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Measles outbreak continues in Canada, even among immunized population
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BOSTON — The measles outbreak in Canada continues to occur in both vaccinated and unvaccinated individuals and is causing concern over vaccine effectiveness, according to a presentation here during the IDSA 49th Annual Meeting.
“While this still ongoing outbreak feeds largely on unvaccinated individuals, the high proportion of cases who received two doses raises concerns on vaccine effectiveness,” Philippe Belanger, MSc, Ministère de la santé et des services sociaux du Québec, Montréal, told Infectious Diseases News, “However, the take-home message is still to get vaccinated.”
Two mass campaigns were implemented in Quebec in 1996. The goal of the first was to administer a second dose of measles vaccine to children aged 18 months to 16 years, and the goal of the second was to introduce a two-dose measles vaccine schedule in young children (at 12 and 18 months). The first initiative resulted in an 89% coverage rate for the second dose. Despite these efforts, Belanger said that Quebec is experiencing the largest measles outbreak reported in the Americas since 2000.
Between Jan. 1 and Aug. 3, 2011, 727 cases were reported; 682 meet the national case definition and 35% of those were laboratory confirmed. Prior to mid-March, the few sporadic cases were linked to importations from Europe, but there was continued transmission that peaked in May, and the cases declined after the end of the school year in late June. However, cases continued to persist through Aug. 3.
Measles has been reported in 10 of the 18 regions of Quebec province. Two of those regions account for 71% and 20% of all cases, respectively. Just over 2% of the cases have been acquired outside Canada, and those came mostly from France (13/15), according to Belanger.
The mean age of cases was 15 years, with the highest incidence among 10- to 19-year-olds (65%). Incidence then decreased to 21 per 100,000 in preschoolers and to 14 per 100,000 in 5- to 9-year-olds.
The incidence among 20- to 39-year-olds was 4 per 100 000, which the investigators believe is because they were largely included in the 1996 mass campaign. Only 12 (1.8%) cases were in individuals older than 40 years.
Almost 12% of cases resulted in hospitalizations, with the highest rates among children aged 12 to 17 months (29%) and adults aged 30 years and older (27%).
Overall, 66% of cases were considered to have occurred in unvaccinated individuals: 24% had written proof of vaccination and 10% reported being vaccinated without a written proof. In 5- to 19-year-olds, 21% had written proof of measles vaccination (17% had two doses and 4% had one dose), and an additional 10% reported being vaccinated without a written proof.
Disclosures: Dr. Belanger reports no relevant financial disclosures.
For more information:
- Belanger P. #LB-33. Presented at: IDSA 4th Annual Meeting. Oct. 20-13, 2011. Boston.
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