Large Outbreak of Measles in a Community with High Vaccination Coverage: Implications for the Vaccination Schedule

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Abstract
Background. Attempts to eliminate measles from a country or region may be disrupted by an imported case that affects indigenous persons. The objective of this study was to analyze epidemiological and clinical characteristics of a measles outbreak in Catalonia, Spain, in 2006. Methods. Data on cases of measles reported to the Department of Health, Generalitat of Catalonia, during the period 28 August 2006 through 8 July 2007 were collected. Suspected cases were confirmed by determination of measles-specific immunoglobulin M antibodies and/or detection of virus genome. Incidences were calculated using the estimated population of Catalonia for 2006, and 95% confidence intervals were determined assuming a Poisson distribution. The association between proportions was determined using the χ2 test and Fisher's exact test. The level of statistical significance was set at a=.05. Results. A total of 381 cases were confirmed, for an incidence of 6.6 cases per 100,000 persons. A total of 89.5% of cases occurred in nonvaccinated persons, mainly those aged ≤15 months (incidence, 278.2 cases per 100,000 persons; mean age of patients, 12 months). Indigenous subjects accounted for 89.8% of cases, and laboratory confirmation of results was obtained for 87.1%. Measles genotype D4 was identified in all sequenced samples. Conclusions. The age distribution of cases of measles among children aged ×15 months suggests that the first dose of vaccine should be routinely administered at the age of 12 months.