Thanks to vaccines, we no longer have to worry about many dangerous diseases. Measles—once a common, often lethal illness—is now quite rare, and is often relegated to that “no worry” list.

However, when cases of measles occur, they are dangerous, particularly for children under the age of 5. That’s because measles is one of the world’s most contagious diseases. It is spread through the air (when an infected person coughs or sneezes) or by direct contact with a contaminated surface.

Measles is also dangerous because of the complications that can arise in affected people, especially in children who are malnourished or have weakened immune systems. In the United States, measles is fatal for about 2 in 1,000 children infected. Between 2000 and 2018, measles vaccinations prevented an estimated 23.2 million deaths worldwide.

For this reason, doctors emphasize the importance of vaccinating children with the measles-mumps-rubella (MMR) vaccine. (Adults should receive at least one dose of the MMR vaccine if they have never received it or have never had measles.) It’s also wise to educate yourself about this virus, which infects the respiratory tract and then spreads throughout the entire body.

Since the MMR vaccine began to be used routinely in the U.S. in 1963, the number of measles cases has dropped dramatically. But in recent years, there have been outbreaks around the country. These typically occurred (and spread) because of an increase in unvaccinated travelers who brought the virus to the U.S. from a country where measles is more common; children in the U.S. who do not receive the vaccine are more vulnerable to the virus.

At Yale Medicine, we have a team of pediatric and adult infectious disease specialists who are well versed in the prevention and treatment of measles and other diseases. Our general pediatricians and primary care providers are committed to educating the public about vaccination recommendations. 

Measles, mumps, and rubella are all viral, contagious diseases that can be prevented by a single vaccination (known as the MMR vaccine).

Here are some details about the three diseases:

• Measles: This infection, caused by the rubeola virus (which is not the same as rubella, described below), causes a fever, rash, cough, runny nose, and red eyes. Ear infection, diarrhea, pneumonia and—in rare cases—brain damage, and even death can occur. The MMR vaccine is 97 percent effective at preventing measles. 

• Mumps: This disease typically starts with a few days of fever, headache, muscle aches, and fatigue, followed by swollen salivary glands. Even though the MMR vaccine has significantly reduced the number of mumps cases in the U.S. each year, it can crop up in places where people have prolonged, close contact with an infected person. For example, it can spread through sports teams, dormitories, or classrooms. Though rare, complications can include swelling of the testicles or ovaries, deafness, inflammation of the brain and/or tissue covering the brain and spinal cord (encephalitis/meningitis). Mumps is rarely fatal. The MMR vaccine is 88 percent effective at preventing mumps.

• Rubella: This disease, often known as “German measles,” causes fever, sore throat, rash, headache, and red, itchy eyes. The infection is particularly dangerous to pregnant women, as it can lead to serious birth defects or miscarriage. The MMR vaccine is 97 percent effective at preventing rubella.

“Measles is its own viral illness and is quite different from mumps and rubella,” explains Maryellen Flaherty-Hewitt, MD, a Yale Medicine pediatrician. “Some countries give out separate vaccines for each of these viruses, but the U.S. is fortunate enough to have the combination vaccine, which is quite effective and spares our children multiple shots.” 

A high fever is usually the first sign of measles, and it typically starts 10 to 12 days after exposure to the virus. The fever usually lasts four to seven days.

Other symptoms that occur in the initial stage of infection include cough, runny nose, and red and watery eyes. Small white spots may also develop inside the cheeks. The rash typically erupts next (about 14 days after virus exposure), usually starting on the face and upper body and then spreading to the trunk, hands, and feet. The rash stays for about six days and then begins to fade.

A very contagious virus, measles lives in mucus in the nose and throat of an infected person. Spread through coughing and sneezing, it can live for up to two hours in the air of a room. If someone breathes the infected air or touches a contaminated surface (and then touches their own eyes, nose, or mouth), they can catch the virus.

Measles is so contagious, in fact, that if one person in a room has measles, 90 percent of the (unvaccinated or unprotected, by not having had the measles previously) people nearby will become infected. An infected person can transmit the disease four days before and four days after the onset of the characteristic rash that accompanies the virus. 

A doctor will suspect measles based on the common symptoms including fever and rash, and especially if the patient has recently traveled internationally or was exposed to someone with a fever and a rash. Laboratory blood and tissue tests (from a throat or nose swab) can confirm the diagnosis. A urine sample may also show evidence of the virus. 

While measles can be serious in all age groups, complications from the disease occur most often in children under the age of 5 and adults over the age of 20. The disease is often accompanied by ear infections and diarrhea.

Severe complications are more likely to occur in children who are poorly nourished, have a weakened immune system from leukemia and HIV, or are affected by other serious diseases. The most serious potential complications include blindness, brain swelling (encephalitis), respiratory infections such as pneumonia, and, in rare cases, death.

Young children who are not yet vaccinated against measles are at the highest risk of developing measles and complications of the virus. Unvaccinated adults (or those who don’t have natural immunity from having had measles), including pregnant women, are also at risk.

Children under the age of 12 months, born to women who have either had measles or been vaccinated, are offered some protection from the disease because of antibodies passed from mother to baby, according to the CDC. Interestingly though, those passed-on antibodies can make the MMR vaccine less effective, which is why the first dose is not given until a child turns 1.  

There is no specific antiviral treatment for measles. Care for a person with measles should include resting, eating well, and drinking plenty of fluids (to prevent dehydration caused by diarrhea). Fever-reducing medications (acetaminophen or ibuprofen) may be given for comfort, and antibiotics may be needed to treat ear or eye infections, or pneumonia, all of which can develop as a result of the infection. 

Children who are diagnosed with measles should receive two doses of vitamin A supplements, likely administered by their physician, spaced 24 hours apart. 

Administering the MMR vaccine to children around their first birthday is key to prevention, which is why large immunization campaigns in countries with high cases of measles are so vital. The measles vaccine has been deemed safe and effective by the World Health Organization and the CDC, and has been in use for more than 50 years. 

In the U.S., the CDC recommends all children receive two doses of the MMR vaccine. The first dose should be administered between ages 12 and 15 months, and the second dose between ages 4 and 6 years. Today, children are often also vaccinated against chicken pox (varicella) at the same time; the vaccine they receive is called MMRV. 

Adults who have not had the vaccine or the virus—or aren’t sure of either—can have their immunity checked by a laboratory blood test. If they are not immune, they should get at least one dose of the MMR vaccine.

If you have received the recommended two doses of the MMR vaccine during childhood, in accordance with the U.S. vaccination schedule, you can consider yourself protected for life, the CDC says. Two doses of the MMR vaccine are 97 percent effective against measles. (About 3 out of every 100 people who receive two doses of the MMR vaccine will get measles if exposed to the virus, but they will have a milder course, and are less likely to spread measles to others.)

If you are unvaccinated and exposed to the virus, you can receive the vaccine and be protected within three days of exposure, meaning the vaccine will stop the virus in its tracks. Those who should not receive the vaccine (pregnant women, people with certain cancers or untreated tuberculosis, and those with serious illnesses or weakened immune systems) instead are given immune globulin (a therapy made from human plasma) to strengthen their immune response and lower the risk that complications will develop. 

Like any medication, the MMR vaccine can have side effects, including a sore arm from the injection, fever, mild rash, and temporary joint pain or stiffness. The MMR vaccine has been linked to a small risk of febrile seizure (convulsions caused by a fever, not the vaccine). Febrile seizures in general are rare, especially following MMR vaccination, and do not pose any long-term harm.

In extremely rare cases, people have serious allergic reactions to the vaccine. Those who have had a life-threatening allergic reaction to a dose of the MMR vaccine or a severe allergy to any part of the vaccine may be advised to not receive it. Talk to your physician if you have concerns. 

There is no federal law that requires children entering childcare or public schools to receive certain vaccinations, but each state has its own laws. In some cases, religious and philosophical exemptions are allowed.

“There are medical exemptions to any vaccine that would include a life-threatening allergic reaction to the vaccine or any component of the vaccine,” Dr. Flaherty-Hewitt explains. “But this is rare. It was once thought that reactions to the MMR vaccine had to do with the trace quantities of egg protein used in development of the vaccine, but this is no longer thought to be the case and children with egg allergies get the MMR vaccine.” 

At Yale Medicine, our pediatric and adult infectious disease specialists are experts in studying and treating viral, bacterial, and parasitic infections. We work closely with community physicians to advocate for adhering to vaccination schedules that can prevent highly contagious diseases, including measles. In the event that an outbreak occurs, we work closely with physicians from other specialties to treat any complications from the disease.