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Measles epidemiology

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Excerpt from the report of the Comité d'immunisation du Québec’s Measles Task Force

“Use of a second dose of measles vaccine and intervention during outbreaks”
July 1994.

Measles is one of the most contagious of all diseases. Before vaccination programs were introduced, virtually everybody contracted it. Because measles is so highly contagious, children were quickly infected and 99% of them had had the disease by the age of 15. The annual number of cases in urban settings was estimated at 95% of the number of births. The disease was endemic, with epidemic peaks every three to five years. Between 1955 and 1970 in Québec, reported incidence was well below actual incidence, varying from between 58 and 319 cases per 100,000 head of population.

Commercialization of attenuated live vaccine in the mid-1960s provided an effective tool for preventing the disease. Prior to 1970, the vaccine was used on a small scale by family doctors and pediatricians, but no data are available to show what proportion of the population had access to it. Québec officially introduced its vaccination program in January 1970. The vaccine was given to children aged 5 and under who had not yet had measles. As is still the case in 1994, it was recommended that the vaccine be administered as soon as possible after a child’s first birthday.

Following the vaccine program’s introduction, the incidence fell but outbreaks continued to occur in Québec in 1970 (79/100,000), 1973 (73/100,000), 1980 (58/100,000) and 1984 (20/100,000). Each of these outbreaks was lower in intensity than the last. In December 1988, a few cases appeared in the Montréal region and in early 1989 a very large outbreak quickly spread to all regions of Québec. It led to over 10,000 reported cases, including five deaths and four cases of meningoencephalitis. The overall incidence was 152 per 100,000 inhabitants – the highest reported rate since 1967 (168/100,000). It affected the following age ranges, in decreasing order of magnitude: children aged between 10 and 14, (962/100,000), infants from 0-1 (591/100,000), and teenagers aged 15-19 (390/100,000).

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