The USA is experiencing a spike in measles, with 175 confirmed cases and 20 hospitalizations so far this year, according to the Centers for Disease Control and Prevention.
That's about three times the usual number of cases of measles, CDC Director Thomas Frieden said Thursday. The USA has seen nine outbreaks this year, with the largest in New York, North Carolina and Texas.
More than 98% of measles patients were unvaccinated, Frieden said.
"This isn't the failure of a vaccine; it's the failure to vaccinate," Frieden said.
The USA's overall measles vaccination rate remains high.
In fact, measles has been officially eliminated throughout the Western Hemisphere. That means that measles, unlike the flu, no longer circulates among the general population.
The USA has still had about 60 "imported" measles cases a year, however, largely diagnosed in travelers who come from abroad. Those cases mostly haven't spread beyond a couple of people, however, because nearly everyone those travelers encountered was vaccinated.
The country's safety net has become more porous in recent years, as like-minded parents who refuse vaccines have clustered in the same communities.
In August, for example, a visitor who had traveled abroad infected 15 people at a Texas megachurch. One of those infected was a 4-month-old baby, too young to have received a first measles shot.
Doctors recommend that children receive their first measles shot at age 1, followed by a second between 4 to 6 years old.
Babies traveling abroad, however, can receive a first measles shot at 6 months, Frieden said.
Many travelers are surprised to learn that some of the most popular destinations have the highest rates of measles, said William Schaffner, an infectious disease expert at Vanderbilt University School of Medicine in Nashville.
There were nearly 21,000 cases of measles in Europe in just the first six months of the year, according to the World Health Organization. Measles continues to circulate in Europe, Schaffner said, because countries there have much weaker school vaccination requirements than in the USA.
"This is an eminently controllable, eminently eliminatable childhood viral infection," said Schaffner, who notes that up to 500 Americans a year died of measles before a vaccine was introduced 50 years ago. The fact that measles continues to spread "is an ongoing tragedy."