BERLIN » An 18-month-old boy has died of measles in Berlin, the first known death in an outbreak of the disease that has seen more than 570 cases in the German capital since October.

An autopsy on the child, who died on Feb. 18 and wasn’t immunized against measles, showed he had an unspecified medical condition, but it wouldn’t have led to his death without the measles infection, the Charite hospital said Tuesday.

The German outbreak coincides with smaller ones in the United States, where 154 measles cases have been reported this year, three-quarters of them tied to an outbreak that started in Disneyland in December.

Authorities believe the Berlin measles infections began with a child from Bosnia whose family was seeking asylum. The highly contagious illness then spread, partly because many older adults in Germany were never immunized and many younger adults received only one vaccine instead of two, as is now recommended for full protection. About half of those infected were adults, officials said.

Although it’s rare for measles to be fatal in developed countries, the disease remains one of the leading causes of death among young children globally, despite the availability of a safe and effective vaccine.

The virus kills up to 10 percent of children infected in developing countries that have high levels of malnutrition and poor health care. Approximately 145,700 people died from measles in 2013, mostly children under the age of 5, according to the World Health Organization. Most measles deaths are caused by complications associated with the disease.

"There’s a misconception that measles does not kill in developed countries, but it unfortunately still happens," said Dr. David Elliman, an immunization expert at Britain’s Royal College of Paediatrics and Child Health, citing similar deaths in the U.K. in recent years, mostly among people with other health problems, like asthma.

Elliman said measles kills about 1 in every 1,000 people in developed countries and that the death in Germany wasn’t entirely unexpected given the size of the outbreak. Berlin last had a major measles outbreak, with 493 cases, in 2013.

Health officials say more than 95 percent of a population needs to be vaccinated to prevent outbreaks. Vaccination rates across Europe fell after a now-discredited study that suggested a link between autism and the vaccine for measles, mumps and rubella.

Dr. Adam Finn, a professor of pediatrics at Britain’s University of Bristol, said the relatively large number of adults infected in the current outbreak in Berlin exposes problems in previous immunization programs. A 2013 study found vaccination rates among young adults 18-29 of around 80 percent, while less than 4 percent of people ages 60-64 were vaccinated.

The measles vaccine was only developed about 50 years ago, which would explain why many older adults didn’t get the shots, though many are thought to be protected because they’ve had measles. Germany has had a nationwide recommendation of a two-shot regimen only since 1991, so many younger adults did not receive the second dose.

By contrast, vaccination rates are high for young children. The Robert Koch Institute, Germany’s equivalent of the Centers for Disease Control, says that 97 percent of children had received one measles shot and 92 percent the full two doses by about age 7 in 2012, the last year for which figures were available. A decade earlier, only around a third of children had received a second shot.

In the U.S., immunization is recommended in children at 12 to 15 months of age, followed by a second dose for full protection, usually before the child starts school at 4 to 6 years old. The two-dose protocol was adopted in 1989.

Germany’s health minister, Hermann Groehe, called Monday for increased efforts to ensure children are vaccinated and said that if that fails, authorities might consider making immunizations mandatory, though he said that isn’t currently on the agenda.

Groehe has criticized the "irrational scaremongering" of some vaccination opponents, though local officials say many of those infected in Berlin appear to simply have been unaware of the risk they faced from under-vaccination rather than opposition to immunization.

Other experts were unconvinced a mandatory vaccination policy would work.

"That could end up backfiring on you, if people are absolutely opposed to getting the vaccine," said Finn, who said the idea of compelling parents to vaccinate their children was controversial.

"Everyone is agreed that getting the vaccine is the best way to stop outbreaks, but how we get people to do that is another story," he said. "I’m not sure making vaccination mandatory is the solution."

German officials say at least two cases in Berlin have been linked to the U.S. — one person who developed symptoms there before traveling to Germany and another who developed the infection after returning.

A Berlin high school was closed Monday because a student had measles, but reopened Tuesday. Officials checked students’ and teachers’ vaccination records and a local health official, Sibyll Klotz, said five students who couldn’t show they were properly vaccinated were sent home, the DPA news agency reported.

Associated Press writer David Rising in Berlin and AP Medical Writer Maria Cheng in London contributed to this report.