By John G. Bartlett, MD
Measles is on the upswing in the United States. This Viewpoint examines the trend in the context of a recent update from the Centers for Disease Control and Prevention on the first 7 months of 2008.
Update: Measles -- United States, January-July 2008
MMWR Morb Mortal Wkly Rep. 2008;57:893-896
This CDC report reviews 131 cases of measles occurring in January-July 2008. The following points should be noted:
This is the highest year-to-date number of measles cases in the United States since 1996.
Of the 131 cases, 91% were persons who were unvaccinated or who had an unknown vaccination status.
123 were US residents, including 80% under age 20; 112 were unvaccinated or had unknown vaccination status; 95 of these 112 (85%) were eligible for vaccination, and 63 of these 95 (66%) were unvaccinated because of philosophical or religious beliefs.
During this time, 2 outbreaks were reported. The first outbreak, in Washington State, included 7 children in 1 household and 19 additional cases linked epidemiologically. The possible source of the outbreak was a church conference. The second outbreak was in Illinois and involved 4 unvaccinated girls followed by 26 additional measles cases that were epidemiologically linked to these 4, making a total of 30 cases. Of these, 29 of the children were home-schooled, not subject to school-entry vaccination requirements, and had parents who rejected vaccinations.
The authors note that the United States had an average of 450 reported deaths from measles and 4000 cases of measles encephalitis annually before the availability of measles vaccine in the mid-1960s. Public health experts claim that sustaining the elimination of measles requires that more than 90% of children in preschool and 95% of school-age children be vaccinated. The measles vaccine coverage in the United States is adequate to sustain this goal; a problem surfaces when susceptible children travel abroad and import cases from Europe and other regions of the world. When these children return to the United States, they transmit measles to other vulnerable, unvaccinated children by passing the herd-immunity threshold. Those who are susceptible also include children under age12 months, who are too young to be vaccinated. The obvious recommendation is for parents to ensure childhood vaccination according to current guidelines; adults without evidence of measles immunity should receive a single dose of MMR vaccine, and travelers should be up-to-date on measles vaccination.