Robust Measles Immunity in British Columbia’s Lower Mainland
Researchers found robust immunity to measles among people living in the Lower Mainland of British Columbia, indicating high uptake of the measles vaccine in the general population.
Fran Lowry, Medscape October 16, 2025
Measles seropositivity was 89% overall in a sample of more than 1000 sera taken from patients who had gone to local laboratories to have their blood tested.
“We have seen reports of measles vaccine coverage as low as 80%, but it has to be kept in mind that those reports assume that people whose vaccine status is unknown are unimmunized. That is not an accurate reflection of the true proportion of the population that has been vaccinated,” senior author Danuta Skowronski, MD, a physician at Immunization Services at the BC Centre for Disease Control in Vancouver, told Medscape Medical News.
The findings were published on October 14 in CMAJ.
| Variation by Age |
Most measles cases in recent years have occurred among unvaccinated patients, said Skowronski. “If we had coverage as low as 80%, we would be having rip-roaring measles epidemics everywhere. Measles is that infectious: It’s one of the most highly infectious viruses that we know,” Skowronski said.
To assess the risk for measles transmission throughout the community at large, the investigators analyzed more than 1000 serum samples obtained from outpatients (age, 1 to > 80 years) who were attending a laboratory network in British Columbia’s Lower Mainland, the most populous region of the province, in August 2024.
“This [finding] shows that most parents know the importance of vaccinating their children and are getting their kids vaccinated,” Skowronski said.
However, measles antibody levels were lower in older children and young adults. In children aged 10-19 years, seropositivity was 82%. In 20- to 29-year-olds, it was 69%, and in 30- to 39-year-olds, it was 73%.
Virtually all adults older than 55 years had detectable measles antibodies, but less than 75% of adults aged 20-39 years had them.
Publicly funded measles vaccination for children aged 12 months has been routine since 1969. In 1996, a second dose at age 18 months was added. In 2012, the second dose was rescheduled to age 4-6 years.
“The lower antibodies in that young adult age group likely reflect age-related waning of vaccine-induced antibody, which is potentially exacerbated by their having received a first dose at 12 months of age and having been born to previously infected mothers,” Skowronski said.
Vaccination may not always be documented in immunization registries, underscoring the need for the reliable capture of this crucial information, she added.
| Reassuring Results |
“It is relatively comforting knowing that in general, at a population level, that the seroprevalence is hovering around the 90% range,” Isaac Bogoch, MD, infectious disease physician and professor of medicine at the University of Toronto in Toronto, told Medscape Medical News.
“This is for a population in the Lower Mainland of British Columbia, so you cannot extrapolate to the entire country, but it does gives us a window into the seroprevalence of measles antibodies in a community and I think that’s really helpful.”
One concern is the lack of strong provincial vaccine registries, said Bogoch. “Some places don’t have them and we don’t have a national vaccine registry, so when we look at uptake of vaccinations, we know that the data we’re looking at do not necessarily reflect the true vaccine uptake. Studies like this help provide an understanding of what our risk is for vaccine-preventable illness outbreaks in the country.”
The findings have a certain predictive value. “If we have greater than 90% of the population immune to measles, it tells us that large-scale and widespread outbreaks are much less likely. Outbreaks will be more focal, where there are large pockets of unvaccinated individuals, rather than widespread across a large swath of the population,” said Bogoch.
“The study’s results are consistent with previous studies conducted in Canada at the provincial or national level showing high population immunity overall, with lower seropositivity in younger age groups that are immune through vaccination,” Shelly Bolotin, PhD, director of the Centre for Vaccine Preventable Diseases at the University of Toronto’s Dalla Lana School of Public Health, told Medscape Medical News.
“This phenomenon is a hallmark of measles-eliminated settings, where measles virus does not circulate endemically and humoral immunity is therefore not boosted,” she added.
The authors acknowledged that measles seropositivity requires nuanced interpretation in the context of elimination. “Although low seropositivity estimates in population subgroups may cause alarm, it is important to note, as the authors have done, that seronegativity in vaccinated individuals or in a highly vaccinated population (as in this case) does not necessarily indicate susceptibility because vaccinated individuals can mount an anamnestic response to measles exposure. This point is evidenced in the epidemiology of recent measles cases in British Columbia, where, despite low seropositivity in some groups, only 5% of cases were vaccinated. This suggests that this population meets the measles herd immunity threshold,” Bolotin concluded.
| The study was funded in part by the Public Health Agency of Canada. Skowronski, Bogoch, and Bolotin reported having no relevant financial relationships. |
Source Medscape
| References |
Also see
Measles immunity 90% in British Columbia’s Lower Mainland, finds study Medical Xpress
Measles Surging in Ontario Medscape
Northeast B.C. measles vaccinations below herd immunity as school resumes, health officials say
