A new measles outbreak — along with a population improperly vaccinated in the 1960s — has many Baby Boomers wondering if they need to be revaccinated.

The recent measles outbreak in the Pacific Northwest has sent demand for the vaccine surging. Anyone who hasn’t been vaccinated is urged to get the vaccine, but do people who have already had it need another dose?

For a small subset of adults, the answer is yes.

The surge in vaccinations is happening around the Clark County, Washington, area after more than 50 people contracted the measles in an outbreak that began a few weeks ago.

The area is known for lower than average vaccination rates in children. But the outbreak may be changing some of that.

More than six times as many people were vaccinated for measles from January 13 to February 2 compared to the same period last year, a spokesperson for Washington State Department of Health told Time.

“Measles vaccination is the safest way to prevent measles from spreading, especially during an outbreak,” said Dr. Julia A. Piwoz, who heads up the pediatric infectious diseases at the Joseph M. Sanzari Children’s Hospital for Hackensack Meridian Health in New Jersey.

The rise of recent measles outbreaks is making some people who are in their 50s and 60s wonder if they were actually vaccinated for the measles virus or if they need to get their MMR vaccine refreshed.

Lori Widmer recalls getting the measles in 1963, when she was 3 years old.

“I remember being so sick I was actually glad to see the doctor, who still made house calls at that time,” recalled Widmer, whose brother contracted the illness and spread it to her and her sister.

So who needs another shot?

Measles vaccines became available in 1963. If you got the standard two doses of the measles, mumps, and rubella (MMR) vaccine after 1967, you should be protected against the measles for life.

Most people born before 1957 are thought to have been infected naturally with the virus through measles outbreaks. However there are some who are not immune.

Doctors can check a patient’s immunity levels with a blood test to detect antibodies that fight measles.

People born before 1957 who have had the lab testing that shows they are not immune and may be at high risk should have one dose of the MMR vaccine and then a second dose 28 days later.

You are at a high risk if you travel during an outbreak, are near travel hubs or destinations, or are a healthcare provider. You could be at risk if you only got one dose of the vaccine.

“Same goes for people whose blood tests show they are not immune,” Piwoz added.

The live version of the vaccine introduced in 1963 appears to have worked well, but there was another version (the “killed” version) that did not. That was also administered between 1963 and 1967.

Therefore, people who either received the killed version of the measles vaccine or don’t know what kind they received in the 1960s should be re-immunized, says the Centers for Disease Control and Prevention (CDC).

According to the CDC, those people should be receiving at least one dose of the live MMR vaccine.

Dr. Audrey K. Chun, an associate professor in the department of geriatrics and palliative medicine at the Icahn School of Medicine at Mount Sinai, said older adults are at a low risk for contracting measles.

“Most people born before 1957 were exposed to at least two major measles outbreaks, which confers immunity,” she said. Once a person has had the measles, they are immune for life. Its thse who received the vaccine between 1963 and 1967 are the exception, she noted.

Chun said that people who are concerned about contracting measles should talk to their doctor. Your doctor can then decide if another vaccination is a good idea. Receiving an extra dose of the MMR vaccine to be on the safe side is low risk, experts say.

If you were fully vaccinated, have had the disease or have a blood test that shows you are immune, then you should be protected.

Most infants are vaccinated at a year old, and then again between the ages of 4 and 6. It’s safe to give a baby the MMR vaccine at 6 months old.

“Infants who receive an MMR prior to their first birthday should still receive two doses after,” Piwoz noted.

“The vaccine cannot be safely used in some people due to problems like age, immunocompromised or allergy,” Piwoz said. “They are best protected by vaccinating those around them who can be.”

Still not sure if you need to be vaccinated? Your local health department can often offer the best advice, especially if your area is in the midst of an outbreak.

During a measles outbreak, it is important to follow recommendations from your local and state health departments, which are typically the best source of information.