So far this year, 118 cases of measles have been reported to the Centers for Disease Control and Prevention (CDC) — the highest number for the January-to-May period since 1996 and double the median number of yearly cases reported from 2001 to 2008.
Infections were reported in 23 states and New York City in patients ranging in age from 3 months to 68 years. Forty percent of those affected required hospitalization; nine developed pneumonia, but none died.
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Because of routine vaccination, measles — a highly contagious viral disease — was eliminated from the U.S. in the 1990s, but cases are still imported into the country each year from other regions where the disease is still endemic.
Of the 118 cases reported in the first 19 weeks of 2011, 89% were associated with importation from other countries, meaning that American travelers contracted measles abroad and spread it when they got home, or foreign travelers brought measles to the U.S.
The spike in cases this year is due in part to recent increases in measles in other parts of the world, namely South East Asia and Europe — this year 33 European countries have reported increases in measles, stemming mostly from France, where the outbreak reached 10,000 cases (including six deaths) in the first four months of the year.
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Notably, 89% of the 118 cases in the U.S. involved unvaccinated patients; of the 47 who were hospitalized, all but one had not been vaccinated. Recently, there have been declines in routine childhood vaccination rates in some areas of the U.S. due to fears about vaccine safety and the false belief that vaccines trigger with autism in children. The CDC reports:
Among the 45 U.S. residents aged 12 months−19 years who acquired measles, 39 (87%) were unvaccinated, including 24 whose parents claimed a religious or personal exemption and eight who missed opportunities for vaccination. Among the 42 U.S. residents aged ≥20 years who acquired measles, 35 (83%) were unvaccinated, including six who declined vaccination because of philosophical objections to vaccination. Of the 33 U.S. residents who were vaccine-eligible and had traveled abroad, 30 were unvaccinated and one had received only 1 of the 2 recommended doses.
When people refuse or fail to complete vaccination, it puts others in the community at risk, especially babies under age 1 who are too young to receive the MMR vaccine and rely on vaccine coverage around them for protection, the CDC says. Even small lapses in coverage can result in large outbreaks of measles, which is highly infectious; following exposure, 90% of susceptible people develop the disease.
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The CDC reports that nine outbreaks accounted for about half the cases in the U.S.:
Transmission occurred in households, child care centers, shelters, schools, emergency departments, and at a large community event. The largest outbreak occurred among 21 persons in a Minnesota population in which many children were unvaccinated because of parental concerns about the safety of measles, mumps, and rubella (MMR) vaccine. That outbreak resulted in exposure to many persons and infection of at least seven infants too young to receive MMR vaccine.
The CDC recommends that all children get the MMR vaccine at age 12 to 15 months, with a second dose at 4 to 6 years. Adults with no immunity to measles are advised to get one dose of MMR vaccine; college students, health-care workers, frequent international travelers should get two doses. And anyone aged 6 months or older traveling internationally, particularly to measles-endemic regions, should be vaccinated before departure.