Outbreak of measles in an unvaccinated population, British Columbia, 2014

Background: Although Canada eliminated endemic measles in 1998, outbreaks are expected to occur periodically through import-related transmission in geographically clustered unvaccinated communities. In the spring of 2014, in association with an outbreak in the Netherlands, a large measles outbreak occurred in British Columbia in a community unvaccinated for religious reasons. Methods: Case finding with assistance of the local community, its school and religious leaders and local health care providers was conducted to identify confirmed, probable and suspect cases. Measles control guidelines were implemented with limited uptake of measles-containing vaccine (MCV) but higher adherence with infection control measures and travel restrictions. Results: A total of 433 cases (325 confirmed and 108 probable) were identified. Rash onset ranged from February 22 to June 9, with 98% during March and April. Fifty-seven percent of cases were students of one school. The median age of cases was 11 years and 68% of cases were aged five to 19 years. Ninety-nine percent of cases were unvaccinated. One case had encephalitis and recovered. Only five cases occurred outside of the affected community. Genotyping results were consistent with importation from the Netherlands outbreak. Conclusion: This outbreak in a community with low-vaccination rates affected largely the pediatric-age population, compatible with acquisition of measles immunity by adult members due to prior wild-type measles infection. Although vaccine hesitancy persisted in this population, containment of the outbreak was facilitated by a high degree of community cooperation with infection control measures and restriction of movement.