RISK-FACTORS FOR MEASLES AND VACCINE EFFICACY DURING AN EPIDEMIC IN MONTREAL

Objectives: 1) to identify potential risk factors for measles and 2) t o assess the efficacy of the measles vaccine. Methods: Cases of measle s reported from primary and secondary schools in Montreal during the 1 989 epidemic were compared with classroom and sibling controls with re spect to age at vaccination against measles, time since vaccination, t ype of vaccination, type of providers and age of the mother. Results: Subjects vaccinated at 12 months had an OR of 3.9 (CI 95%: 2.1 to 7.0) of contracting measles when compared with subjects vaccinated at 15 m onths or later. Vaccination at age 13 or 14 months was not associated with an increased risk. Subjects vaccinated before June 1979 had an OR of 5.8 (CI 95%: 2.8 to 12.1) of developing measles compared with subj ects vaccinated after June 1980. Vaccine efficacy was 96.1%. Discussio n: In highly vaccinated populations, vaccination at 12 months and vacc ination before 1980 are probably two reasons why outbreaks still occur . The two-dose schedule could reduce the proportion of vaccinated pers ons who remain susceptible.