Some adults may need a measles booster shot. Who should get one and why?

Measles, once considered eliminated in the United States, has been making an unfortunate comeback. With recent outbreaks in various states, health experts are urging some adults to check their vaccination status. While most people are protected, some may need a booster shot to ensure they remain immune.

What to know about measles

Measles, also called rubeola, is a highly contagious viral infection that spreads through respiratory droplets when an infected person coughs or sneezes. The virus can linger in the air and on surfaces for hours, making it easy to catch if you're not immune.

Symptoms typically appear 10 to 14 days after exposure and include:

• high fever
• cough
• runny nose
• red, watery eyes
• small, white bumps on the inside of the mouth
• measles rash: flat red spots, sometimes with small raised bumps on top. Rash typically starts on the face and spreads downward, across the arms, trunk, legs, and feet.

Measles can lead to serious complications, including pneumonia, brain swelling (encephalitis), blindness, hearing loss, and even death, particularly in young children, pregnant women, and people with weakened immune systems.

"We worry about the outbreaks because measles is a highly contagious infection," explains Dr. Michelle Chan, an infectious disease physician at Beth Israel Deaconess Medical Center and an instructor in medicine at Harvard Medical School. "Individuals who have not been immunized, children too young for the vaccine, and those who are immunocompromised can become very ill from measles."

The best way to prevent measles is through vaccination. Prior to the introduction of widespread vaccination programs, measles was responsible for approximately 2.6 million deaths worldwide.

In the United States and other developed nations, the initial vaccine is administered between 12 and 15 months of age, followed by a second dose at 4 to 5 years old. Overall, the vaccine has a strong safety profile. Side effects are mostly mild, and the vaccine has no link to autism.

Could you benefit from a measles booster shot?

The measles vaccine, given as part of the measles-mumps-rubella (MMR) shot, provides long-term immunity. A single dose of the MMR vaccine is 93% effective at preventing illness, while two doses increase effectiveness to 97%. However, not everyone has the same level of protection.

For example, prior to 1989, one dose of the MMR vaccine was standard, so most people born before 1989 likely received only one dose. According to Dr. Chan, "One dose of the MMR vaccine is highly effective, but certain populations who are at high risk of exposure — such as health care workers, international travelers, and close contacts of immunocompromised individuals — may want to be proactive about ensuring they've received the full series of vaccinations."

In addition, individuals vaccinated between 1963 and 1967 may have received a less effective, inactivated (killed) version of the measles vaccine. "Anyone who received the inactivated vaccine or is unsure of the type they received should get one to two doses of the MMR vaccine," Dr. Chan advises.

If you're not sure of your immunization history and your medical records are unclear, getting an extra dose of the MMR vaccine is a safe and effective option. "If you are unsure, you can choose to take a dose of the vaccine. It is very safe and not harmful if you happen to receive an additional dose," Dr. Chan reassures.

Because of the high rates of measles in the U.S. prior to 1957, anyone born before 1957 is presumed to have had measles or been exposed to the virus and, as a result, does not need a measles vaccine or booster shot.

Who should consider a measles booster and why?

The Centers for Disease Control and Prevention (CDC) recommends that certain adults check their measles immunity and get a booster shot if necessary. You may need a booster if:

• You received the inactive measles vaccine between 1963 and 1967. This version was not fully effective, so you may not be protected.
• You work in health care or a setting with high exposure risk and have had only one dose of the measles vaccine. Working in a hospital, school, or child care center can increase the chance of exposure to measles.
• You are unsure of your vaccination status. If you don't have documentation or a history of measles infection, you may opt to get a dose of the MMR vaccine.
• You are traveling internationally. Some countries still have high measles rates, and travelers are at risk of bringing the virus back home.

If you fall into one of these higher-risk groups, check your vaccination status and speak with your doctor about a measles vaccine booster.

"It all comes back to vaccines — this is our most effective method of preventing measles infection and resurgence," Dr. Chan emphasizes.