context: The MMR vaccine protects against measles, mumps, and rubella ( German measles). Many children in the U. S. are immunized as infants and toddlers, but that doesn't guarantee lifetime protection. And not everyone gets vaccinated as a child. Many adults move to the U. S. from countries without immunization programs. World travel increases the chances of these diseases spreading. Generally, adults born before 1957 are considered immune to measles and mumps. The CDC advises most adults born in 1957 or afterward who can't show that they've had all 3 diseases get an MMR vaccine, whether they had one as a child or not. The three diseases covered by the MMR vaccine -- measles, mumps, and rubella -- are highly contagious. Viruses cause all three of these illnesses, and they spread through the air. They can pass from person to person through coughing, sneezing, or just breathing. Measles. This disease causes a fever, runny nose, and rash. It attacks the throat and lungs. Vaccinations have helped stop the spread of the disease in the U. S., but there are still cases reported. While immunization rates are on the rise around the world, the World Health Organization ( WHO) estimates there were 89,780 deaths from measles in 2016. Measles outbreaks often happen in countries without strong childhood immunization programs. But outbreaks have also happened in Europe, South Africa, and the Philippines. Mumps. This disease causes fever, fatigue, head and muscle aches, and swelling of the salivary glands. In men, it can cause the testicles to become inflamed. Mumps can lead to a loss of hearing, infection of the covering around the brain and spinal cord, and other serious problems. Mumps outbreaks do still happen in the U. S., but rarely. Rubella ( German measles). This disease can cause a fever and rash. It's especially dangerous if a pregnant mother has it. Rubella can lead to serious birth defects, including heart problems, deafness, liver and spleen damage, and intellectual disability. If a woman has rubella while pregnant, there's at least a 20% chance her baby will have problems. The CDC says most adults born in 1957 or later should get at least one dose of the MMR vaccine. Because of the risk of birth defects, all women of childbearing age should have the MMR vaccine unless they're pregnant or have proof of immunity, or proof of already being vaccinated for rubella. The CDC says adults at greater risk of measles or mumps should get two doses of MMR vaccine, the second one 4 weeks after the first. This includes adults who: Have been exposed to measles or mumps or live in an area where an outbreak has happened Are students in colleges or trade schools Travel internationally Work in health care For measles, the CDC advises a second dose for adults who: Were previously given a vaccine made with "killed" measles (instead of the live-type of vaccine used today) Were given an MMR vaccine between 1963 and 1967, but there's no record of what type. Adults don't need the MMR vaccine if: They have proof of vaccination already. They have proof that they've already had measles or mumps and rubella. Adults who should not have the MMR vaccine include people in these groups: Pregnancy. Pregnant women should not get the MMR vaccine due to risks to the baby. Women who get the MMR vaccine should wait 4 weeks before getting pregnant. Life-threatening allergic reactions. Adults who have had a life-threatening allergic reaction to gelatin, a previous MMR vaccine, or a medication called neomycin should not get the vaccine. Medical conditions. Adults should talk with their doctor if they: Have HIV Have any other immune system disorder Have cancer or are being given cancer drugs or X-rays Are taking steroids or other drugs that affect the immune system Have had a low platelet count (a blood disorder) Have had a blood transfusion or took blood products Have a moderate or severe illness As with many vaccines, the MMR vaccine works with the immune system to build up protection by putting a small amount of the virus into the body. The safest and most effective ingredients in the MMR vaccine used today include "attenuated" forms of each virus, which means they're live forms of the virus that have been made weak in medical labs. For most adults, the benefits of the MMR vaccine outweigh the risks. A few people develop a short-term mild rash, fever, swollen glands, or pain and stiffness in the joints after getting the shot. More serious, and rare, side effects include a temporary low platelet count or serious allergic reaction. Call your doctor if you have trouble breathing, dizziness, rapid heartbeat, hives, weakness, or other problems after vaccination.