Nine people — seven in California and two in Utah — have contracted measles after visiting Disney theme parks in California, according to state officials. Three more Californians are suspected of having the disease as well. It’s likely that they all got it from Disneyland.

All the people infected with — or suspected to have — measles had visited Disneyland or Disney California Adventure sometime between Dec. 25 and Dec. 20, according to California’s Department of Public Health. Because measles patients can be contagious for up to nine days, it’s possible that the nine people were infected by the airborne virus while visiting these parks.

Most of the people with confirmed measles were young, ranging from 8 months to 21 years old; six weren’t vaccinated. Dr. Ron Chapman, director of California’s Department of Public Health, urged people to protect themselves by getting vaccinated. “The best way to prevent measles and its spread is to get vaccinated,” he said in a statement. Because the virus is airborne and highly contagious, there’s not much else one can do to prevent it, aside from getting a vaccine.

In 2000, U.S. health officials declared measles eradicated thanks to vaccines, but it has slowly seeped back into the country due to anti-vaccine scares, as well as unvaccinated travelers re-entering the country from places where the disease is still spread. In just the first six months of 2014, there were some 288 cases of measles reported to the CDC — the highest number of cases in the U.S. since 1994, all because of “anti-vaxxers,” or people scared of vaccination.

According to the World Health Organization (WHO), measles is one of the leading causes of death among young children, even though a vaccine has been available since the 60s. It’s an airborne virus that often enters the body through the mucous membranes — causing a high fever, runny nose, cough, and white spots inside the cheeks. Then comes the measles rash, which can spread from the face and neck to the rest of the body, and lasts for several days.

Despite the fact that anti-vaccination sentiment has led to a re-emergence of measles in the U.S., at least the overall number of cases has been dropping worldwide, according to the WHO. Between 2000 and 2013, 75 percent of measles cases dropped worldwide.