Revaccination of children during school-based measles outbreaks: potential impact of a new policy recommendation.

Abstract

To evaluate the potential impact of revaccination on measles outbreak control during school-based epidemics. Retrospective cohort study. Thirty-two public elementary and high schools in 14 communities on the west island of Montreal. All 19,439 children attending these schools during the 1989 measles epidemic in Quebec. After notification of a case children with provider-verified records of vaccination on or after their first birthday were identified; the remaining children were vaccinated or excluded from school. Clinical or confirmed measles cases not prevented by this intervention that could have been prevented had revaccination been included during the outbreak. Of the 88 measles cases (74 confirmed) proof of one adequate vaccination was present in 48 (55%). Intervention generally occurred within 5 school days after case notification. The nonpreventable cases involved 75 children who had measles onset before the intervention and 11 (7 vaccinated) who had onset within 8 days after the intervention. The two remaining cases occurred 20 and 25 days after the intervention among nonvaccinated students who refused to be vaccinated. Except for these two cases measles was eliminated at every school. Application of the new Canadian guidelines for measles outbreak control would have required the administration of at least 10,000 additional doses during the outbreak to students vaccinated before 1980; implementation of the new US guidelines would have required the administration of 16,629 additional doses to children previously vaccinated only once. Well-enforced provincial regulations ensuring vaccination of every student upon school entry might have prevented 38 (43%) of the cases. The US recommendation of two routine doses of vaccine before school entry might have prevented 86 (98%) of the cases. However, revaccination during the outbreak would not have prevented a single additional case. Revaccination of previously vaccinated students during a measles outbreak would have been costly and of little benefit.