye damage. Dehydration from high fever and diarrhea can become severe enough to require intravenous fluid replacement.^[9]

Certain groups face higher risk for developing severe complications. Infants and children younger than 5 years old, adults older than 20 years, pregnant women, and people with weakened immune systems from conditions such as leukemia, HIV infection, or immunosuppressive medications are all at increased risk.^[1]

Pregnant women who develop measles face particular dangers. The infection can result in adverse outcomes for the pregnant woman herself, including severe pneumonia and death. Measles during pregnancy can also lead to pregnancy loss, premature delivery, and babies born with low birth weight. When measles is transmitted to the fetus during pregnancy, the resulting congenital measles can cause severe complications in the newborn, including encephalitis and death.^[1]

For malnourished individuals, particularly children in resource-limited settings, vitamin A deficiency can worsen measles complications. These patients are at higher risk for severe disease, eye damage, and death. Vitamin A supplementation given under medical supervision can help limit eye damage and reduce the severity of illness, though it does not prevent measles and is not a substitute for vaccination.^[5]