Before you pack up for that summer vacation or send the kids off to camp, you may want to check if everyone’s immunizations are up to date.

This year, the United States is dealing with the worst measles outbreak since 1994, with the Centers for Disease Control and Prevention reporting more than 940 cases confirmed in 26 states. Those include seven cases in Allegheny County, Pa., as of May 15, and 14 cases in Ocean County, N.J., as of May 22.

Many of the U.S. outbreaks, including the one in the Pittsburgh area, can trace their origins back to other countries including Israel and the Philippines, because unvaccinated individuals who were traveling internationally brought in the highly contagious disease. Others, such as one in New York, are being blamed on vaccine refusal in certain communities.

The measles vaccine should be considered a travel vaccine much like those for typhoid and yellow fever, said Stephen Gluckman, professor of medicine at Penn Medicine and the medical director of Penn Global Medicine. If individuals are going to an area where there is risk, they should be vaccinated, he said.

The measles vaccine normally is given as part of the MMR (measles-mumps-rubella) inoculation; mumps has also been a problem this year, though medical officials say that can be because the mumps portion of the vaccine appears to lose strength over time.

Most adults born before the 1960s were exposed to the virus as children and likely are not vulnerable to reinfection. However, adults inoculated in the 1960s should talk to their doctors, as some of the vaccine used in that period appears not to be protective. A blood test can show if you have immunity, or you can just get another MMR vaccination.

Here’s what you need to know about summer travel and risk of outbreaks:

Planes

There is a misconception about air travel and getting sick, Gluckman said.

With the efficient air exchange system, which includes high efficiency particulate air (HEPA) filters, some of the safest air we breathe is on planes. If you are sitting next to someone who is contagious you might get sick, but for those seated four to six rows away, the risk is almost nonexistent, Gluckman said.

Cruises

Even if you’re up to date on immunizations, if a fellow traveler who hasn’t been vaccinated comes down with highly contagious measles, you may get caught up in a quarantine similar to the one on the Church of Scientology cruise ship Freewinds. The ship was quarantined at the end of April when it arrived in the Caribbean nation of St. Lucia with a female crew member who was found to have measles. It took nearly two weeks before the more than 300 passengers aboard could leave the ship.

To try to head off any problems, Carnival Cruise Lines requires its crews to be vaccinated for measles, mumps and rubella, said spokesperson Vance Gulliksen in an email.

The cruise line works with the CDC on plans to minimize the spread of all contagious diseases, which included strict isolation of any suspected cases of measles and reporting such incidents to local and national public health authorities, he stated.

Theme parks and other summer events

An outbreak at a large event or even a theme park could also derail your plans.

In 2015, there were 147 reported cases of measles linked to Disneyland in California.

Closer to home, the Little League World Series, held every year in Williamsport, Pa., was the site of a measles outbreak more than a decade ago. A member of the 2007 Japanese team set off an outbreak that sickened at least seven individuals in three states. More than 265,000 participants and spectators were at the event that year.

In an emailed statement, Little League International officials said they work directly with the Pennsylvania Department of Health and local medical officials on any health concerns.

Currently, the state Health Department has no plans to reach out to U.S. or foreign teams as a precaution, said spokesperson Nate Wardel. But that could change if it continues to see a rise in cases, he said.

Those precautions could be similar to what health officials did during a mumps outbreak earlier this year that involved Pennsylvania State University during its big cancer fund-raiser, known as Thon. The department sent a warning to families of the children who were planning to visit letting them know about the risk, he said.

Camp

The American Camp Association is taking a proactive approach to this year’s increase in measles.

As 10.3 million children start to descend on the more than 14,000 overnight and day camps in the United States, the group issued a measles update on its website.

“Anytime there is an outbreak we make sure to update the members,” said Kelley Freridge, spokesperson for the group.

The group also outlines tips for camps on how to put in place procedures to screen for illness, injury, and communicable diseases including measles as campers arrive, Freridge said.

The American Association of Camp Nursing also recommends that every child be fully immunized for vaccine-preventable diseases.

“With all the measles outbreaks, we don’t know what it will look like over the next few months,” said Tracy Gaslin, executive director.

This year, there are camps that are drawing a hard line in the sand by allowing only kids who can show proof of vaccination to attend. An outbreak could mean a two- to three-week quarantine in some states. If they run one-week camps they would have to eliminate sessions and it could affect their bottom line, she said.

“The key to all of this is prevention,” Gaslin said.