Anyone who is traveling this summer should be sure they’re fully vaccinated against measles since cases of this highly infectious disease are on the rise both in the U.S. and around the world.

A passenger who was infected with measles traveled on a Turkish Airlines flight from Istanbul to Denver International Airport in May, and public health experts have traced multiple additional measles cases to the infected person.

Some people who became infected with measles were fellow passengers, while others were travelers who contracted measles at the airport. That’s because the virus that causes measles is so contagious that it can stay in the air for up to two hours after an infectious person has passed through the area. (Learn more about why measles is so dangerous, how it spreads and how to prevent it.)

The recent cases of measles prompted a new travel warning about measles from infectious disease experts at the U.S. Centers for Disease Control and Prevention (CDC).

Here are the key messages from CDC experts to help travelers stay safe from measles:

• Measles cases are on the rise around the world.
• Measles is a highly contagious respiratory illness that spreads to others through coughing and sneezing.
• All international travelers should get fully vaccinated by getting two doses of the MMR vaccine (which stands for measles mumps and rubella). (Learn why this vaccine is safe and has no connection to autism.)
• Infants should get their first dose of the MMR at between ages 6 and 11 months and a second dose when they are older. Consult with your doctor if you have questions.
• In order to be fully vaccinated for measles, children and adults need to receive two doses — at least 28 days apart — of the MMR vaccine.
• International travelers should be sure to get fully vaccinated for measles at least two weeks prior to traveling to allow for the second dose to take full effect. (Learn all about other vaccines or medications you might need before taking a trip.)
• Most people who bring measles into the U.S. are unvaccinated U.S. residents who get infected during international travel.
• Travelers should seek medical care if they develop a rash, high fever, cough, runny nose, or red, watery eyes during travel or within 3 weeks after travel.

How do I know if I’m fully protected against measles?

So, what do you need to know about measles vaccines, booster shots and breakthrough cases?

To answer your top questions, we consulted with Dr. Michelle Barron, senior medical director for infection control and prevention at UCHealth.

Barron’s key message is to get vaccinated or check your vaccine records as soon as possible. Adults should be vigilant about getting their own vaccines and should also make sure that their children are up to date as well.

If you’re not certain whether you have received the necessary doses of the MMR vaccine, check with your doctor.

A simple blood test can show whether you have immunities to measles. If you had measles as a child or you received your necessary vaccine doses, your immunity lasts for a lifetime.

Otherwise, you can get a booster shot.

“If you know that you’ve had two vaccines, then you’re set. There’s nothing more you need to do,” said Barron, who is also a professor of medicine and infectious diseases at the University of Colorado School of Medicine on the Anschutz Medical Campus.

“If you’re not sure if you’ve had two vaccines, you have the option to either get a test to see if you’re immune, or you can just get another vaccine dose,” Barron said.

What should I do if I don’t know if I was vaccinated for measles as a child? Is it safe to get a booster shot for measles?

There’s no harm in getting an extra booster dose of the MMR vaccine if you can’t find your vaccine records or if you’re unsure about your vaccine history, Barron said.

For many people, simply getting a booster dose may be the easiest choice. Getting sick with measles can be very dangerous, especially for children. (Learn more about what it’s like to have measles and which treatments do and don’t work.)

Here are basic guidelines by age for who may need a measles booster shot:

• People born before 1957 do not need a booster. They likely got measles as a child.
• People born between 1957 and 1967 should check with their doctor and may want to get their blood tested. They might have received a less effective dose of the measles shot as a child.
• People born between 1967 and 1989 likely got one dose, and some may need a booster. Check with your doctor.
• People born after 1989 who have received two doses of the vaccine should be fully vaccinated and well protected.
• If you were never vaccinated as a child, call your doctor and get vaccinated now.
• If you don’t know your vaccine history, talk to your doctor and develop a plan to protect yourself from measles.

What about breakthrough cases in vaccinated people? Should I worry about getting measles even if I’m fully vaccinated?

A small percentage of people who have gotten confirmed cases of measles recently have been fully vaccinated and still contracted the illness. That’s known as a “breakthrough case.”

Barron said the chances of breakthrough cases are very low — less than 3%. Here’s information from Barron and CDC experts about breakthrough cases.

“The vaccine is 97% effective for people who have gotten two doses and 93% effective after one dose,” Barron said.

“Breakthrough cases are uncommon, but if there’s a high level of measles circulating, a small percentage of people could get a breakthrough infection,” she said.

Barron advises fully vaccinated people not to worry about breakthrough measles infections because they are so rare.

Her advice about staying safe from measles is simple for people who are traveling and for all others: Be sure you and your children are fully vaccinated.

Barron said it’s critical for all of us to protect ourselves, our families and our communities from this dangerous disease.

Measles once infected more than half a million people every year in the U.S. Once people in the U.S. got measles vaccines, the case numbers plummeted nearly to zero in 2000. That’s when health officials declared that measles had been eradicated in the U.S.

The disease recently has been making a dangerous comeback.

“Because of misinformation and outright lies about the MMR vaccines, people are hesitant (about getting the MMR vaccine) and we’re now facing these consequences,” Barron said.

“The MMR is highly effective and incredibly safe. There’s no link to autism. That was debunked a long time ago,” Barron said.

“The vaccines don’t cause you any ill effects — other than maybe a sore arm. The flip side is that measles is very dangerous. It can cause pneumonia and swelling in the brain, and it can result in death. A lot of the people who have been hospitalized due to measles have been children. This is not something to be taken lightly,” Barron said.

“As an adult, if you end up getting measles, you may not need to be hospitalized, but you may spread measles to your kids, or you may spread it to other people who are vulnerable. And this is not OK,” Barron said.

Aside from being fully vaccinated, how can travelers stay safe from measles?

“The main thing to remember is that we’re not only seeing increases in measles cases in the U.S. We’re also seeing them in Canada and Mexico, and Europe is also having outbreaks, so your risk of getting measles if you’re traveling is still quite high,” Barron said.

Take time to check with your doctor before traveling so you can make sure you have all the necessary vaccines or medications you need. And once you are headed to the airport, you can take additional steps.

“You can wear a mask,” Barron said. “The fact that multiple people on the Turkish airlines flight and people at DIA (Denver International Airport) all got infected tells you how much of the virus was spreading.”

Barron said people have taken their safety for granted when it comes to vaccine-preventable diseases.

When doctors and infectious disease specialists are doing their jobs — and people are doing their part by getting their recommended vaccines — preventable diseases, like measles, don’t pose a risk.

“People take for granted the impact of infection prevention because nothing happens. It’s like wearing your seatbelt. If you’re in an accident, you will be OK. That is the outcome you want,” Barron said.

“Now, all of a sudden, we are starting to have measles cases again, and that makes me sad because we can prevent them,” Barron said.

She urges people to “put on their seatbelts” when it comes to preventable diseases. Get vaccinated and stay safe.