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A major outbreak of measles in Europe raises questions about the disease’s ability to spread locally, or even internationally.

Last week the on the rise of measles in countries throughout the European Union, including France, Germany, Poland, and Ukraine.

However, the largest outbreaks were seen in Italy and Romania — the latter reporting in early July there had been more than 3,400 cases of the disease as well as since June 2016.

Overall in Europe, 35 people have died from measles during the past 13 months.

These incidents have members of the international health community wondering how such a thing could happen with a disease largely .

Read more: Measles vaccine also protects against other infectious diseases »

How can it spread?

Since the introduction of a vaccine in 1963, cases of measles have dropped to historically low levels.

The U.S. Centers for Disease Control and Prevention (CDC) announced that in the year 2000, the disease was eliminated from the country — meaning that over a year passed without continuous transmission of the disease.

Furthermore, the World Health Organization (WHO) has committed to “” the disease from the globe by 2020.

However, without proper vaccination practices, that may not happen.

According to the CDC, in the United States have steadily risen from a low of 37 people in 2004 to a high of 667 in 2014.

The disease targets young children who have never been exposed to it.

As Healthline reported last year, research published in JAMA stated, “greater emphasis needs to be placed on the association between vaccine refusal and the increase in [measles].”

In fact, the rise of contagious diseases largely considered neutralized by the CDC and WHO, such as measles and pertussis (whooping cough), is largely attributed to the anti-vaccination movement.

In 2015, California reported 59 cases of measles, with 42 of them linked to groups of unvaccinated children at Disneyland.

Dr. Stephen Lauer, vice chair of pediatrics at the University of Kansas Health System, tells Healthline, “The decrease in vaccination rates due in large part to the misinformation spread by the ‘anti-vax’ movement, is responsible for the spread of vaccine-preventable diseases.”

Read more: Measles vaccine doesn’t lead to autism, even in high-risk families »

Traveling across the oceans

Measles is highly contagious and, according to Lauer, without addressing proper vaccination procedures, there is a possibility for the current outbreak in Europe to make its way to the United States.

“The basic reason for the European outbreak is a decline in protective vaccination rates. If we follow the same path in the U.S., we can expect the same result,” he said.

Because of U.S. efforts to protect against the disease domestically, most cases of measles are brought into the country by .

With the speed of global travel, unvaccinated, infected individuals can easily travel from country to country spreading disease.

Airplanes facilitate the process.

“A susceptible person could be exposed to a case of measles,” said Lauer, “travel for up to 24 hours, get off the plane, clear security, and not become ill for three to 10 days.”

To protect against highly contagious diseases, humans depend on a phenomenon called “herd immunity.”

The greater the number of vaccinated individuals in a group, the chance a disease is able to spread within that group decreases.

“The infected unvaccinated person either gets better or dies, and if he doesn't come in contact with another unvaccinated person the virus can't spread,” explained Lauer.

In the case of a particularly communicable disease like measles, the recommended vaccination rate for a population is 95 percent to achieve herd immunity.

The recent outbreak in Europe has largely cropped up in areas where immunization levels have dipped beneath this threshold.

Read more: Some adults need to be revaccinated against measles »

An easy solution

The answer to the problem remains the same as it’s been for the past 50 years: Vaccination.

According to WHO, measles vaccinations have saved over 17 million lives since the year 2000. In order to completely eradicate the disease, countries across the globe will have to focus their efforts on vaccination.

When it comes to measles, Lauer is blunt: “Prevention is always safer, more effective, and less expensive than treating infection.”

“As vaccination rates decline and infection rates rise,” he added, “we can expect to see deaths and serious morbidity from measles in the U.S. despite our outstanding care for those who become ill.”