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Background: In 1989 a second dose of measles vaccine was recommended for US children to prevent school outbreaks of measles. Coverage of school age children with a second dose remains incomplete, and data on the effectiveness of this recommendation are limited. We investigated a measles outbreak in Mesa County, CO, in December, 1994, and evaluated the efficacy of preoutbreak immunizations at an elementary school (School A) where many students had received two doses., Methods: All reported suspected cases of measles were investigated; cases that met a clinical case definition were tested by a measles IgM antibody assay. A confirmed case required laboratory confirmation or had to meet the clinical case definition and be epidemiologically linked to a confirmed case. Vaccination records of students at School A were reviewed. The effectiveness of one and two doses of measles vaccine was estimated using logistic regression., Results: Sixty-two confirmed cases were reported, including 17 at School A. At School A the attack rate in unvaccinated children (7 of 16, 44%) was higher than in those with 1 dose (10 of 320, 3%) or 2 doses (0 of 289, 0%). Estimated vaccine effectiveness was 92% for 1 dose and 100% for 2 doses. Two doses were better than one dose in decreasing the likelihood of acquiring measles (P = 0.003)., Conclusions: The lower attack rate among two dose recipients provides evidence that a two dose strategy can help prevent measles in schools. Administering the second dose at elementary school entry can help prevent the persistence of susceptible cohorts of children and is likely to be important in sustaining elimination of indigenous transmission of measles in the United States.

Objectives: To describe patterns among imported measles cases to the United States., Design: Descriptive analysis of national case-based surveillance data on measles cases., Setting: United States in the period 1986 through 1994., Patients: All reported confirmed cases of measles., Main Outcome Measures: Demographic variables, immunization history, country of exposure, and reporting state., Results: The number of reported imported cases of measles to the United States has dropped from an average of 99 cases annually in 1986 through 1988 and 190 cases in 1989 through 1991 to 61 cases in 1992 through 1994. Since 1990, the number of imported cases originating in Latin America declined by 98%, despite continued increase in the number of travelers to this region; cases from other regions remained relatively constant. This decrease paralleled the rapid decrease in measles incidence in the Western Hemisphere associated with national measles elimination programs. Most imported cases occurred among children, although 22% of cases occurred among young adults. Rates of measles cases per 1 million travelers are higher among non-US citizens than among US citizens., Conclusions: The sharp decline in importations into the United States from Latin America since 1991 provides evidence of the success of measles control efforts undertaken there. The decrease in imported cases has been associated with a decline in total measles cases in the United States. Sustained elimination of measles in the United States will require improved measles control in other countries in addition to a high level of population immunity.