A measles outbreak at Disneyland in southern California highlights the importance of vaccinating against preventable diseases.

Disneyland is supposed to be a place for magic, not measles.

Jose Fuentes spent the latter part of 2014 discovering it really is just “a small world after all”: He spent Halloween at Disneyland in Anaheim, California and Christmas at Disneyland Paris in France with his fiancée and their 2-year-old daughter, Naia.

Like any typical toddler, Naia loved meeting Mickey Mouse. And Naia’s parents loved that their only child didn’t get sick during their travels.

“Naia is up-to-date on her shots. We make sure she’s good on that,” Fuentes told Healthline. “I do believe vaccines will do some good, especially since she is brand new to this world and there are a lot of things she hasn’t been exposed to.”

However, other visitors to popular Disney attractions have become infected with measles, one of the most contagious diseases humanity has ever faced. The disease can infect up to 90 percent of exposed people who are not immune, and it is one of the leading causes of death among children.

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According to an AP story on January 16, investigators have confirmed at least 39 cases originated from Disneyland or Disney’s California Adventure Park. Most of those infected visited the park between December 15 and 20, a popular time of the year for “the happiest place on earth.” The outbreak has reportedly spread to Utah, Colorado, and Washington.

The outbreak supposedly began when an unvaccinated 20-year-old California woman visited the park and then took flights through two major airports to spend time with family in Seattle, the Los Angeles Times reported.

Officials say the majority of those infected weren’t immunized for measles. They were either too young or chose not to receive the immunizations for personal beliefs.

“The best way to prevent measles and its spread is to get vaccinated,” Dr. Ron Chapman, director of the California Department of Public Health, said in a statement

Due to high vaccination rates, measles was declared eliminated from the U.S. population in 2000. Still, the U.S. Centers for Disease Control and Prevention reported a record number of cases in 2014: 644 cases in 27 states.

Measles spreads through the air and through direct contact. Recent outbreaks have occurred in clusters of unvaccinated people, including a Texas megachurch whose no-vaccination message was linked to a measles outbreak in 2013.

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Outbreaks occur for multiple reasons, but the ease of international travel and the rising rate of unvaccinated individuals have contributed to most outbreaks.

In California, around 90 percent of the children in childcare facilities received all of the required vaccinations. Approximately 2,734 children, around 1 percent, were not vaccinated because of permanent medical exemptions. Personal belief exemptions accounted for almost 3 percent, or 12,981 children.

In response to the resurgence of preventable diseases like measles and whooping cough, many states are passing legislation to cut down on personal belief exemptions allowed for children entering public education.

The World Health Organization calls the measles vaccine “one of the best buys in public health” because the vaccination prevents about 1.2 million deaths a year and is relatively inexpensive.

Not everyone can be vaccinated. Young children or people with compromised immune systems, such as those undergoing cancer treatments or people with HIV, aren’t healthy enough to be vaccinated against the virus. But when those who are eligible for vaccination do so, they create a safer environment for the entire community. When large groups of a population are vaccinated against an infectious disease, the majority of the people in that community are protected from the disease (even those who are not vaccinated) because the chance for an outbreak is low.

However, an increasing number of parents don’t have their children vaccinated because they think it causes autism. Fuentes doesn’t have such concerns for his daughter.

“There’s that whole thing with Jenny McCarthy saying that she believes that her son’s autism was caused by the vaccines, but what kind of factual information does she have to prove that point?” Fuentes said.

The information sparked a frenzy of frantic headlines in 1998 when a now-debunked study suggested the measles, mumps, and rubella (MMR) vaccine caused autism. And although the study was retracted due to faulty research and conflicts of interest, the study — vocalized by McCarthy and other mothers — has contributed to the decline of infant vaccination rates.

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International travelers should receive needed vaccinations to protect themselves and to protect others as well. This includes measles, tuberculosis, and the seasonal flu vaccine.

The CDC recommends that anyone over the age of 6 months, including pregnant mothers, get a flu shot.

Despite his belief in vaccinating his daughter, Fuentes admits he’s behind on his yearly flu shot.

“I have gotten the flu shot once, and now I’m thinking it’s time I go get it,” he said. “I have been sick on and off for the last two months, and I think it’s because I haven’t gotten vaccinated.”

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