Measles antibody seroprevalence rates among immunized Inuit, Innu and Caucasian subjects

Abstract

Measles antibody seroprevalence was compared in Innu, Inuit, and Caucasian peoples of northern Newfoundland, Canada, who were immunized with a single dose of M–M–R–II (Merck Research Laboratories) vaccine. Healthy, volunteer schoolchildren ( n=606) were enrolled. Measles antibody was measured with a whole virus measles-specific IgG EIA. Native (Innu and Inuit) schoolchildren ( n=253) had a significantly higher seropositive rate (83%) after a single dose of measles vaccine compared to Caucasian ( n=353) children (76%; p=0.025), and higher mean antibody levels after immunization compared to Caucasian children (1.74 EIA units, vs. 1.63; p=0.06). Caucasian children were more likely to have been immunized after age 15 months (20.6% vs. 9.6%; p=0.001). There was no significant difference in the mean time interval between immunization and blood sampling for natives versus Caucasian (8.0 years vs. 7.95 years; p=0.49). After adjustment for time from immunization and age at immunization, there remained a marginally significant racial difference in seropositivity (OR=1.65, 95% CI 0.96, 2.83, p=0.068). The unadjusted odds ratio for seropositivity (comparing natives vs. non-natives, combining negative and equivocal results) was 1.66 (95% CI 1.06–2.59, p=0.018). The higher measles-seropositive rate found among native compared to non-native Canadian children suggests that genetic and/or environmental factor(s) affect circulating antibody levels following immunization. The determination of these sources of variability may lead to the development of more efficacious vaccines or delivery strategies.