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Measles is caused by a virus, morbillivirus, that’s spread primarily via coughing and sneezing, and is recognizable by its well-known rash, which spreads to cover most of the body. The virus is extremely contagious: on average, 90% of those exposed to someone with the measles will get the disease themselves unless they’ve been vaccinated, or have had measles before. Patients who survive a case of the measles retain immunity to it for life.

Although measles has no treatment or cure, most people who catch it do survive the infection. However, the majority of measles patients will feel extremely sick for approximately one week, and up to 30% will suffer some sort of complication to the disease, ranging from diarrhea, ear infections, or pneumonia to seizures or hearing loss as a result of swelling in the brain. In some areas of the world without widespread access to medical care, up to 5% of children die of the measles.

In the decade prior to the introduction of the MMR (measles-mumps-rubella) combination vaccine in the United States, it’s estimated that more than three million people were infected with the measles each year. Since MMR reached widespread use, measles cases in the country have been reduced by more than 99%.[1]

In the United States, ongoing measles transmission was declared eliminated in 2000. Cases are still imported, however, via travelers from foreign countries. According to the Centers for Disease Control, about 50% of imported measles cases in the United States are in U.S. residents coming back from other countries. U.S. residents traveling outside the United States are encouraged to verify that they are immune to measles, either via previous infection or vaccination, before traveling.