Between January 1 and October 31 of this year, the Centers for Disease Control and Prevention (CDC) confirmed 603 cases of measles in 22 states—the highest number since 1994—marking a striking resurgence of a disease that was declared eliminated in the United States in 2000.
The cause is twofold, according to a recent report in the New England Journal of Medicine: importation of the virus into the United States by travelers from countries where measles is still common, and a growing number of parents in this country who hesitate to vaccinate their children.
Measles is endemic or epidemic in some countries in Europe, Asia, and Africa. This year so far at least 48 cases of measles have been brought into the United States by travelers from more than 30 countries, especially the Philippines, where a large measles outbreak persists, the CDC reports.
Once introduced from abroad, measles can spread among the unvaccinated. The hazard is compounded by a gradually increasing number of children whose parents choose not to have them vaccinated for nonmedical reasons—that is, philosophical objections arising from the belief that vaccinating is riskier than not vaccinating. The more children who remain unvaccinated, the less protection offered by herd immunity. The vaccination rate needed to achieve herd immunity and interrupt measles transmission is around 92% to 94%--higher than for most other vaccine-preventable diseases.
Measles is highly contagious. An infected person can spread it to 12 to 18 susceptible contacts. The disease often leads to complications, including otitis media, diarrhea and dehydration, pneumonia, and encephalitis. An estimated 0.2% to 0.3% of infected persons in the United States die of measles; the death rate in developing countries is as high as 2% to 15%.
The World Health Organization (WHO) reports that around 145,700 children worldwide died from measles in 2013, 23,700 more than in 2012. Progress toward eliminating the disease globally has stalled as lack of money, weak healthcare systems, and low awareness of the importance of vaccination hamper immunization efforts, WHO says.
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