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Somerset Street West at Queen Elizabeth Drive is seen in Ottawa, on April 25, 2020.

Justin Tang/The Canadian Press

After one week on the job, members of the federal government’s new immunity task force say they are coming to grips with a towering wall of uncertainty that obscures the true extent of COVID-19 in Canada.

With more than 50,000 confirmed cases across the country and likely many more that have gone unreported, scientists are certain there is a population of individuals in Canada that have acquired some level of immunity to the new coronavirus that causes COVID-19. What remains unclear is the size and makeup of that population, the level of immunity it has developed and for how long.

The answers have a huge bearing on what comes next – not only in the short term once physical distancing measures are relaxed, but over a much longer period before the widespread deployment of a vaccine, during which time Canadians will be trying to conduct business and live life in the ever-present company of a new and still poorly understood health risk.

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As a report released on Thursday by the University of Minnesota’s Center for Infectious Disease Research and Policy makes clear, the characteristics of the coronavirus and past experience with influenza pandemics suggest that recurrent waves of COVID-19 are a strong possibility in the coming months. If so, a clearer picture of immunity in Canada will be instrumental for public-health agencies deciding how to respond if infections begin to rise.

“I think there’s a direct relationship to how we move forward, given the relevance of background immunity to the speed at which new waves of virus can spread through the population,” said David Naylor, task force co-chair and former president of the University of Toronto.

The stated focus of the task force, which had its first meeting on Tuesday, is to accelerate that picture with a series of population surveys that measure rates of exposure to the virus, ideally within a matter of weeks. Longer-term studies will also be conducted to determine the duration and biological underpinnings of immunity to COVID-19.

PANDEMIC WAVES

Three possible scenarios for COVID-19 are based on past flu pandemics. The first scenario shows an initial wave followed by a series of peaks that diminish in height as population immunity builds. In the second scenario, a larger wave develops in fall and winter, similar to what occurred during the 1918 flu pandemic. The final scenario, which was not seen with past flu pandemics but is still considered possible for COVID-19, features a less pronounced pattern of varying infection levels after the initial wave.

Scenario 1: Peaks and valleys

COVID-19 cases

2020

2021

2022

Scenario 2: Fall peak

COVID-19 cases

2020

2021

2022

Scenario 3: Slow burn

COVID-19 cases

2020

2021

2022

SOURCE: CENTER FOR INFECTIOUS

DISEASE RESEARCH AND POLICY

PANDEMIC WAVES

Three possible scenarios for COVID-19 are based on past flu pandemics. The first scenario shows an initial wave followed by a series of peaks that diminish in height as population immunity builds. In the second scenario, a larger wave develops in fall and winter, similar to what occurred during the 1918 flu pandemic. The final scenario, which was not seen with past flu pandemics but is still considered possible for COVID-19, features a less pronounced pattern of varying infection levels after the initial wave.

Scenario 1: Peaks and valleys

COVID-19 cases

2020

2021

2022

Scenario 2: Fall peak

COVID-19 cases

2020

2021

2022

Scenario 3: Slow burn

COVID-19 cases

2020

2021

2022

SOURCE: CENTER FOR INFECTIOUS

DISEASE RESEARCH AND POLICY

PANDEMIC WAVES

Three possible scenarios for COVID-19 are based on past flu pandemics. The first scenario shows an initial wave followed by a series of peaks that diminish in height as population immunity builds. In the second scenario, a larger wave develops in fall and winter, similar to what occurred during the 1918 flu pandemic. The final scenario, which was not seen with past flu pandemics but is still considered possible for COVID-19, features a less pronounced pattern of varying infection levels after the initial wave.

Scenario 1: Peaks and valleys

COVID-19 cases

2020

2021

2022

Scenario 2: Fall peak

COVID-19 cases

2020

2021

2022

Scenario 3: Slow burn

COVID-19 cases

2020

2021

2022

SOURCE: CENTER FOR INFECTIOUS DISEASE RESEARCH AND POLICY

“We want to get a sense of how that background immunity is growing and which populations are a real priority for testing,” Dr. Naylor said.

A key tool for measuring potential immunity is serological testing, which does not detect the presence of the virus but can reveal if the body has formed defensive antibodies against COVID-19, a process that is typical by three weeks after infection.

Catherine Hankins, a professor of public and population health at Montreal’s McGill University who co-chairs the task force, said that a limiting step in measuring the extent of immunity to the coronavirus within Canada has been determining which serological tests are sensitive and reliable enough to provide good data. In its first week, an important first priority for the task force has been working with the National Microbiology Laboratory in Winnipeg to validate the performance of tests and to set standards for research teams deploying tests across the country.

“The sooner we can have a good solid test with very high sensitivity and high specificity [to the virus], the sooner we can move forward," Dr. Hankins said.

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But task force members cautioned that it’s not yet known how much immunity is conferred by exposure to the virus or for how long. This makes it unlikely that merely testing for exposure would serve as an “immunity passport” enabling individuals to get back to life as it was before COVID-19, as some have suggested.

Dr. Hankins was also quick to dispel another notion that has been making the rounds on social media: that the virus will naturally die out if it is allowed to spread and build up herd immunity, the level of total immunity within the population.

“It’s not going to happen just by letting it run wild … and you would lose a lot of people along the road," she said.

In such a scenario, COVID-19 would likely become a permanent fixture, constantly circulating through the population as the birth rate provides a steady supply of new hosts. This may happen in any case, but long before a large share of the population is exposed, the virus is liable to surge again and again, placing renewed strain on health care systems in the process.

To gauge the risk of this happening, researchers need more data as soon as possible on the number of unreported cases of COVID-19 in Canada, including the unknown fraction that are asymptomatic.

Mona Nemer, Canada’s chief science adviser and also a task force member, said that based on discussions with counterparts in other countries, estimates of the number of unreported cases vary widely from a few times to as many as 100 times the confirmed. Without a better handle on this, projecting the impact of any strategy other than strict physical distancing will be reduced to guesswork.

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“It makes a huge difference in terms of how you manage the disease, and manage living with the disease,” Dr. Nemer said.

This week the task force began discussions with teams that are looking to shed light on the prevalence of asymptomatic cases by taking advantage of existing infrastructure for sampling, such as through blood donors. While such groups are not entirely random – for example blood donors do not include children and are made up of a healthier-than-average subset of the population – the data that could be quickly gleaned from such samples would constitute an important start, Dr. Naylor said.

Task force members said that more information was needed on immunity in different populations, to shed light on racial and socioeconomic factors that may be related to infection. And a large geographic difference is expected between urban and rural areas based on population density.

Another important result from population surveys will be the degrees of immunity in relation to the severity of the disease. It is not yet clear, for example, if someone who has experienced a mild or asymptomatic case and who has formed some antibodies to the virus will be as immune as someone whose experience with COVID-19 was more pronounced.

This week, the task force also discussed protocols for studies that track segments of the population to see how long immunity may last. Currently, almost nothing is known about this because the coronavirus is such a recent arrival in the population. Immunity to coronaviruses that are already endemic to the human population and that cause colds every year may only last for months. If the virus that causes COVID-19 proves similar, then it is effectively here to stay, as demonstrated in a modelling study published last month in the journal Science.

In contrast, the 2003 SARS virus was shown in studies to confer immunity for at least three years, a scenario that would vastly improve chances for controlling and potentially eliminating COVID-19. In that case, experts have noted, the spike of population immunity that follows the first year or two of the pandemic may offer the best and perhaps the only chance to wrestle it to the ground.

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“That’s why we really do have to bank on a vaccine for this,” Dr. Hankins said.

Now that it is recommended you wear a face covering in dense public settings like grocery stores and pharmacies, watch how to make the three masks recommended by the Centers for Disease Control and Prevention. Written instructions available at tgam.ca/masks The Globe and Mail

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