Vaccines are one of the greatest medical discoveries in history. Thanks to vaccines, diseases like polio, measles, whooping cough, meningitis and chicken pox have been greatly reduced, and other deadly diseases have been eradicated.

Measles, in particular, is common in other parts of the world and can spread easily to the unvaccinated in America. It is extremely contagious, infecting nearly 90 percent of unvaccinated people who come into contact with it. 

The MMR (measles, mumps and rubella) vaccine is a safe and effective way to prevent the spread of the virus. Here’s who should get vaccinated:

• Children. The CDC recommends two doses of the MMR vaccine in childhood: the first dose between 12 and 15 months and the second at four to six years.
• Teens and young adults. For unvaccinated individuals, two doses of the MMR vaccine are recommended for individuals in this age group: The first dose is given and then followed with a second dose a minimum of 28 days after the first.

Here, our experts in Infectious Disease answer frequently asked questions about measles:

Q: How effective is the measles vaccine?
A: The measles vaccine is very effective. One dose of measles vaccine is about 93% effective at preventing measles if exposed to the virus and two doses is about 97% effective.

Q: Could I still get measles if I am fully vaccinated?
A: Very few people—about three out of 100—who get two doses of measles vaccine will still get measles if exposed to the virus. Experts aren’t sure why; it could be that their immune systems didn’t respond as well as they should have to the vaccine. But the good news is, fully vaccinated people who get measles are much more likely to have a milder illness, and they are also less likely to spread the disease to other people, including people who can’t get vaccinated because they are too young or have weakened immune systems.

Q: Do I ever need a booster vaccine?
A: Generally speaking, no. People who received two doses of measles vaccine as children, according to the U.S. vaccination schedule, are considered protected for life and do not need a booster dose.

Adults who were not vaccinated as children need at least one dose of measles vaccine unless they have evidence of immunity.  Adults who are going to be in a setting that poses a high risk for measles transmission, including students at post-high school educational institutions, healthcare personnel, and international travelers, should make sure they have had two doses separated by at least 28 days.

Q: Am I protected against measles?
A: You are considered protected from measles if you have evidence (medical records) showing any of the following.

• If you were born before 1957.
• If you had ever had confirmed measles in the past.
• If you have a laboratory-confirmed immunity (titer) against measles
• If you had two doses of measles-containing vaccine (e.g. MMR), and you are:  
  • A school-aged child (grades K-12)
  • An adult without prior vaccination or disease history and in a setting that poses a high risk for measles transmission (e.g. colleges, healthcare or international travelers).
• If you had one dose of measles-containing vaccine (e.g. MMR), and you are:  
  • A preschool-aged child
  • An adult without prior vaccination or disease history and not in a high-risk setting for measles transmission.

Q: What should I do if I am unsure about my immunity to measles?
A: If you are unsure, you should first try to find vaccination records or documentation of measles immunity. If written documentation of measles immunity is not available, you should get vaccinated with measles-mumps-rubella (MMR) vaccine. Another option is to get a blood test to determine immune status. There is no harm in getting another dose of MMR vaccine if you may already be immune to measles (or mumps or rubella).

Q: Should we vaccinate children under 1 year of age?
A: The local and state health departments have not yet recommended vaccination of this age group.  We anticipate further guidance as to what will be defined as a threshold number of cases that would warrant vaccinating children aged 6-11 months.

Q: What should I do if I suspect I may have measles?
A: If you have symptoms that resemble measles, please call your primary care physician first or the county Department of Health who will help you determine the likelihood of infection and further advise you.

Q: What are some symptoms of suspected measles?
A:  Measles is typically characterized by:

• Generalized, maculopapular rash – flat, red area covered with small bumps - lasting greater than 3 days; AND
• Temperature greater than 101°F or 38.3°C; AND
• At least one of the following: Cough, runny nose, or conjunctivitis