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
Larke RP. Impact of measles in Canada. Rev Infect Dis
1983;5:445-51.
National Advisory Committee on Immunization, Health and
Welfare,
Canada. A guide to immunization for Canadians. Ottawa,
Ontario,
Canada: Minister of Supply and Services, 1980.
White F. Policy for measles elimination in Canada. Rev Infect
Dis 1983;5:577-82.
CDC. Recommendations for measles vaccination for international
travel. Advisory memorandum no. 85, March 12, 1986.
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