Canada’s public health system faces a significant challenge as declining immunity rates threaten the country’s hard-won status of measles elimination. Experts have expressed concern that without properly tracking vaccination coverage and population immunity, we risk a return of measles. This disease had almost been eradicated in Canada since the country reached elimination in 1998. The challenge is compounded by poor survey methodology and a lack of national data provided by provinces and territories.
As noted by Dr. Natasha Crowcroft, the Acting Chief Public Health Officer at the Public Health Agency of Canada (PHAC), it is critical that we conduct serosurveys. These surveys are key for monitoring population immunity over time. These seroprevalence surveys give a good picture of actual immunity levels in the community, whether from vaccination or past infection. “It really was to help guide our planning and the kind of things that we need to focus on,” said Dr. Butler-Jones, emphasizing the importance of reliable data.
Throughout the years, Canada became accustomed to low case counts of measles, particularly following the 1998 elimination declaration. This success was marred by the discredited research of British doctor Andrew Wakefield, who falsely linked the MMR vaccine to autism in a fraudulent study. This paper, published in the same year as Canada’s elimination, was retracted in 2010 but left a lasting impact on public perception of vaccines.
In 2021, these statistics indicate that just 79.2 percent of seven-year-olds in Canada have received their required two doses of the measles vaccine. This shows a troubling gap in vaccination coverage among young children. As a result, vaccination rates have plummeted. In 2015, only half of parents answered child vaccination questionnaires, down drastically from 71.2 percent in 2008. Dr. Theresa Tam, the outgoing Chief Public Health Officer, expressed concern about these declining response rates in her final annual report, noting that “some national surveys may not recruit a sufficient number of respondents.”
Effectively measuring vaccination coverage is no easy task. This is exacerbated by the fact that unvaccinated people and vaccine-skeptical people are more likely to drop out of surveys, adding an additional wrinkle to the method. Mr. Garner pointed out that “if you aren’t vaccinated and you have the government calling, you’re less likely to want to participate.” This hesitance results in underreporting and colors the data.
Dr. David Heymann, an epidemiology luminary and leader of WHO’s health emergency program, took traditional anonymized surveys to task. He emphasized the power of individual behavior to shape population level health results. “Populations can have greater influence than individuals,” he stated. He warned that “more than ever before, individuals are now able to more effectively and rapidly cluster around an issue or cause and exert the influence of a population.”
Dr. Shelly Bolotin noted that it’s critical to figure out better ways to collect data. In addition, she suggested that serosurveys might complement and improve the existing coverage data. “They would randomly call people and say ‘Are you vaccinated?’ And they would say yes or no,” explained Mr. Garner about traditional survey methods, highlighting their limitations.
The PHAC has struggled to obtain consistent anonymized data from various provinces and territories, hampering efforts to monitor immunity levels effectively. Dr. Spika tried to make a workable federal registry work as far back as the 1990s but ran into numerous roadblocks.
