Vaccination is the only reliable way to prevent measles
The measles vaccine (MMR) stops measles before it starts. Two doses of the MMR vaccine are about 97% effective at preventing measles infection. One dose is roughly 93% effective. If you have not had two doses or a documented case of measles, you are not protected.
The vaccine protects you by training your immune system to recognize and fight the measles virus. It does not work after you have already caught measles—vaccination must happen before exposure. Most people receive their first MMR dose at 12 to 15 months old and their second dose at 4 to 6 years old, but adults without immunity can receive both doses at any time.
If you are unsure whether you have been vaccinated, a blood test can check your immunity level. This test, called a titer, shows whether your body has antibodies against measles. Many doctors can order this test, and some workplaces or schools require it before allowing unvaccinated people on site during an outbreak.
Key Takeaways
- Two MMR vaccine doses are the most effective way to prevent measles, and the vaccine works before infection, not after.
- Adults born in 1957 or later without documented measles immunity should get vaccinated, as older birth cohorts are assumed immune from natural infection.
- If you are exposed to measles and unvaccinated, the vaccine can prevent or reduce severity of illness if given within 72 hours of exposure.
- During measles outbreaks, unvaccinated people should avoid crowds, healthcare settings, and travel until immunity is confirmed.
- Measles spreads through the air when an infected person coughs or sneezes, so distance and masks offer temporary protection only if vaccination is not possible.
Who should get the MMR vaccine
Anyone born in 1957 or later without a documented measles case or two MMR doses should be vaccinated. People born before 1957 are generally considered immune from natural infection during childhood, when measles was common.
Certain groups should prioritize vaccination: healthcare workers, teachers, childcare staff, international travelers, and people living in or planning to visit areas with measles cases. Pregnant people cannot receive the MMR vaccine because it is a live vaccine, but they should be vaccinated before becoming pregnant if they lack immunity.
People with certain medical conditions—including HIV, cancer, or conditions treated with immunosuppressive drugs—may not be able to receive the live MMR vaccine. A doctor can determine whether the vaccine is safe for you based on your health history.
What to do if you have been exposed to measles
If you know you were near someone with measles and you are not vaccinated, contact your doctor immediately. The MMR vaccine can prevent measles or reduce how severe it becomes if given within 72 hours of exposure. After 72 hours, the vaccine is less likely to prevent infection, but your doctor may still recommend it.
If you cannot receive the vaccine—for example, because you are pregnant or immunocompromised—ask your doctor about immunoglobulin, a blood product that can reduce measles severity if given within six days of exposure. This is not a substitute for vaccination but may help if vaccination is not an option.
While waiting to see your doctor or after vaccination, stay home and away from other people, especially infants, pregnant people, and anyone with a weakened immune system. Measles spreads through the air when an infected person coughs or sneezes, so distance is important during the incubation period (the time before symptoms appear, usually 10 to 14 days).
Protecting others when you are unvaccinated
If you are unvaccinated and cannot be vaccinated for medical reasons, the best protection for others is distance. During measles outbreaks, avoid crowded places, public transportation, healthcare facilities, and schools. If you must be around others, wear a high-quality mask (N95 or equivalent) that covers your nose and mouth.
Tell people you spend time with regularly that you are unvaccinated. This allows them to decide whether to limit contact with you and gives them time to check their own immunity. If someone in your household gets measles, isolate from them as much as possible—use separate bathrooms if you can, and have them wear a mask if they must be in shared spaces.
Measles is highly contagious: one infected person typically spreads it to 12 to 18 unvaccinated people. Vaccination protects not just you but also people too young to be vaccinated, pregnant people, and people whose immune systems cannot fight the virus on their own.
Vaccination records and proof of immunity
Keep your vaccination records in a safe place. Your doctor's office, local health department, or school records can provide documentation of your MMR doses. Some states maintain immunization registries where you can request a record if you have lost your original paperwork.
If you need proof of immunity for work, travel, or school, you will need either documentation of two MMR doses or a positive antibody titer (blood test showing immunity). A single dose of the vaccine is not sufficient proof for most institutions; two doses are the standard requirement.
If you received the vaccine outside the United States, ask your doctor whether your vaccination meets U.S. standards. Some countries use different vaccine formulations or schedules, and your doctor can advise whether you need additional doses.
Measles outbreaks and community spread
Measles outbreaks occur when vaccination rates in a community drop below a certain threshold. Once measles appears in an area, it spreads rapidly among unvaccinated people. If an outbreak is reported in your region, check your vaccination status immediately and get vaccinated if you are not protected.
Public health departments track measles cases and post outbreak information on their websites. If you live in or travel to an area with confirmed cases, vaccination becomes urgent. Schools, workplaces, and healthcare facilities may require proof of immunity during an outbreak and may exclude unvaccinated people from attending.
Measles can spread before a person knows they have it—symptoms do not appear for 10 to 14 days after exposure, but the virus is contagious from four days before the rash appears until four days after it starts. This means unvaccinated people can unknowingly spread measles to others.
What vaccination does not do
The MMR vaccine does not prevent you from being around measles. It prevents measles infection itself. If you are vaccinated and exposed to measles, your immune system will recognize the virus and stop it before you get sick. You will not develop symptoms, and you will not spread measles to others.
The vaccine is not a treatment for measles once you have caught it. If you become infected despite vaccination (which is rare), your symptoms will likely be milder than in an unvaccinated person, but the vaccine cannot cure an active infection. This is why vaccination before exposure is essential.
Frequently Asked Questions
Can I get measles if I have been vaccinated?
Measles infection after two MMR doses is rare—about 3 in 100 vaccinated people may still get measles if exposed, and their illness is usually much milder. One dose offers less protection. If you have had two doses, you are considered immune for the purposes of public health and workplace requirements.
How long does immunity from the MMR vaccine last?
MMR immunity lasts a lifetime for most people who receive two doses. You do not need booster shots as an adult. A blood test can confirm immunity if you are unsure whether your vaccination worked.
Is it safe to get the MMR vaccine if I am an adult?
Yes. The MMR vaccine is safe for adults without immunity. Side effects are usually mild—soreness at the injection site, low fever, or a rash—and serious side effects are extremely rare. Your doctor can discuss any specific health concerns before vaccination.
What should I do if I think I have measles?
Call your doctor before going to the office or emergency room. Measles symptoms include high fever, cough, runny nose, and a rash that starts on the face and spreads downward. Tell your doctor you think you have measles so they can take precautions to protect other patients. Stay home and away from others until your doctor says it is safe.
Can I travel internationally without MMR vaccination?
Many countries require proof of MMR immunity for entry, especially if measles is circulating there. Check the requirements for your destination before traveling. If you are unvaccinated, you may be denied entry or required to be vaccinated at the border.