In 2009, a half-dozen doctors, epidemiologists and other high-level decision makers gathered inside a conference room at the Ottawa headquarters of the Public Health Agency of Canada for a meeting that would soon turn contentious.

The purpose of the meeting was to examine the latest measles vaccination numbers from across the country. But this new round of data was unsettling, prompting debate among those in the room who didn’t believe what they were looking at.

For centuries, measles had been a global scourge, killing an estimated 200 million people since the 1850s alone, while leaving some of its survivors deaf, blind or brain damaged.

But several decades of vaccination efforts had beaten the virus into submission. By the late 1990s, the case counts for measles in Canada had dwindled to the point that practising doctors with first-hand experience treating its telltale fever and rash were becoming a rarity.

Measles was officially eliminated in Canada in 1998, a symbolic moment that meant the virus no longer circulated freely among the population. By the end of the century, the World Health Organization was already discussing the possibility of global eradication within a generation, and debating the merits of preserving the virus inside secure labs for future research, or burning what remained of it and being done with measles forever.

But somewhere between then and the meeting in 2009, the picture changed dramatically.

The data being examined at PHAC headquarters showed vaccine coverage against the deadly disease was slipping to levels well below the 95 per cent of the population considered ideal to keep the virus at bay, opening the door for measles to proliferate if a case arrived from abroad. In fact, the rates were at their lowest since the government began compiling statistics.

Only 76 per cent of two-year-olds had received one dose of the measles vaccine, which was alarming on its own. This was a precipitous drop from the 97 per cent coverage recorded in 1994, and 92 per cent in 2002, the only other years for which data are available.

Even more concerning was the fact that just 69 per cent of seven-year-olds in 2009 had completed a second dose that is recommended for optimal immunity.

Multiple factors were at work: Like polio and small pox, a vaccine-preventable disease such as measles no longer struck fear into parents as it once had. And, as complacency set in, online conspiracy theories pushing debunked research helped foment vaccine hesitancy.

But there was another troubling problem being discussed. Inside the room, several of the experts worried the already low numbers weren’t accurate because of how the data was collected, which they believed was inflating Canada’s coverage levels, according to two people involved in the meeting.

The conversation turned darker: If the numbers were off, how bad was it? “You saw that decreasing coverage,” said Michael Garner, who was the agency’s senior epidemiologist in charge of measles surveillance at the time. “The thinking was, if the numbers are right, we’re in trouble. And we think the coverage might actually be lower than what’s being reported.”

The figures, in other words, were giving a false sense of security.

A Globe and Mail investigation found that long before Canada was stripped of its measles elimination status by the Pan American Health Organization last month – amid a deadly measles outbreak that has amassed more than 5,300 cases, killed two unborn babies, and now ranks as the country’s worst in decades – people inside public health feared the country was leaving itself exposed.

Interviews with five top public health experts involved in infectious diseases, and a review of internal agency reports that have never been released publicly, paint a picture of a system struggling to confront declining immunity rates as the virus, once vanquished, waited for a new opportunity.

Forced to rely on surveys that were unsophisticated, blunt tools to track vaccinations across Canada, the agency could not easily or effectively gauge how bad the problem was becoming. “It was an ongoing question,” said Dr. David Butler-Jones, the Chief Public Health Officer from 2004 to 2013, about whether the data on hand gave a true depiction of national immunity.

The Globe obtained confidential documents that show how public health officials were trying to stoke urgency inside the government about falling vaccination rates, including an internal study from 2010 marked “Not for distribution nor copy,” which plotted how Canada would look today if the polio vaccine had never been introduced in 1955.

A second document, an internal study that raised alarms about public health’s inability to deal with an anti-vaccine movement that was gaining unprecedented reach online, was yet another such warning.

Prior to losing its measles elimination status in November, Canada was one of 82 nations to have successfully halted the virus from circulating within its borders, a distinction that ended after 27 years.

But long before the country lost that standing, during the 2009 meeting, federal officials parsing the data worried conditions were forming for a major outbreak.

All it would take was a spark.

“I remember leaving that room and saying, ‘I think this is a pretty big deal,’” Mr. Garner said.

‘Incomplete, erroneous, or missing’

At the federal level, Canada tracks how protected it is from measles and other vaccine-preventable diseases by conducting surveys of a few thousand people across the country, then extrapolating their responses to the entire population.

The most significant of those surveys is the Childhood National Immunization Coverage Survey, or cNICS, which launched in 1994 and has been conducted every two years since 2009. By interviewing parents about their children, the national public health agency, in conjunction with Statistics Canada, attempts to estimate what overall coverage levels are, including how many have received their first measles dose by age 2, and then the second dose by age 7.

Survey candidates are selected from a Canada Revenue Agency database of families who apply for the Canadian Child Tax Benefit, which includes about 96 per cent of children in the country. Candidates are then contacted by phone or online and asked to answer a series of questions about vaccinations.

It is, as the survey acknowledges in its preamble, a best-guess, “a probability.”

This imperfect system was borne out of necessity, though, because the federal government for decades struggled to get consistent, anonymized data from the provinces and territories that would help form a national picture: the numbers were either incomplete or tabulated using methodologies that were incompatible with other jurisdictions. In some cases, provinces refused to provide any data at all.

It always seemed more difficult than it should have been.

“We had to use the coverage surveys because the data from the jurisdictions was so unreliable,” said Dr. John Spika, who was director of immunization for Health Canada in the 1990s and later for the Public Health Agency of Canada, between 2007 and 2013.

“The surveys were a way to try and get around that, have a standardized polling of what coverage rates were,” he said.

But the surveys were cumbersome, with lengthy lists of questions, and relied on reaching people at home.

“They would randomly call people and say ‘Are you vaccinated?’ And they would say yes or no,” Mr. Garner said. “And then if they said yes, they would get asked, when did you get the measles vaccine?”

That came with flaws.

Building an accurate data set based on people who are willing to participate in a survey about vaccination also doesn’t give true results. “That’s always an issue,” Dr. Spika said.

The problem is self-selection, which became an issue when the epidemiologists and doctors began parsing the 2009 data. When they looked at the falling numbers, amid a rise in anti-vaccine sentiment in certain segments of society, they began to suspect that someone who is unwilling to get the vaccine, or has neglected to for myriad other reasons, may not agree to participate in the survey. And if the data skews towards people who are vaccinated and willing to talk about it, it will show a rosier picture than may actually exist.

As the officials looked over the data, they realized that the response rates for the survey were extremely low, in the 50 to 60 per cent range, which was a red flag.

“If you aren’t vaccinated and you have the government calling, you’re less likely to want to participate, especially if you’re anti-vax, or you haven’t been vaccinated for whatever reason. Like if you’re a mom who’s like, ‘I’ve been so busy, I feel guilty.’ There’s a differential that is likely there,” Mr. Garner said.

There was also the possibility that people may not give honest answers, not wanting to own up to it. “It’s like all the people who don’t say they smoke when Stats Canada asks,” said Mr. Garner, who spent 13 years at the public health agency, including as a senior science advisor, before leaving in 2019.

The challenges inherent in gathering such data were also a concern. “So many people have unlisted numbers or don’t answer the phone,” said Dr. Spika. “It made the undertaking of these kinds of surveys next to impossible.”

Inside the room, some feared that they were overcounting positive responses, and with sample sizes of just a few thousand people used to represent the country, any such bias could skew the results.

They debated whether to even release the numbers, or to go back and do more surveys.

“They didn’t release it for a long, long time,” Mr. Garner recalls.

The risk of relying on such methods to track underlying coverage trends, Dr. Butler-Jones said, was a delayed awareness of where weak spots in the population were hiding: “We’d be slow in recognizing it in a survey as opposed to having an ongoing database where you can actually pull up, you know, how many two-year-olds have not had their first dose or whatever.”

Dr. Butler-Jones referred to the surveys as: “Lots of estimates.”

Responding to detailed questions from The Globe, Health Canada and PHAC acknowledged the concerns with the surveys.

“While national vaccine coverage surveys do have limitations, they remain essential tools because they provide standardized, population-level estimates that cannot be obtained from any single administrative or digital source,” PHAC spokeswoman Anna Maddison said in an e-mail.

The agency said it recognizes some of the problems with the method.

“Surveys can be subject to recall and self-reporting bias,” she said. That is, memory problems or intentional misrepresentation.

Such inaccuracies could plausibly lead to artificial swings in the numbers up or down, Ms. Maddison said. Mr. Garner, however, said experts worried primarily about the risk of over-estimations, given how the surveys worked.

To verify information from people who respond, the surveys sometimes cross reference data against patient-held yellow vaccination cards, which are filled out by hand by healthcare providers or parents themselves. That also comes with concerns.

“Parent-held vaccination records may be incomplete, erroneous or missing some information,” the agency acknowledges.

Small sample sizes in some less-populated provinces and territories, owing to the problem of “survey fatigue” in those places, also present problems for assembling reliable data, Ms. Maddison said.

However, for all their weaknesses, the agency believes the surveys have value beyond trying to gauge coverage levels. PHAC adds additional questions to the process to gather data on peoples’ attitudes, beliefs and knowledge about vaccines, “including reasons for non-vaccination,” which registries can’t do, Ms. Maddison said.

Dr. David Heymann, a renowned epidemiologist who has led eradication efforts for polio and smallpox for the World Health Organization and was part of the WHO team that detected the first Ebola outbreak in 1976, said anonymized surveys are, by their nature, too general.

“It’s a macro,” said Dr. Heymann. “It tells you an area where there is a lower-than-normal coverage. But it doesn’t tell you who in that area is not vaccinated and so you can’t really identify those people. You can just treat the whole macro area as one that needs higher, more motivation to get vaccinated.”

Mr. Garner said inside the department there was pushback against the survey system. “There were enough people who were like, it’s expensive and it’s fraught with error,” and that epidemiologists wanted more precise tools.

When the public health agency’s outgoing Chief Public Health Officer Theresa Tam issued her final annual report this year, it too contained concern about Canada’s survey methods.

“Some national surveys may not recruit a sufficient number of respondents,” Dr. Tam said, and that the process may not “accurately represent some populations, such as people whose first language is not English or French.”

Mr. Garner said scientists at PHAC were concerned that response rates for the survey were too low to produce trustworthy data. The 2015 child vaccination survey had a response rate of just 50 per cent, for example. The Adult National Immunization Coverage Survey, or aNICS, which estimates coverage for people over age 18, has had response rates as low as 11 per cent, records show.

Amid this uncertainty, researchers have attempted workarounds to more accurately track the state of Canada’s measles protection at a national level.

In 2022, a group of 17 prominent Canadian doctors and epidemiologists conducted a different kind of survey, known as a serosurvey, which examined blood samples collected between 2009 and 2013 from more than 11,000 Canadians to check for the antibodies that indicate immunity to measles. The specimens were taken from Statistics Canada’s biobank, a repository that stores blood from about 22,000 Canadians who agree to let their anonymous samples be used in research.

The study, the first of its kind in Canada, found that only an older segment of the population – women in the 40-59 age bracket and men and women in the 60-79 group – met the 95 per cent threshold recommended to achieve herd immunity. Other age groups fell below that mark, with boys and girls aged 12-19 the lowest, with just under 79 per cent immunity.

Dr. Shelly Bolotin, director of the Centre for Vaccine Preventable Diseases at the University of Toronto who was one of the study’s authors, said serosurveys can serve as a compliment to coverage data, because they measure actual immunity to measles, which can come through either a vaccine or previous infection.

In this year’s measles outbreak, 93 per cent of cases in Canada occurred in individuals who were unvaccinated or had unknown vaccine status.

“Serosurveys provide a current, or recent, snapshot of immunity, which may not be concordant with coverage estimates collected years ago,” Dr. Bolotin said.

Dr. Natasha Crowcroft, also one of the study’s authors who was Senior Technical Adviser for Measles and Rubella at the WHO at the time, and is now Acting Chief Public Health Officer at PHAC, said serosurveys can also be used to detect if immunity in protected people is waning over time, which regular surveys can’t do.

But serosurveys are expensive, and therefore not routinely performed.

“We need to use many different sources of information to get a complete picture of how well Canadians are protected,” Dr. Crowcroft said in an e-mail to The Globe.

In their conclusion, the authors of the 2022 study issued a warning: “Population immunity to measles in Canada may not be sufficient to sustain elimination, particularly with ongoing measles importations from abroad.”

That study proved prescient. Two years later, when a measles outbreak began in New Brunswick in the fall of 2024, brought from an infected traveller from Thailand who flew to Canada for a wedding, it lit the fuse of a crisis. The spread began in communities with low vaccination rates, then moved across the country, finding areas of weakness along the way.

Since then, parts of Ontario and Alberta became the hotspots for measles in the Western Hemisphere, with 5,300 cases recorded nationwide by early December, including the deaths of two infants who contracted the virus in-utero and were born prematurely.

By comparison, before the outbreak began in late 2024, Canada had 12 measles cases in 2023 and three in 2022, linked to international travel.

Low immunity was the gateway allowing the virus to spread through the population. But unreliable data, wrought by an unreliable survey system, helped to cloak the precise decline in coverage over the years, blurring how exposed the country was.

Dr. Ronald St. John, an epidemiologist who ran the Pan American Health Organization’s infectious disease control programs in the 1980s and later became Director for Emergency Preparedness and Response at PHAC before his retirement, said the loss of Canada’s measles-free status is a wake-up call.

“If you lose it, it’s kind of shameful,” Dr. St. John said. “Especially for a country like Canada. Here, we should be doing better.”

A problem solved, a crisis forgotten

In late 2010, the Public Health Agency of Canada embarked on a confidential exercise, which was hypothetical in nature. Analysts within the department were tasked with a thought experiment: “What if we did not eliminate polio in Canada?” Internally it was meant to send a message within the federal government on vaccine-preventable diseases like measles if not kept in check.

The Globe obtained a draft copy of the document, which was not to be distributed outside the agency. The study aimed to depict how Canada would look had the polio vaccine not been developed in the 1950s and the paralysis-causing disease still circulated freely.

The goal was “to identify opportunities for public health action” on other diseases, the document said. It was also to demonstrate what the financial and societal stakes would be if polio had never been brought under control, said Dr. Butler-Jones, who agreed to talk about the document.

“It really was to help guide our planning and the kind of things that we need to focus on. And what the benefit of that could be,” he said.

“It was a like a fire drill on some levels,” Mr. Garner said.

A century earlier, newspaper headlines in Canada described a mysterious disease stalking children. Known for centuries as “lameness” before it was given a name, polio was deadly and could render its victims paralyzed, usually in the legs and respiratory muscles. This threat led to the advent of the iron lung, an oxygen chamber designed to help stricken patients breathe.

The effects also lingered; 25 to 40 per cent of adults who contracted any form of paralytic polio during childhood developed post-polio syndrome as adults, including loss of muscle function, atrophy and pain from long-term nerve damage.

After a vaccine was introduced in 1955, Canada’s last cases of polio resulting in paralysis occurred in the late 1970s in Alberta, B.C., and Ontario, and were traced to an earlier outbreak in a vaccine-hesitant community in the Netherlands. Canada and the Americas were certified polio-free in 1994; today, imported cases are rare.

If polio had never been curtailed, the internal PHAC scenario study describes a disease running rampant, flaring up at least once a decade with a major outbreak, and causing the healthcare system to buckle.

“In the absence of any other means of active polio immunization, all Canadian children, as well as adults, would have remained vulnerable to wild poliovirus infections and the threat of paralytic disease on an epidemic scale,” the report says.

Polio would have an enormous burden on Canada’s economy and quality of life, as well as the healthcare system, the report says. “The costs greatly exceed those costs attributed to the maintenance of elimination of polio.”

According to the report, the annual price tag for immunizing Canadian children against polio was approximately $58.9-million at the time. That is less than 2 per cent of the projected financial toll if polio hadn’t been controlled. That would add at least $3-billion a year in costs to the healthcare system, the document says.

Dr. Butler-Jones believes the fallout would have made the Canadian healthcare system unrecognizable, bending under each successive outbreak, not to mention the long-term health effects on the population.

“I’m convinced that all the orthopedic surgeons would be dealing with post-polio. They wouldn’t be doing hips and knees,” Dr. Butler-Jones said. “Also, the pain and suffering that ensues, and the lost productivity.”

Within government, the report was designed to serve as a reminder: a problem solved is a crisis forgotten. Polio may no longer be the threat it once was, but the healthcare system couldn’t handle it coming back in full force.

Dr. St. John sees an echo in measles today.

“One of my aunts lost her eight-year-old child to polio,” he recalls. “Was well and three days later was dead. That was a bad time. People understood how bad that disease was. I think they need to understand how bad measles is.”

‘The damage is done’

A second internal report obtained by The Globe was also designed to raise alarms within government. It showed a public health agency that was losing the battle against social media and the online world.

Produced in 2012, the “Emerging Global Realities Scenario Analysis Project” was an effort to put problems the agency was facing under a microscope, forecasting out 20 years – to 2032 – to predict future risks to the health and wellbeing of Canadians.

The report contained a warning, describing a trend that wasn’t fully grasped by experts at the time: the growing ability of anti-vaccination groups to find community online and amplify their message for new audiences.

“Populations can have greater influence than individuals. However, 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,” the internal report said.

There would always be a segment of the population that would refuse the vaccine, which public health wouldn’t be able to convert. The risk was the spill-over effect into others who might grow fearful and reluctant.

“Behaviours that were previously considered small niche groups of low impact might expand rapidly beyond the ability of public health to respond effectively.”

In 1998, the same year Canada achieved measles elimination, British researcher Andrew Wakefield published a study in the prominent medical journal, The Lancet, alleging the MMR vaccine, inoculating against measles, mumps and rubella, was linked to autism. The paper drew immediate rebuke from the scientific world for its spurious claims and haphazard connecting of dots. Deemed a fraud, the paper was formally retracted in 2010, a stain on The Lancet’s reputation. But it gained traction among vaccine opponents.

Scientists and researchers dismissed the fallout, believing the disgrace of having it debunked would be enough to relegate its claims to the waste bin of history. But the internet and, later, the rise of social media in the 2000s gave it an amplified means of recirculation, sowing doubt and mistrust of the vaccine that had brought measles to heel.

“A variety of factors all came together: great success; no disease; a new piece of information that was false that began to change public perception,” said Mr. Garner, who was one of 10 authors of the internal 2032 scenario paper at public health.

Though the study raised alarms about the emerging problem, he said the agency didn’t see just how formidable a foe the online world would be.

For years, officials knew one of the biggest opponents to disease eradication would be vaccine hesitancy – whether among pockets of religious objectors or other communities who refused the shot for a variety of reasons, or among those who believed the discredited Wakefield research.

But those groups only represented a few percentage points in the coverage data. And they were spread apart, geographically and culturally: the religious communities tended to be insular, and vaccine opponents, or those afraid of getting the shot, generally weren’t clustered in large numbers.

“We didn’t anticipate the impact it would have on people’s behaviour enough,” Mr. Garner said of the influence of social media. “And then when we saw the initial signs that there was this change in behaviour, this decrease in vaccination coverage, we didn’t react fast enough.”

“I think you had to fight fire with fire. We weren’t meeting the narrative. We were still trying to appeal to reason and social good and all those things.”

Dr. St. John also believes the public health system should have been more aggressive.

“Go out there and say things like, ‘This disease will kill your kid,’” Dr. St. John said. “Some people are a bit worried about saying things that way. But if other people are yelling, ‘This vaccine will cause autism,’ you’ve got to counter that.”

Not everyone can be convinced to change their mind, but dispelling misinformation “takes time and energy,” Dr. Butler-Jones said. “And there aren’t a lot of resources in public health.”

The job has gotten more complex as the Canadian government monitors seismic shifts under way at the U.S. Centers for Disease Control under Secretary of Health and Human Services Robert F. Kennedy Jr., a noted vaccine opponent.

The internal PHAC paper from 2012 doesn’t mention measles by name, but it predicted some of the biggest risks facing Canadian public health in 2032 would be “managing information and misinformation” amid “possibly a shrinking and less cohesive public health support system.”

That future came quicker than the authors predicted.

“I could go onto the street and say, ‘Does the measles vaccine cause autism?’ and you would find people who say yes. And there’s just no evidence. It’s not based on anything truthful,” Mr. Garner said.

“As much as that Lancet report was retracted, the damage is done.”

‘Needlessly complicated’

When the Chief Medical Officer of Health for Ontario, Dr. Kieran Moore, published his annual report this fall, he issued a call for a national vaccine registry in Canada so that the country could accurately track coverage, and spot weaknesses or gaps in the system. No more piecemeal data stitched together to form a best-guess composite view of national immunity.

Ontario is one of two provinces that require measles vaccinations to attend school, with exemptions allowed in certain cases (the other is New Brunswick), which gives it the ability to glimpse anonymous coverage data at a more local level. But Ontario also uses a patchwork of different systems, and has trouble integrating some vaccine data without duplicating entries.

“Modern immunization programs require comprehensive immunization data registries,” Dr. Moore wrote.

It would have been a cri de coeur for the public health system had it not merely been the latest in a long line of calls to create such a registry amid failed attempts to make it happen.

Dr. Spika remembers trying to build a workable version of a federal registry as far back as the 1990s, not long after he arrived at Canada’s Laboratory Centre for Disease Control in the summer of 1989 (PHAC was born in 2004 after the SARS crisis exposed weaknesses in Canada’s patchwork of provincial public health systems).

Dr. Spika had come to Canada from the US. Centers for Disease Control and was surprised at how many barriers were built into the Canadian system.

Because healthcare is the domain of provinces – as are vaccination programs – the federal government had minimal power. Outbreaks don’t respect provincial or national boundaries, but Canada’s system seemed beholden to them.

“In one case, there was an outbreak and I was trying to figure out what happened and I was told by a provincial epidemiologist, in so many words, keep your blankety-blank hands out of my jurisdiction,” Dr. Spika said.

In 1998, he attempted a project where the provinces would share anonymous vaccination data with Ottawa, “and we could actually then monitor what was going on better in the provinces,” he said.

The idea, dubbed the Special Public Health Information Exchange, or SPHINX, fell apart amid complications over funding, data transferability – provinces don’t use similar systems of formats – and debates over legal and privacy concerns.

“Unfortunately, it was too far ahead in terms of its concept,” Dr. Spika recalled.

Five years after the death of SPHINX, the federal National Immunization Strategy, a program in 2003 that was to be a blueprint for Canada’s vaccination efforts, also called for a national database. It was never created.

Later, as Canada’s first Chief Public Health Officer, Dr. Butler-Jones attempted to build a makeshift registry for vaccine coverage by adapting a system built for sharing information between Canadian laboratories.

“We actually had a kind of nice little elegant system we developed within the agency and we used it with the labs,” he said. “We were hoping to extend it into an immunization registry that everybody could use.”

But the idea became knotted up in territorial wrangling and debates over privacy that made it impossible.

“It’s getting the governments onside, the lawyers onside. It’s always easier to say no,” he said.

Federal funding under the Stephen Harper government was later directed toward a registry initiative known as Panorama, which was continued under the Trudeau government.

But that system hasn’t received buy-in from all provinces, with some complaining about its complexity and lack of adaptability to their own systems. Panorama, which cost $147-million of federal money to create, tracks routine childhood immunization. But there were gaps.

“In many jurisdictions, not all immunization providers, such as physicians and pharmacists, are required to report all vaccines administered, which affects the completeness of registry data,” said Ms. Maddison, spokeswoman for PHAC.

It was the most ambitious attempt yet for Canada to solve an age-old problem.

“They were going to unify everything into one data set to rule them all in Canada,” said Mr. Garner, the former measles epidemiologist at PHAC. “Panorama was supposed to do this – and Panorama failed.”

“We just seem to have made it needlessly complicated,” Dr. Butler-Jones said.

The federal government is now at work on a new attempt, called Standardized Reporting on Immunization, or STARVAX. In this iteration, now being tested, provinces and territories produce standardized reports out of their own databases that are fed up to the national system, “so results are comparable and can be combined,” Ms. Maddison said.

It gives provinces more control but it relies on buy-in. To date, only five provinces and one territory (Alberta, Saskatchewan, Manitoba, New Brunswick, Nova Scotia and Yukon) submit to STARVAX. Quebec has agreed to join, but has yet to begin reporting. B.C. said its data won’t be fully integrated until 2026.

However, some provinces say they can’t adopt the new system. PEI, for example, says it calculates immunization rates differently than STARVAX. Different methodologies would cloud the data, “which would create confusion for decision makers and members of the public,” said Morgan Martin, a spokeswoman for the PEI government.

Though only a partial picture of the country, STARVAX is meant to complement the surveys, giving the federal agency a more detailed glimpse of coverage than it previously had – but the system remains a work in progress.

Meanwhile, concerns about the accuracy of the coverage surveys persist.

For example, the most recent child vaccination survey available, from 2021, reported that 79.2 per cent of seven-year-olds in Canada have received the two doses recommended for full immunity to measles. It is a low number, but Ontario reported an even smaller figure for that same year – 66 per cent – in its provincial database. The province attributed the weaker coverage in part to the COVID-19 pandemic when children weren’t seeing their doctor, or didn’t have access to one.

As well, the Adult National Immunization Coverage Survey, which tracks people 18 years and up, is sporadic in its reporting: The most recent version showed 87.4 per cent of adults had at least one dose of the measles vaccine. The only other time that survey has been released, in 2008, the number was far lower, at 71.2 per cent. PHAC cautions both data sets are largely based on the ability of adults to recall their status.

Better data systems are key for fighting future outbreaks, said Dr. Heymann, who is based in London, U.K. Ideally, they move beyond anonymized data to allow entire countries to mount focussed campaigns to bolster coverage for dangerous diseases. Such databases exist in the U.K., he said.

Dr. Spika, who left Canada in 2001 to work for the WHO in Europe before returning to PHAC in 2007, said European countries with disparate healthcare systems have managed to reach data-sharing agreements that have led to versions of anonymized registries. “It can be done,” he said.

For Dr. St. John, it’s unacceptable Canada hasn’t solved the problem after decades of trying.

“You should think in this day and age, we should be able to cobble it together,” he said.

When asked about concerns among doctors and epidemiologists about inaccurate surveys giving a muddled picture of Canada’s protection against diseases like measles, Dr. St. John replied: “All true.”

Cases ongoing

In a statement following Canada being stripped of its measles elimination status last month, the Canadian Medical Association said it was deeply concerned and disappointed by the development.

“For more than 25 years, we collectively held measles at bay. We can do it again,” the CMA said.

If Canada is to regain that designation, which is bestowed on countries that have halted domestic circulation of the virus for at least a year, it will take time and considerable work to bolster the country’s systems.

In addition to stopping domestic transmission, one of the steps the Pan American Health Organization recommends Canada undertake to regain its status is to consolidate electronic immunization registries across the country.

Meanwhile, new cases of measles are still being recorded by the week, though in smaller numbers than during the summer.

Dr. Butler-Jones said Canada worked hard to earn its measles free status in the late 90s. “And then once you get there, you forget what it took to get there and take it for granted,” he said.

Looking back, Mr. Garner wonders what might have been different.

“What we’re seeing now is this sustained transmission in the population because the population’s coverage is so low. And it’s been clear that we’ve been headed that way for years,” Mr. Garner said.

“If the data from the survey was 100 per cent accurate, would it have created more of a response? For some reason there just wasn’t this alarm.”