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International Notes Update: Measles -- Canada, 1986

Between January 1, and April 12, 1986, 7,941 measles cases in Canada were reported to the Laboratory Centre for Disease Control, a greater than 20-fold increase over the corresponding period in 1985, and the largest number of measles cases reported since 1979 (Figure 1). Eight provinces reported more cases during this period than during the same period in 1985 (Table 3). British Columbia, Manitoba, and Nova Scotia accounted for 63%, 21%, and 11% of the total cases, respectively. The overall incidence rate for Canada was 31 cases per 100,000 population. British Columbia experienced the highest incidence rate (174/100,000 population) followed by Manitoba (153/100,000) and Nova Scotia (102/100,000).

Age data are available for 5,260 (98%) of the 5,367 cases reported in Canada during the first 2 1/2 months of 1986 (Table 4). Thirty-six percent of cases occurred among 10- to 14-year-olds; 29%, among 15- to 19-year-olds; and 21%, among 5- to 9-year-olds. The highest incidence rate (104/100,000) occurred for 10- to 14-year-olds. The rate for 15- to 19-year-olds and 5- to 9-year-olds was 77 cases and 61 cases/100,000, respectively. In 1985, 10- to 14-year-olds also had the highest incidence rate (45/100,000).

Investigations of some of the current outbreaks in British Columbia and Manitoba indicate that approximately 73% and 55% of patients, respectively, had histories of measles vaccination. Although most patients have histories of receiving live measles vaccine, the proportion who received adequate immunization (according to current definitions) is not known. Further epidemiologic investigations are ongoing. Of interest is that, in British Columbia, between 1969 and 1974, half-doses of live measles vaccine were administered to conserve vaccine supply. In addition, many children in Canada may have received further attenuated live measles vaccine and human immune globulin simultaneously, or live attenuated measles vaccine within 6 weeks after immune globulin, killed vaccine, or vaccine at under 12 months of age. Reported by P Varughese, S Acres, Laboratory Centre for Disease Control, Ottawa, Ontario, Canada; Div of Immunization, Center for Prevention Svcs, CDC.

Editorial Note

Editorial Note: Measles vaccine of several types, including inactivated vaccine, has been used in Canada since 1964 (1). All provinces now routinely use further attenuated measles vaccine combined with mumps and rubella (MMR), which is recommended for use at or after 12 months of age (2). The mean annual measles incidence rate decreased from 358 cases/100,000 during the prevaccine era (1949-1958) to 30/100,000 during 1976-1985, a 92% reduction. The highest rate during the past 10 years was in 1979--95/100,000 in 1979. The lowest reported incidence occurred in 1983--4/100,000.

Measles elimination has been a priority since the early 1980s in all provinces (3). Ontario, New Brunswick, and Manitoba, representing 43% of Canada's population, introduced legislation in 1981, 1982, and 1985, respectively, making measles vaccination compulsory for school entry. Provinces without school immunization laws have used intensive education efforts to encourage vaccination and report that over 95% of children are vaccinated by the time they reach school age. The current measles outbreaks in Canada are probably attributable to accumulation of susceptibles due to unvaccinated school-aged children who started school before widespread use of measles vaccine in Canada, persons inappropriately vaccinated, and vaccine failures.

Large numbers of U.S. tourists travel to Canada each year, and more tourists than usual are expected this year because of Expo '86. Because of the large measles epidemics in several provinces of Canada, it is advisable that travelers to these areas be immune to measles. Recommendations for travelers to Canada are essentially the same as those for travelers to any area where measles is endemic or epidemic (4). A physician's documentation of prior measles disease, measles vaccination (on or after the first birthday), or laboratory evidence of immunity constitutes evidence of immunity. In the United States, measles vaccine is recommended for all children 15 months of age or older. However, the age at vaccination should be lowered for those children traveling to areas where measles is endemic or epidemic. Children 12-14 months of age may receive MMR before their departure, with no need for revaccination. Children 6-11 months of age may receive single measles antigen vaccine (without rubella or mumps antigens) before departure but must be revaccinated with MMR vaccine. The optimal age at revaccination is 15 months, although the age at revaccination may be as young as 12 months if the children remain in high-risk areas.

References

  1. Larke RP. Impact of measles in Canada. Rev Infect Dis 1983;5:445-51.

  2. National Advisory Committee on Immunization, Health and Welfare, Canada. A guide to immunization for Canadians. Ottawa, Ontario, Canada: Minister of Supply and Services, 1980.

  3. White F. Policy for measles elimination in Canada. Rev Infect Dis 1983;5:577-82.

  4. CDC. Recommendations for measles vaccination for international travel. Advisory memorandum no. 85, March 12, 1986.



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