In British Columbia’s Lower Mainland, a recent study published in the Canadian Medical Association Journal reveals that 90% of the population has detectable antibodies against measles. This indicates robust vaccine coverage and substantial population protection in the region. The findings come at a critical time as measles cases have surged across North America, with Canada reporting over 4,000 cases by August 2025—a fivefold increase compared to any full-year tally since achieving measles elimination status in 1998.
Measles, known for its high infectivity, requires a herd immunity threshold of approximately 92% to 94% to prevent widespread transmission. The study highlights that individuals born before 1970 are generally considered immune due to past infections during endemic circulation. In contrast, those born after rely on vaccine-induced immunity, with two doses of the measles vaccine recommended in British Columbia—administered first at 12 months and again between 4 to 6 years of age.
Understanding the Current Immunity Landscape
Public health officials have raised alarms over increasing vaccine hesitancy, which could potentially undermine vaccine coverage. The study’s findings are based on blood samples collected in August 2024 from over 1,000 individuals in the Lower Mainland, British Columbia’s most populous region. Researchers discovered measles antibodies in about 90% of participants, with particularly high coverage among young children: 92% to 94% of 2- to 3-year-olds and 97% of 4- to 6-year-olds had antibodies, reflecting the high uptake of first and second vaccine doses.
However, the study also noted lower antibody levels in older children, particularly those who were due for their second vaccine dose during the COVID-19 pandemic. Among adults, virtually all aged 55 years or older had detectable antibodies, but this figure dropped to less than 75% among those aged 20 to 39 years.
Expert Insights and Implications
The study’s authors suggest that the decline in detectable antibodies among younger adults may result from several factors, including the natural decrease of vaccine-induced antibodies over time. This effect might be more pronounced in individuals vaccinated as infants born to mothers who had natural infections. Despite this, vaccinated individuals without detectable antibodies may still possess some level of protection due to other immune system components.
“The observed epidemiology in BC and elsewhere in Canada indicates that current levels of population immunity are sufficient to suppress sustained or generalized measles transmission,” writes Dr. Danuta Skowronski of the BC Centre for Disease Control and the University of British Columbia. “This is supported by measles outbreaks that have been sporadic, self-limited, or centred on linked and largely nonvaccinated individuals or communities.”
The findings underscore the importance of maintaining high two-dose vaccine coverage to ensure continued measles elimination. The study also highlights the need for efficient and accurate systems to document vaccine doses, as serosurvey results showed higher antibody presence than vaccine coverage estimates suggested.
Looking Ahead: Strategies for Measles Elimination
The study’s authors advocate for periodic population-based serosurveys within a public health context. These surveys can clarify vaccination coverage estimates, inform catch-up vaccination strategies, and support overall measles elimination efforts.
“Our findings highlight missed documentation of administered measles vaccine doses and reinforce the importance of efficient and accurate systems to capture and confirm 2-dose coverage,” the investigative team concludes. “Periodic population-based serosurveys can clarify estimates of vaccination coverage, inform vaccination catch-up and other program adjustments, and support measles elimination efforts overall.”
As public health officials continue to combat vaccine hesitancy and strive for high immunization rates, the study provides a reassuring snapshot of measles immunity in British Columbia’s Lower Mainland, while also pointing to areas for improvement in vaccine documentation and outreach.
