Measles has all but disappeared from the United States for the past decade but risks a comeback due to a growing number of parents who refuse to vaccinate children, experts said Thursday.
Fifty years after a vaccine against the highly contagious viral infection was approved, the US strategy of blanket immunization has proven a victory for public health, said the findings in the Journal of the American Medical Association.
"The United States is the most populous country to have documented elimination of endemic measles," said the study, which is based on the findings of a Centers for Disease Control and Prevention expert panel.
Measles was held to a very low incidence of less than one US case per million from 2001 to 2011, said the study.
Two related viruses are also way down in the United States: rubella, which has been below one case per 10 million births since 2004 and congenital rubella syndrome (CRS), which is down to one case per five million births, it added.
But while measles has vanished from the Western hemisphere, it remains common elsewhere, including in parts of Africa and Asia, and kills as many as 18 children per hour around the globe.
Malnourished children are particularly at risk for complications of measles, which typically causes fever, rash, eye infection and white spots in the mouth.
More serious complications include blindness, pneumonia, brain damage and severe dehydration.
It remains a leading cause of death among children worldwide, and killed 158,000 people in 2011, according to the World Health Organization.
Over the 10 years studied, there were 911 total cases of measles reported in the United States, most in people who were unvaccinated or were unsure of their vaccination status.
The CDC said there were typically about 60 cases per year, but 2013 "saw a spike in American communities—some 175 cases and counting—virtually all linked to people who brought the infection home after foreign travel."
Measles importations were associated with travel from 57 countries. A handful of countries—China, Japan, India, Italy, the Philippines and Britain—were each linked to 20 or more cases.
"A measles outbreak anywhere is a risk everywhere," said CDC Director Tom Frieden.
"The steady arrival of measles in the United States is a constant reminder that deadly diseases are testing our health security every day.
Certifications from other countries in the Americas mean "the entire Western hemisphere will be certified free of indigenous transmission," said an editorial by Mark Grabowsky, of the Office of the Secretary General's Special Envoy for Financing the Health Millennium Development Goals and for Malaria.
He called the efforts a "triumph of public health" but warned that risks remain.
"The greatest threat to the US vaccination program may now come from parents' hesitancy to vaccinate their children," he wrote.
"Although this so-called vaccine hesitancy has not become as widespread in the United States as it appears to have become in Europe, it is increasing."