Here’s how to avoid these dangerous outbreaks during your summer travels.

The FIFA World Cup starts today with millions of expected visitors, including tens of thousands of Americans.

But American soccer fans are getting a warning from the public health officials: Make sure you’ve had your measles vaccination.

Last year, Europe had a four-fold increase in measles cases compared to the year prior. The Centers for Disease Control and Prevention (CDC) wants to make sure Americans are protected and don’t bring back measles to this country.

“We actually recommend that all travelers are up to date with all the routine vaccinations,” Dr. Gary Brunette, chief of the Travelers’ Health branch for the CDC, told Healthline.

The FIFA World Cup Russia runs June 14 to July 15, and more than 2.4 million tickets have already been sold.

Aside from the World Cup, millions of Americans will travel abroad to Europe this summer.

So what’s the risk of measles arriving here from an infected vacationer?

“The risks are probably pretty darn low,” said Dr. William Schaffner, an infectious disease specialist at the Vanderbilt University School of Medicine. He added that increases of measles cases in Europe have occurred before and resulted with very few importations of the disease into the United States via infected travelers.

The reason for these periodic outbreaks, according to Schaffner, is the lack of comprehensive and routine measles vaccinations for children in many European countries.

Though that might be changing — with France and Italy recently passing legislation that would make these vaccinations more routine — there are still susceptible children and adults in those areas, he said.

While the U.S. practices systematic measles, mumps, and rubella (MMR) vaccination, there have been instances of parents withholding vaccinations for their children for fear of side effects.

It’s these unvaccinated children and adults that are at risk of contracting the virus when traveling to areas with active infections, according to Schaffner.

“I wouldn’t want any child to go through a case of measles,” he said. “It can be a very unpleasant risk to your health, seriously.”

In addition to fever, chills, cough, stuffy nose, conjunctivitis, and rash, complications can include middle ear infections and pneumonia. Schaffner said that one in a thousand of those who contract the measles can suffer from a very serious inflammation of the brain called measles encephalitis.

“The older you are… the more likely you are to be really sick and develop the complication of pneumonia,” he said. “Before we had measles vaccinations in the mid-1960s, we had 400 children die of measles and its complications in the U.S. each year.”

Schaffner advises that any travelers heading to the World Cup, and travelers to Europe in general, receive at least one of the two MMR vaccines recommended before the trip.

“That’ll provide very substantial protection to the vast majority of people and when you get back, get that second dose,” he said.

A single dose of the MMR vaccine provides 93 percent protection against measles and two doses provides 97 percent protection.

MMR vaccine side effects are typically minor, according to Schaffner, including the occasional sore arm, and a couple of degrees of fever in a small percentage of the population.

He does caution that the vaccination is made of weakened live attenuated viruses and isn’t to be given to anyone with a weakened or compromised immune system.

Beyond Europe, travelers planning summer trips may confront news of scarier-sounding outbreaks, including the deadly Ebola virus in the Congo and Nipah virus in South India.

Brunette said while world and local health officials are actively involved in containing the outbreaks, there’s currently no real concern of the viruses spreading.

“We watch these situations, we watch them very closely,” he said. “It’s typically a localized outbreak, and though it’s a concerning outbreak, we don’t think there is significant risk of importation into the United States.”

He said the locations of outbreaks are very remote and difficult to reach — which means the viruses are more likely to stay contained. If someone did travel into those areas, they would be advised to avoid contact with sick or dead people, or bodily fluids from these people, said Brunette.

There are other diseases endemic to countries that pose ongoing public health risks, including the Zika virus in Central and South America, the Caribbean, and other places, he said.

Pregnant women are most at risk and shouldn’t travel to areas with risk of infection.

“We are not trying to make people scared about traveling,” he said, adding that travelers can inform themselves on these diseases on the CDC Travelers’ Health website. “We’re encouraging healthy traveling.”

In addition to travel safety, Brunette said that the United States has a robust public health system in place in case of an outbreak.

The CDC works closely with customs and border protection officers for regular training. “They are trained to recognize illness in ports of entry,” he said.

If someone is sick, they could be held back for further evaluation. The CDC also has quarantine stations at 18 airports in the country.

In the event that a sick person developed symptoms after arriving in the United States, there’s also a reporting system in place starting at the doctor’s office. Physicians are trained to always ask patients who are sick if they’ve recently traveled.

When something unusual is noted, the doctor notifies that state’s health department. If a larger response is needed, the CDC is notified.

In a hypothetical Ebola case, Brunette said “within minutes to hours, CDC would be informed. CDC would be reacting, responding, along with the state.”