Should You Get a Measles Vaccine Booster?

[Originally published: March 11, 2025. Updated: Dec. 18, 2025]

These days, most people are vaccinated against measles, a highly contagious, life-threatening respiratory virus, when they are children. But the spread of measles cases throughout the United States in the past year is prompting some adults to wonder whether they need a measles booster shot.

Rising infections in 2025 were significant enough to put the U.S. at risk of losing its status as a country where measles is eliminated. The vast majority of those infections were in people who were either not vaccinated or their vaccination status was unknown.

“The problem with measles is that it is so contagious. It’s one of the most contagious diseases in existence,” says Scott Roberts, MD, a Yale Medicine infectious diseases specialist, adding that a person’s geographical risk can change quickly.

Everyone should be up to date on their measles, mumps, and rubella (MMR) vaccine, Dr. Roberts says, adding that the vaccine is the most important tool for preventing a measles infection. He spoke to us about three things everyone should know about measles and measles vaccination.

Measles starts with a cough, fever, runny nose, and conjunctivitis (pink eye), surfacing seven to 14 days after infection. Three to five days after symptoms begin, the red measles rash appears, starting on the face and spreading down the body.

In the worst cases, the disease can lead to serious complications such as deafness, pneumonia, encephalitis (inflammation of the brain), and death. Children younger than age 5, people with weakened immune systems, and pregnant women are especially at risk for a severe case.

“Measles can lead to a weakened immune system and a heightened risk of infection from other viruses and bacteria,” Dr. Roberts says. “It is also a cause of keratitis (inflammation of the cornea), which can lead to blindness.”

If you survive measles, you are also at higher risk for subacute sclerosing panencephalitis (SSPE), an incurable degenerative brain and nervous system disorder that causes symptoms such as depression, uncontrolled movements, and dementia.

Measles is highly contagious—it’s easier to catch than the flu or COVID-19. The basic reproductive number (known as the R0, pronounced “R naught”)—a metric used to describe the contagiousness of an infectious agent—is between 12 and 18 for measles, Dr. Roberts explains. That means a person with measles is likely to infect 12 to 18 people who have no immunity to the disease, he says.

The virus can be spread to others anytime from four days before to four days after the measles rash appears. It can happen after someone with the measles has coughed or sneezed, when other people breathe the contaminated air or touch an infected surface, then touch their eyes, nose, or mouth. The virus can linger on a surface or in the air for two hours.

Measles tends to spread when people who live in an area where an outbreak is occurring travel to a location that has low measles vaccination rates—places where people are vulnerable, Dr. Roberts says.

However, “communities with a high percentage of vaccinated people have herd immunity, and measles will have a hard time growing to the size of an outbreak in those places,” he says. (Herd immunity is achieved when a large majority of a population is immune to a specific disease, due to vaccination or previous infection.)

“The measles vaccine is a tremendous success story and speaks to the power of vaccination in eliminating such a contagious disease,” Dr. Roberts says.

In addition to measles, the MMR vaccine protects against mumps and rubella. Mumps is characterized by painful swelling in the salivary glands, causing puffy cheeks and a swollen jaw. Rubella, which is also called German measles, causes a mild rash and fever, but if a pregnant woman is infected, it can cause birth defects to her unborn baby.

Most people get the MMR vaccine as children. It’s given in two shots, the first typically when a child is between 12 and 15 months of age, and the second when they are 4 to 6 years old. It’s a live vaccine, meaning that it contains a small, weakened dose of the virus. This trains a healthy immune system to recognize the measles, mumps, or rubella viruses if one tries to invade the body, and attack it, preventing an infection from developing.

No vaccine is 100% effective against measles, but two MMR shots are 97% effective. (Two shots are 88% effective against mumps, and a single shot is 97% effective against rubella.) Most people who are vaccinated will never get the measles; although a small percentage have “breakthrough” cases, the symptoms are usually mild.

The MMR vaccine is also safe, according to the Centers for Disease Control and Prevention (CDC), which notes that most people have no side effects. If side effects do occur, the most common are soreness at the vaccination site, fever, and pain and stiffness in the joints. Some people may develop a mild rash in the three weeks after their vaccination, but this isn’t a concern unless they have also had a known or suspected exposure to the measles, according to the CDC.