Journal of Infectious Diseases
15 November 2009  Volume 200, Number 10
http://www.journals.uchicago.edu/toc/jid/current

Major Articles and Brief Reports
VIRUSES
Long–Lasting Measles Outbreak Affecting Several Unrelated Networks of Unvaccinated Persons

Frédéric Dallaire, Gaston De Serres, François-William Tremblay, France Markowski, and Graham Tipples

Abstract
Despite a population immunity level estimated at 95%, an outbreak of measles responsible for 94 cases occurred in Quebec, Canada. Unlike previous outbreaks in which most unvaccinated children belonged to a single community, this outbreak had cases coming from several unrelated networks of unvaccinated persons dispersed in the population. No epidemiological link was found for about one-third of laboratory-confirmed cases. This outbreak demonstrated that minimal changes in the level of aggregation of unvaccinated individuals can lead to sustained transmission in highly vaccinated populations. Mathematical work is needed regarding the level of aggregation of unvaccinated individuals that would jeopardize elimination.