Assessment of population immunity to measles in Ontario, Canada: a Canadian Immunization Research Network (CIRN) study

Abstract

Canada eliminated measles in 1998. We conducted a sero-epidemiology study to estimate population immunity to measles in the province of Ontario, Canada and to identify groups at higher risk of outbreaks. We used a previously developed modified enzyme immunoassay to test 1,199 residual sera from patients aged 1–39 years. We re-tested negative and equivocal sera using a plaque reduction neutralization assay. We interpreted our results in the context of Ontario’s immunization program and vaccine coverage data. Of 1,199 sera, 1035 (86.3%, 95% confidence interval (CI) 84.4, 88.2) were above the measles threshold for protection, 70 (5.8%, 95% CI 4.5, 7.2) were equivocal and 94 (7.8%, 95% CI 6.3, 9.4) were negative. The proportion of positive sera was highest for those 1–5 years, with 180/199 (90.5%, 95% CI 86.4, 94.5) positive sera, and lowest for those age 12–19 years, at 158/199 (79.4%, 95% CI 73.8, 85.0). Adjusted for age, females were more likely than males to have antibody titers above the threshold of protection (odds ratio = 1.60, 95% CI 1.14, 2.24). Most of the study cohort were eligible for two measles vaccine doses, and vaccine uptake in Ontario is >90% for school-aged cohorts. We observed a higher than expected proportion of sera with antibody levels below the threshold of protection, suggesting that immunity in some Ontario age-groups may be waning, despite high vaccine coverage. Alternatively, the traditional measles correlates of protection may not be an appropriate measure of population protection in measles-eliminated settings.

Population immunity to measles in Canada using Canadian Health Measures survey data – A Canadian Immunization Research Network (CIRN) study

“…1) is consistent with a previous study of measles seroprevalence in Ontario (Canada’s most populous province) performed by our group, which found that 79.4% of samples in the 12–19 age-group were positive (Supplemental Fig. 2) [14] . For specimens obtained from Quebec, seroprevalence for this age-group in the current study was 76.5%, and may explain the large measles outbreak that occurred in Quebec in 2011.…”

“…During this same period, there have been increasing reports of measles importation into Canada from abroad [11] , [12] , causing local outbreaks. Furthermore, there is now compelling evidence that vaccine mediated immunity is less robust than immunity from previous infection [13] and can wane over time [14] , [15] , [16] , [17] , [18] . Waning immunity (i.e.…”

“…Waning immunity (i.e. secondary vaccine failure) is particularly problematic in settings that have eliminated measles [14] , [15] , [16] , [17] , [18] due to the lack of immunological boosting from circulating virus. The combination of sub-optimal vaccine uptake, waning vaccine-mediated immunity and ongoing importations from measles endemic jurisdictions abroad presents a critical challenge to sustaining measles control.…”

Gender differences in measles incidence rates in a multi-year, pooled analysis, based on national data from seven high income countries

“…There is evidence of a weaker antibody response to measles vaccine in boys [ 41 ] and a higher humoral antibody response to live measles vaccine in females has been observed in young adults [ 42 ]. There also appears to be less waning in immunity to measles vaccine in females [ 43 ]. Thus, even after immunization, males may be more susceptible to measles than females.…”

Long-term waning of vaccine-induced immunity to measles in England

“…Occasional outbreaks were also reported in highly vaccinated groups 7,8 , leading to concerns over waning of measles immunity among adults vaccinated during their childhood 9 . Immunological studies from Canada 10 , Japan 11 , and Czechia 12 pointed towards waning of antibodies in young adults who had been vaccinated more than 20 years prior, while no decrease was observed in previously infected individuals 13 . Young vaccinated adults had little exposure to measles in near-elimination settings, showing that waning of vaccine-induced immunity may be related to the time since the end of endemic transmission 14 .…”