In the recent Boston outbreak, many of the infections occurred in people who were vaccinated during the mid-1960s.
"Mostly we saw cases [in people] that were U.S.-born, people in their 30s to 50s," said Anita Barry, Boston's director of communicable disease control.
"[T]hey were people that were born too late to be naturally exposed to the measles disease, yet they were born too early for a reliable vaccine to be around.
"For a variety of reasons they didn't have [immunity], but most of them thought that they were fully protected," she added.
"They said, I've had all my childhood vaccines. I should be fine."
There were no fatalities in the Boston outbreak, but measles is by no means harmless.
The disease is highly contagious and causes fever, rash, and flulike symptoms. The telltale rash can also be accompanied by diarrhea and more serious conditions including pneumonia and brain inflammation.
The World Health Organization estimates that some 450,000 people worldwide, mostly children, die from measles each year.
"Live" or "Killed"?
Barry says that U.S. citizens born after 1957 are considered at risk unless they have documentation that they were vaccinated with a "live" measles vaccine rather than a "killed" measles vaccine.
Live vaccines use a living but weakened form of the measles virus to immunize patients against the disease, while killed vaccines use dead viruses.
Adults with unknown vaccinations, or those vaccinated with killed measles vaccine, may want to consider receiving another dose of the vaccine, Barry says.
Measles vaccinations are effective up to 72 hours after a person has been exposed to the disease, so Boston health officials took action to track the outbreak's spread and administer preventive vaccines to Hancock Tower employees and others believed to be at high risk.
"One case in this outbreak was a fellow who worked in a restaurant, and some of his coworkers had no evidence of immunity to measles either through vaccination or being born [in the U.S.] prior to 1957," Barry explained.
"But their exposure was such that it had been less than 72 hours, so a group of nurses went down to the restaurant and vaccinated them."
Another measles outbreakthe largest in the U.S. in ten yearsoccurred last year, when a 17-year-old Indiana girl contracted the disease on a trip to Romania.
After her return, the girl, who was not vaccinated for the disease, attended a church function with many others who were also unvaccinated.
Sixteen parishioners were infected, and they in turn infected others with whom they had contact.
Thirty-four people eventually got the measles, according to the U.S. Centers for Disease Control and Prevention.
The Indiana outbreak struck another group of Americans at special risk from the measlesthose who refuse to be vaccinated.
Some people shun vaccination because they believe that vaccines preserved with thimerosal, a mercury compound, can pose health risks such as autism.
The Washington, D.C.-based Institute of Medicine reports that no link has been established between thimerosal and autism and that the ingredient is being phased out of most childhood vaccines.
"There are some people who fear immunizations because of beliefs, which have no basis in scientific data, that immunizations could be harmful," said Charlene Graves, medical director for Indiana's state immunization program.
"If these families don't immunize their children, other people can be put at risk of disease. The reason [the Indiana outbreak] wasn't even more widespread is that the great bulk of people are adequately immunized against measles."
Most of Indiana's measles victims were homeschooled children who would have been exempt from the state's public school system vaccination requirements.
"To me one of the main messages is that if this 17-year-old child had been vaccinated, or if whomever sent her on the trip had vaccination requirements for international travel, the whole outbreak could have been prevented," Graves said.
How Outbreaks Were Contained
In both the Boston and Indiana outbreaks, unvaccinated people who may have been exposed to the measles were subjected to isolation and quarantine to remove potentially infected people from the general population.
"People are free to make their own choices," Boston's Barry said.
"We don't force vaccine on people, but we do enforce quarantine and isolation laws. If you're exposed, and you don't want a vaccine, you need to stay at home where you won't be giving other people this disease."
"Our experience has been that people comply with that."
Schuchat, of the National Center for Immunization and Respiratory Diseases, says that the best way to battle measles is to extend the fight around the world, particularly to Africa and Asia.
(See National Geographic magazine's "Tracking the Next Killer Flu.")
To that end an international campaign called the Measles Initiative has administered over 200 million vaccinations since 2001.
The initiative combines the efforts of the U.S. Centers for Disease Control, the UN, and the American Red Cross to make vaccinations more accessible in the developing world.
"In the United States, we're very lucky that we have high immunization coverage," Schuchat said.
"Some other countries don't have strong policies at all. But we're in much better shape today than we were five or ten years ago in terms of [a global fight against measles.]"
More on Resurging Diseases
Polio's Rapid Comeback Poses Epidemic Risk, Scientists Say (September 12, 2006)
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