(AP) -- The United States seems to be on track to have more measles cases than any year in more than a decade, with virtually all cases linked to other countries, including Europe where there's a big outbreak.
Already there have been 89 cases reported so far. The U.S. normally sees only about 50 cases of measles in a year thanks to vaccinations.
Health officials are reluctant to make predictions, but acknowledge the pace of reports is unusually hot.
"It's hard to say, but we're certainly getting a lot," said Dr. Greg Wallace, who leads the measles, mumps, rubella and polio team at the U.S. Centers for Disease Control and Prevention.
Europe, especially France, has been hit hard by measles, with more than 6,500 cases reported in 33 nations. International health officials are blaming it on the failure to vaccinate all children.
Just about all U.S. outbreaks were sparked by people bringing it here from other countries. This week, international health officials posted an alert urging travelers everywhere to get the recommended two doses of vaccine before flying overseas.
"The risk of getting infection is very high," said Dr. Cuauhtemoc Ruiz Matus, an immunization expert with the Pan American Health Organization.
In the U.S., the worst year for measles in the last decade was 2008, when 140 cases were reported. There have been no measles deaths this year, but health officials warn the disease can be dangerous.
Measles is highly contagious and up to 90 percent of people exposed to an infected person get sick, experts say. The virus spreads easily through the air, and in closed rooms, infected droplets can linger for up to two hours after the sick person leaves.
"Measles is really the most contagious of the vaccine-preventable diseases. It has a knack for finding those who have not been vaccinated," Wallace said.
The disease's most common symptoms include fever, runny nose, cough, eye inflammation and rash all over the body. It takes about two weeks for the rash to appear from the time of first infection, and people are contagious from four days before a rash to four days after.
A small fraction of people get much sicker, developing pneumonia or even encephalitis. For every 1,000 children who get measles in developed nations, one or two will die.
Since 2003, there have been no measles-related deaths reported in the United States, where children have been getting vaccinated against the virus for almost 50 years. Before the vaccine, nearly all children got measles by their 15th birthday and epidemics cycled through the nation every two to three years - generally peaking in the late winter or spring.
In those days, about 450 to 500 Americans died from measles each year, on average. Vaccination campaigns reduced the toll dramatically, and today, roughly 90 percent of U.S. kids are protected from measles, according to studies of teenagers.
Two doses of a measles-mumps-rubella vaccine are routinely recommended for all children, including a first dose given around a child's first birthday and a second dose around the time of preschool. These vaccinations are believed to last for a lifetime.
Children as young as six months old can get a first dose if they're going to a country where they are at high risk of exposure, health officials say.
"Unfortunately, that's not always done. Parents often don't report to their physician that they are taking their child on an international trip," said Dr. Harry Keyserling, a pediatric infectious diseases specialist at the Emory University School of Medicine.
One dose is considered 95 percent effective, two doses even better. But health officials acknowledge it's not perfect and a few people who are fully vaccinated will still get sick.
Of the 89 cases reported through the end of last week, 79 were people who were unvaccinated or who had no documentation of it, Wallace said.
Outbreaks so far this year have included:
-In Florida, five cases linked to an international helicopter trade show held in Orlando last month, and another three cases in an outbreak in the Gainesville area traced to a traveler who had been to India.
-Nine cases in Utah, reported last month. They were linked to someone who apparently was infected in Poland.
-Twenty-one cases in Minnesota, first reported in February. The illnesses were traced to a Minneapolis-areas child who developed symptoms after returning from a trip to Kenya.
-Six cases in Pennsylvania, first reported in January, origin unknown.
Explore further: Measles scare keeping students in Canada