U.S. military children in Europe should now get the measles vaccine when they are six months old — instead of the usual 12 months — because of the measles outbreak in several European countries, Army officials say.

The vaccine against measles, mumps and rubella will be available during the routine check-up with a pediatrician when infants are six months old, Regional Health Command Europe said in a release.

The MMR vaccine at six months of age would be in addition to the two doses normally given to children after they reach 12 months of age, according to the command. 

Parents are encouraged to opt for their children to get the MMR shot at six months, but while it is recommended, it isn't mandatory, officials say.

Infants who are six to 12 months old are at risk in areas where the measles virus is present "because the immunity that was passed on to them from their mothers is generally not effective beyond six months," Col. (Dr.) Rodney Coldren, chief of epidemiology and disease surveillance for Public Health Command Europe, said in the release. In the U.S., measles cases are relatively rare except for small, isolated outbreaks, so children are generally immunized at 12 months old, he said.

Officials said a second group of people is also particularly at risk for getting measles: Family members such as spouses who were born outside the U.S. and did not have the U.S. immunization schedule as children. RHCE recommends they check their immunization records to make sure they are fully vaccinated against measles. 

The outbreak of measles in Europe led the U.S. Centers for Disease Control and Prevention to issue a travel alert, as of April 17, for Belgium, Italy and Germany, and an alert starting last November for Romania.

"Getting measles vaccine is particularly important for infants 6–11 months of age (1 dose of measles vaccine) and children 1 year of age or older (2 doses of measles vaccine)," according to CDC travel alerts for European countries.

The countries hardest hit by the measles outbreak are Italy and Romania, Army officials said, with "a significant number" of cases in France, Germany, Poland, Switzerland and Ukraine. There also have been some cases in Austria, Belgium, Bulgaria, Czech Republic, Iceland, Hungary, Portugal, Spain, and Sweden.

Romania had reported 5,290 cases of measles between early 2016 and May 9 this year, according to the European Centre for Disease Protection and Control website. Germany had 504 cases between the beginning of this year and April 16. Italy had 1,920 cases between the new year and April 30.

No confirmed cases of measles have been reported among Defense Department dependents in Europe, RHCE spokesman Gino Mattorano told Army Times on Tuesday. He said a family member enrolled at the child care facility at SHAPE, Belgium, showed symptoms, and the child has been tested for measles, but the test results are still pending.

Measles is "highly contagious," with about 90 percent of people who aren't immune getting infected when exposed to the virus by another person nearby, according to CDC.

The virus can live for up to two hours in an airspace where an infected person coughed or sneezed. An infected person can spread it before knowing he or she has it, from four days before developing a rash to four days afterward, according to the CDC website.

Measles can lead to serious health complications, particularly in children under age 5, and it can be fatal.

Symptoms include fever, rash, runny nose and red eyes. These symptoms may appear one to two weeks after a person is infected, CDC says.

The RHCE recommendation for an MMR vaccine at six months old is in line with the CDC guidelines for children who are traveling.

"The MMR vaccine is a very safe and effective means to prevent this disease," Coldren said.