From October 24, 1996 to June 1, 1997, 482 cases of measles were reported from 103 public schools in Riyadh, Saudi Arabia. Standard measles control policy for School Health Units (SHU) was to promptly vaccinate with MMR all students in schools with a measles case. However, operational constraints limited this effort. We evaluated the impact of this vaccination strategy during the outbreak.
Methodology
Daily reporting of date of onset of the all cases of measles in the school, the date of vaccination of school children, the number of students enrolled in 44 schools by class were ascertained. We calculated the attack rate (AR) of measles, the preventable fraction (PF%) relative to vaccination within 5 days, and the corresponding 95% confidence interval (95% CI) for each 10 day delay in vaccination after the onset of the first case.
Results
The measles AR in the affected schools was 6.1 per 1000 students. SHU were able to vaccinate all students in 14 (31.8%) schools, a variable numbers of students in six (13.6%) schools, and no students in 24 (54.6%). The vaccination campaigns began a median of 14 days after the date of diagnosis the first case of measles in the school (range 0-56 days). In fully vaccinated schools vaccination within 10 days after the onset of the first case yielded a PF% of 59.5% (95% CI 40.6-72.4) which decreased to 0% (95% CI 0.0-32.7) for a delay of 12 days or over, after the onset of the first case. In schools where selected groups were vaccinated within 10 days after the onset of the first case the PF% was 55.6 (95% CI 21.1-75.9) decreased to 0% (95% CI 0-27) for a delay of 12 days or more after the onset of the first case.
Conclusion
Prompt vaccination of the students in the first 10 days after the onset of the first case is an effective method of controlling measles outbreaks within schools. However, it has many logistic constraints and is not easily practiced. The alternative strategy, which could be more easily applied is routine vaccination of teenagers in high school.