After canada began to emerge, in 2003, from the spring outbreak of the severe acute respiratory syndrome coronavirus—sars-CoV, first of its name—Ross Upshur thought it might be worthwhile to study public perceptions about quarantines. At the time, he was a family physician at Toronto’s Sunnybrook Hospital who, thanks to his background in public health, had found himself in charge of enforcing the quarantine of hundreds of people; all told, more than 25,000 people in the Toronto area were kept isolated for ten-day stretches in their homes. Upshur understood that the practice raised plenty of ethical issues: Was it a proportionate response to the risk? Did restricting individual freedoms prevent a greater harm to society? Could the government ensure that the needs of those in isolation would still be met? But he was also curious: Just how bad did Canadians think it was to violate a quarantine order? Was it like running a stop sign? Was it like roughing someone up? Was it like . . . killing them?

The Canadians surveyed back then gave the question some thought, and a full half of them concluded that, yes, breaking quarantine was the equivalent of manslaughter. An additional 27 percent compared it to felony assault. “We were shocked when we got the results,” Upshur says. “We went, ‘Holy crow, Canada is really bullish on quarantine!’”

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Over a decade later, this bullishness has served the country well in its far more difficult fight against the far more infectious sars-CoV-2. Canadians have, by a significant majority, been very supportive of the widespread distancing measures required to bring the pandemic under control. Once the entire country had the distinct experience of sheltering in place for months, though, and once places like Germany and New Zealand declared the first phase of this long pandemic behind them, we turned antsy and started eyeing the exits. Unfortunately, shutting a nation down is considerably easier than opening it back up. Politicians and public health officials are attempting to figure out, in real time, just what it takes to safely emerge from an extended state of mass quarantine—and what exactly life will look like over the twelve or eighteen or twenty-four months that may still stand between us and a vaccine.

Even health economists, who model epidemic-mitigation strategies, are working in uncharted territory with sars-CoV-2, the virus that causes the illness of covid-19. “A lot of the pandemic plans around the world are based on influenza, where you don’t need to develop a whole new vaccine,” so containment measures can be more nuanced, says Beate Sander, Canada research chair in economics of infectious disease. As the h1n1 influenza virus spread in 2009, she helped produce a study that examined the costs of different interventions to curb the disease. “School closures were the wildest scenario we tried,” Sander says. “You couldn’t even think about the situation now, with covid-19—it [would have seemed] just so far out there.”

The introduction of restrictive measures in Canada seemed—like falling in love or going bankrupt—to happen slowly, then all at once. First travel alerts were issued, then schools were shut down, then states of emergency declared across provinces; within days, aside from the once-weekly grocery trips and two-metre-buffer strolls that turned us all into anxious geometers, those who weren’t essential workers just stayed home.

As the lockdown stretched on, however, excitement started to build around schemes that might get us out of it. Politicians, talking heads, news reports, and uncles on Facebook went through exuberant periods of discovery, touting the possibilities of antibody tests or immunity passports or contact-tracing apps that would ping if you had come too close to someone who later tested positive for covid-19. But the coronavirus pandemic is a complex, hydra-headed creature wreaking considerable havoc—3.3 million people infected worldwide in its first four months—and these strategies don’t amount to a silver bullet: some won’t work, some shouldn’t, and some can’t yet.

“It’s very difficult to know what to do in this type of situation,” Sander says. Comparisons to previous health emergencies offer limited guidance: although sars hit Toronto hard, it remained relatively contained around the world, while Ebola was not a respiratory illness. “With covid-19, you have a virus that spreads very easily, often among asymptomatic people, and can still cause quite severe disease,” Sander says. “I don’t have examples for how to go about relaxing interventions.”

“Everyone is looking for the cavalry to come,” Upshur says. “We want an approach that’s going to get us out of here quickly. But I’ve worked on pandemic preparedness since the mid-’90s. You learn one thing: respect the virus.”

When a new virus invades the human body, the two branches of our immune system set to work. First up is the innate immune system, the foundational protection against pathogens. “It recognizes that something foreign and noxious has entered our bodies, and it turns on all sorts of alarm signals,” says Jennifer Gommerman, a professor of immunology at the University of Toronto. The innate immune system generates antiviral proteins called interferons, which, fittingly, interfere with a virus in order to limit its ability to reproduce. While this system is critical, “it’s not exactly a special-ops team,” she says. “It’s more like a barrier that the immune system puts up to deal with the virus.” That barrier causes a ton of collateral damage: you get a fever, which helps power up the immune system to fight off infection, and are left feeling lousy.

Over time, this crude defensive effort gives way to the adaptive immune system, a more sophisticated response that emerges once the body has had a chance to learn about a virus and tailor its counterattack. We have a seemingly limitless repertoire of lymphocytes, the subtype of white blood cells that are fine-tuned to respond to the particular protein causing all the chaos. Those lymphocytes produce giant quantities of antibodies, which target a virus’s vulnerabilities, prevent it from hijacking host cells, and clear it from our system. The adaptive immune system also has the ability to remember that virus, so if you’re reinfected with it, your lymphocytes respond quickly and vigorously, generating immunity to the pathogen. The tricky bit is that, if your body has never seen a virus before—a virus, let’s say, like sars-CoV-2—it can take one to three weeks for those lymphocytes to start working.

The innate immune system is a sledgehammer: it assumes that a threat could spread anywhere. Quarantine is a sledgehammer too: it assumes the same about all of us. Most diseases circulating in our population have been around long enough that we’ve either acquired natural immunity, thanks to the long memory of our adaptive immune systems, or we’ve developed a vaccine. This way, when an outbreak occurs—as it did last summer with measles in Montreal—it unfolds against a backdrop of some existing immunity, so efforts to contain the spread can be more surgically applied to the individuals and places at risk. But no one had developed any immunity to sars-CoV-2 because no one had contended with this coronavirus before. “We very rarely see a completely susceptible population,” says Ashleigh Tuite, an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health. “That’s why we’re all hiding in our houses—because a very good way to keep the infected people away from the susceptible people is to keep everybody away from everybody else.”

But, also like the innate immune system, quarantine causes all manner of collateral damage. Nearly 6 million Canadians applied for covid-19 employment benefits in the first month of the pandemic alone. In some parts of the country, rates of domestic violence have risen as much as 30 percent. Close to 100,000 people had their surgeries cancelled or postponed in order to free up hospital beds for covid-19 patients, the cbc found. And half of us reported in a recent poll that our mental health had deteriorated as a result of the uncertainty and isolation. So, until a vaccine arrives, how can we build the equivalent of an adaptive immune system for covid-19—targeting our response only where it’s needed instead of everywhere at once? How do we trade the sledgehammer for a scalpel?

An older man looks out the window. Reflected in the glass are a cyclist and a pedestrian walking outside.

During the first wave of the pandemic, Canada, like most countries, followed the spread of covid-19 by testing people who had symptoms of the illness. That’s done through polymerase chain reaction (pcr) tests, which detect markers of the sars-CoV-2 genome in the genetic material collected in a nasal swab. pcr tests will be crucial throughout the pandemic to diagnose new cases of covid-19 because they identify traces of the virus while it is still present in our bodies—they tell us where the virus is now. But those traces vanish once antibodies have cleared it from our systems, so pcr tests neither reveal where the virus has been nor offer a picture of all the people who’ve had it.

For that, you need to look at a person’s blood serum through a serology test. These tests scour for particular antibodies to sars-CoV-2; the most refined of them can search specifically for antibodies that meddle with the interaction between the sars-CoV-2 spikes—the knobby, crown-like proteins that give coronaviruses their name—and receptors on the surfaces of our own cells. Determining how many people have developed antibodies illustrates the progression of sars-CoV-2 through a population, which is vital for establishing a more nuanced response to the disease.

That’s why, as restrictions loosened and focus shifted to managing covid-19 until the appearance of effective therapies or a vaccine, serological testing gained traction. The UK announced a large-scale study that aimed to test upwards of 20,000 people in its first wave and 300,000 within a year. In the Netherlands, where as many as 10,000 people donate blood each week, serological tests are now part of screenings. At the University of Toronto and Sinai Health, researchers across disciplines have collaborated on a robotic system that can detect the antibody response in up to 10,000 blood samples a day.

In each of these serological surveys, the goal is to monitor the virus’s prevalence within communities in order to better understand how immunity might be developing and how deadly covid-19 is proving to be. For all our talk about the curve, there’s an equally important shape in epidemiology: the pyramid of disease severity. Deaths are at the very top of the pyramid, followed by hospitalizations, then ER visits. Below that, there are the people who consult their doctors, and then, at the bottom, those who are sick but never seek medical care. “We see the more severe outcomes: the hospitalizations and the deaths,” Tuite says. “We’re less good at finding the less severe outcomes, which tend to be much more frequent.” Serological testing helps epidemiologists fill in the base of the pyramid so they can use that information to make more precise estimates of how many susceptible people remain.

But what if, policy makers mused, serology testing could benefit not just the community but recovered individuals as well? The idea—floated by countries including Germany, Italy, the UK, and Chile—is that a positive antibody test could locate the lucky citizens whose immunity would allow them to rejoin the workforce and anchor the economy while physical distancing continues. These individuals would qualify for an immunity passport, some sort of government-issued documentation that would permit them to leave the house, head into the office, or shop for groceries with zero concern about catching the illness.

In Canada, Kumanan Wilson, a specialist in general internal medicine at The Ottawa Hospital, has been investigating the ways proof of immunity might work here. Eight years ago, Wilson and his colleagues created the mobile national immunization app CANImmunize, and now he is collaborating with Canada Health Infoway, a federally funded nonprofit, to determine how best to issue digital certificates to people who are no longer susceptible to covid-19. “It would be almost like a boarding pass, with a scannable bar code that says you have the requisite lab results that identify you as immune,” Wilson says. That certificate could then be scanned before entry is granted to sports arenas, airports, or large gatherings. “When Trudeau says twelve to eighteen months for a vaccine, people are looking to whether there’s anything we can do before then,” Wilson says. “It’s a bit Orwellian—it’s not an ideal solution. But we’re not living in an ideal situation now.”

In early may, Swiss pharmaceutical giant Roche racked up international headlines when it revealed details of its sars-CoV-2 serology test—one far more promising than any yet on the market. Germany struck a deal to purchase 3 million of the tests that month and 5 million for every month that followed. The US Food and Drug Administration also cleared the test for emergency use. (Health Canada had not, by that time, approved the sale of any serology test.)

There are two ways to measure the accuracy of a serology test, and on both counts, Roche’s numbers are unmatched. For its sensitivity—how well the test identifies the people who have had sars-CoV-2 and developed antibodies to it—Roche says it works 100 percent of the time. That means there are no false negatives, where you have the antibodies but the test says you don’t. Still, says Brenda Fine, an instructor in the mathematics department at the British Columbia Institute of Technology, “that’s the kind of error we don’t care as much about. Someone is safe to go out, but we don’t send them.”

Then there’s the specificity of the test: how well it rules out the people who have not developed the requisite antibodies. Those are the true negatives. Roche claims a specificity of 99.8 percent, which means that 0.2 percent of the time, the test will give a false positive. “That’s the dangerous mistake,” Fine says. “Those are the people who, according to the test, are good to go to work, to a play, to a party, when they’re not safe at all.”

A 0.2 percent error rate sounds pretty good. But the extent of that mistake hinges on the prevalence of sars-CoV-2 in a population: how many people have or have had the disease. The lower the prevalence, the higher the number of false positives. In a community of 1 million people, for example, with a prevalence of 50 percent, 500,000 people would still be susceptible to the virus. Roche’s error rate means that 1,000 of them would get a false positive. When prevalence is 10 percent and 900,000 people are susceptible, 1,800 of them would be incorrectly told they have antibodies. When prevalence is 1 percent, that number rises to 1,980.

The greater the population, the worse the consequences. In a country of 40 million, with a prevalence of 1 percent, nearly 80,000 people would be under the mistaken impression that they were safe from covid-19. That’s why, however much we might all wish otherwise, serological tests can’t give any single person a clean bill of health or enable them to blithely bypass distancing protocols. The better the group fares—the lower the prevalence of the illness in the population—the less we’re in a position to know how any individual within the group will do.

“I’ve worked on pandemic preparedness since the mid-’90s. You learn one thing: respect the virus.”

So just how prevalent is this virus? The World Health Organization’s best guess for the global population is 2 or 3 percent. In Canada, we haven’t a clue. “Because the pcr testing was so poorly done, especially at the beginning, there are so many people who were asymptomatic and could have transmitted it,” says Anne-Claude Gingras, a senior investigator at Sinai Health’s Lunenfeld-Tanenbaum Research Institute. “We don’t know if we’re dealing with a prevalence of 0.1 percent or 1 percent or 10 percent.” Those people given false positives aren’t just risking their own health by rejoining the outside world—they’re well positioned to then spread the virus to others, causing new community outbreaks. The same thing that makes serological testing so crucial for a community makes it so risky for any one user to rely on its results. We’re still completely in the dark.

What’s more, prevalence is going to vary region by region, city by city: Canada might well have an average national immunity of 10 percent, but those rates will look very different in Vancouver, which was initially hit hard by the virus, and in Charlottetown, where cases are low. “At this stage, I don’t know why we’re talking about national policy,” Fine says. “That might be useful if we were thinking about flying across the country, but we’re still at the stage where we’re wondering if we walk to the store a kilometre away. This is something for cities to decide one at a time.” Upshur, now an epidemiologist at the University of Toronto’s Dalla Lana School of Public Health, agrees: “Most of the countries that have managed the pandemic have been islands or small populations,” he says. “Canada is so huge that this is going to have to be done on a local level.”

Even if we did manage to devise an absolutely iron-clad serology test, one that never returned false positives at all, it still wouldn’t be a perfect solution—because scientists don’t yet have any clear sense of how natural immunity to sars-CoV-2 works or how long it will last. “The immunity of respiratory viruses is extremely tricky,” Upshur says. “They mutate quickly and, for some reason, unlike measles or mumps, we don’t get this permanent, enduring immunity.” Immunity could perhaps last two years, as with the first sars; it could also be more like six months. We won’t know until we have the benefit of two, three, five years’ hindsight. “It’s really nice to think that serology is going to come to the rescue, but I’m not convinced it’s going to be the tool people think it is at the current time,” Upshur says. As for immunity certificates? There, he’s less inclined to hedge. “The idea that we would have anything like an immunity passport is science fiction.”

As the great plague advanced through seventeenth-century London, red-painted crosses sprouted on sealed wooden doors: the stamp of the infected. In 1940s Canada, yellow quarantine signs took their place, alerting passersby to the polio or whooping cough or diphtheria that lurked inside. Immunity certificates reverse the indicator—here, it’s the healthy who are marked. Maybe that’s enough to mean the idea “actually might have some merit, under certain circumstances,” as US National Institute of Allergy and Infectious Diseases director Anthony Fauci said in April. As politicians (both the elected and armchair kind) have argued, even in the absence of a foolproof test or a better understanding of the illness, this lockdown can’t continue indefinitely. Trade-offs need to be made: a little more covid-19, a little less economic pain. Does that tip the balance in favour of these passports?

Not when the effect would still be to divide families, workplaces, communities, and the country into two castes: the immune and the vulnerable. “You’ve introduced an ‘us’ and a ‘them’—you’re a vector of danger, you are to be feared, whereas I am the good, clean one,” says Françoise Baylis, a professor of bioethics at Dalhousie University. “That’s deeply problematic. It’s a bifurcation of the world.” It creates enormous ethical and social concerns.

To begin, it means that the prize for everyone who has faithfully obeyed the rules and avoided unnecessary contact—and therefore the illness—is that they must keep sheltering in place for some unknown period of time. “You went home from work, you took the financial hit, and now the government is setting a precedent that says, ‘Well, we’re glad you followed the rules, but you don’t get to go back to work because you haven’t been infected and you haven’t survived it,’” Baylis says. That also makes it difficult for public officials to come back at the outset of a new wave of cases and ask citizens to quarantine again. “Why would you do that the second time around? Why would you believe that you should?”

In a world where immunity is rewarded, there is every likelihood that some people would start to take chances with covid-19 not out of carelessness or frustration but as a conscious choice to contract it—that they would endanger their own health because they’ve been punished for their efforts to preserve it. “There are people who are particularly desperate to get back to work,” Baylis says. “If this is the only way, haven’t you created an incentive for them to get themselves infected?”

There’s also the not-inconsiderable dilemma of how a system like this would be designed and enforced. “Are you talking fines? Are you talking imprisonment? Are you going to spot-check? Is this going to be a visible or invisible system?” she asks. And how would you map out the deployment of the antibody test itself? Who, after essential health care workers and the especially vulnerable, would have first crack at them? How long would it take to roll something like this out? There’s no quick way to test nearly 40 million people, and when that test determines freedom of movement, the stakes are enormous. “We already know that there are all kinds of discrimination built into many of our public systems,” Baylis says. (Recall that, in March, the entire roster of the Brooklyn Nets was checked for coronavirus as symptomatic New Yorkers clamoured for testing.) “So the idea that it won’t be the wealthy, the powerful, and the elite getting access to serological tests—that’s just not the case.”

And yet, a return to some form of life is already underway. Since immunity certificates and at-home antibody tests can’t structure that return, what should? The answer is a three-part strategy that will shape much of our short- and medium-term future: test, track, isolate.

It demands, for starters, widespread testing—far more widespread than we have right now. Theresa Tam, Canada’s chief public health officer, said that, before any restrictions could be loosened, provinces and territories would need to be running 60,000 pcr tests a day, more than twice as many as they were able to in early May. It is not possible to fight this pandemic without testing both those who are already ill and the so-called silent spreaders, who can transmit the virus before symptoms kick in. It looks increasingly like there are a lot of them out there. After testing 6 percent of Iceland’s population—both those who felt sick and those who felt fine—researchers found that 43 percent of the people who tested positive were asymptomatic at the time.

Testing is the backbone of any country’s response to this pandemic. However, once a person receives a positive diagnosis for sars-CoV-2 and is safely placed in isolation—whether that’s in their own home, separate from other family members, or in a medical facility or designated recovery site—contact tracers must go to work. These trained public health employees feature prominently in the response to any communicable disease because they’re essential to identifying and then breaking chains of transmission; now, that means working with someone infected with covid-19 to pinpoint everyone they were exposed to in the forty-eight hours before the onset of their symptoms. Those contacts are then called by tracers and told they must also isolate at home or monitor for symptoms. It’s time-consuming gumshoe work: in normal circumstances, it takes eight to ten people working for about twelve hours to complete one case, says Richelle Schindler of Alberta Health Services. (When robust physical distancing measures are in place, she says, one investigator can wrap up an average case in about nine hours.)

Unsurprisingly, many people in the tech industry are eager to disrupt this labour-intensive work and have offered new ways to expedite the process. Digital contact-tracing harnesses Bluetooth-equipped smartphones to detect when two people have been in close proximity. Once a person tests positive for sars-CoV-2, they report their diagnosis to a purpose-built app, which notifies close contacts through that same app, prompting them to isolate or get tested. In April, Google and Apple announced a rare collaboration to produce an opt-in contact-tracing platform that would work on their respective Android and iOS phones—without tracking user locations or necessitating any identifying data.

Other countries are test-driving their own approaches to digital tracing. When someone in South Korea tests positive, for example, health authorities issue regional text messages, alerting residents to a website that omits the person’s name but does include details about their age range, gender, and the various places they’ve recently visited. New Zealand is reportedly considering passing out “Covid Cards,” a system that swaps a smartphone for something the size of a credit card, with Bluetooth capability and a battery life of roughly a year. In Quebec, deep-learning pioneer Yoshua Bengio proposed an app that would calculate your covid-19 risk score depending on where you’ve been and who you’ve encountered.

Some provinces, including Alberta, New Brunswick, and Newfoundland and Labrador, have launched or are close to launching their own voluntary contact-tracing apps. But these digital tools raise serious questions about abuses of power, says Sean McDonald, a senior fellow at the Centre for International Governance Innovation. “Often, in the tech community, there’s the idea that responsibility ends at the product, not at the impact. I think people are asking themselves, ‘Did I produce good location data?’ and not, ‘Am I shouting fire in a movie theatre with no exits?’” Can it be possible for these apps to link back to an individual’s identity? Will they be marshalled for discrimination? Is there a risk of what the American Civil Liberties Union called “surveillance creep” once the pandemic has passed? “If you’re inventing it now,” McDonald says, “chances are it’s not ready.”

Even setting those questions aside, contact-tracing apps run the very real risk of simply being ineffective. Unlike human contact tracers, apps don’t seem to be able to distinguish between two strangers who are in so-called contact as they pass each other in a park and two family members living in the same house. They also don’t appear to distinguish between open and closed space: since Bluetooth signals can sometimes pass through walls, the apps will not know if people have been separated by car doors or are in entirely different apartments. In Israel, an app used by the security agency Shin Bet sent a woman into quarantine after it flagged contact with her infected partner. She had been waving at him from outside the building.

To achieve what they promise, contact-tracing apps also need considerable uptake among prospective users: researchers at Stanford and the University of Waterloo estimated that 50 to 70 percent of a population would have to sign up. That’s a problem when half the world doesn’t own a smartphone. In countries where their use is pervasive, researchers at the University of Oxford found that 80 percent of smartphone owners would need to install the app before it could be effective.

Technology isn’t anathema to human contact tracers: they draw on texts, location history, digital calendars, and transaction records to find the people who’ve entered an infected person’s orbit. “But technology doesn’t replace that clinical judgment of how close is too close, how long did people actually spend together, and what constitutes the onset of a symptom,” says Schindler, who, in the first month of the pandemic, hired roughly 400 medical students, residents, and recently retired health care providers to help Alberta Health Services with this work.

Human tracers don’t need to capture every contact an infected person has had in order to be effective, she adds. The government of Ontario, for example, says it must reach about 90 percent of new covid-19 contacts within twenty-four hours as part of its plan to reopen the economy. It’s hard to pin an exact number on how many contact tracers we need: California, which has a similar population to Canada, plans to hire and train 10,000 tracers to do the job, though much depends on how well we’ve observed physical-distancing measures. But, as those measures relax and as more asymptomatic people are able to be tested and diagnosed, contact tracers will continue to be essential to containing community spread. The federal government launched a national recruitment campaign in early April to help with case tracking. By the time applications closed a few weeks later, the cbc reported, nearly 58,000 people had offered to take part.

As ron klain, former president Barack Obama’s Ebola czar, has said, the virus is more patient than people are. Places like Hong Kong, Singapore, and Taiwan, heralded in March as models for containment, had to contend a month later with a new wave of cases, leading to stricter physical-distancing measures and additional shutdowns. The mass quarantine in Wuhan, China, where the novel coronavirus was first detected, was only relaxed after seventy-six days—and even then, the more modest lockdown that followed looked a lot like Canada’s initial approach, with sweeping residential restrictions, school closures, and restaurants open for deliveries only.

The process of reopening will, by necessity, continue to be painstaking and slow. The challenge for policy makers and politicians is that, because we shut a bunch of things down at once, it’s hard to know which measures have worked best and which ones can be walked back. “We’re flying blind right now,” says Fabian Lange, a professor of economics at McGill University. “There are lots and lots of variables that we have very little idea about, both epidemiologically and in terms of the economy.”

Each province has undertaken its own risk-benefit approach to relaxing some of the physical-distancing measures in a targeted way. “It seems like younger individuals are not getting into as much medical trouble, even if they’ve been exposed,” says epidemiologist John McLaughlin, who retired last year as the chief science officer for Public Health Ontario. That notion informed Quebec premier François Legault’s push to reopen smaller daycares and elementary schools in the middle of May, even over the objections of parents. New Brunswick, which had called off its school year completely more than a month earlier, allowed two households to form a shared bubble, permitting some social interaction while minimizing the risk of spreading the disease. Manitoba kept its schools closed but let hair salons, restaurant patios, and museums reopen at reduced capacity, while Ontario sent seasonal businesses like garden centres to the front of the line. Ontario’s road map for recovery also said sectors could reopen if they modified operations to meet public health requirements. Though, as University of British Columbia Sauder School of Business professor Harish Krishnan notes, if everyone pegs Plexiglass sneeze guards as a great way to separate customers at a restaurant, “we’re going to see a bottleneck of Plexiglass in the global supply chain emerge very quickly.”

Every change made to the interventions requires being incredibly responsive to the first sign of danger: greater numbers of still-susceptible people out in the world result in rising covid-19 cases. When Quebec announced it would reopen schools, the province’s director of public health, Horacio Arruda, promised to change course if hospitals became too crowded or too many people died. Ontario likewise insists a surge in cases will result in tightened measures, as do Alberta, Manitoba, and Saskatchewan. Upshur compares easing restrictions to sparks shooting off a campfire: “As soon as one of those sparks gets loose onto a pine needle lying around, it’s tinder for another fire.” Ease too many measures too quickly and the tinder ignites—and we’re back to contending with an out-of-control pandemic.

That’s why epidemiologist Ashleigh Tuite and her colleagues at the Dalla Lana School of Public Health proposed a strategy they call dynamic physical distancing, which turns the potential for freshly tightened measures into part of the actual long-term plan. “You look at what’s happening in your icus and, based on their capacity, you then dial your interventions up and down,” she explains. They chose icu capacity because it is, right now, a barometer Canada has a good sense of; with more consistent and comprehensive testing, that barometer could instead be the virus’s reproduction number, which is the average number of new cases one infected person generates. Either way, the approach is the same: as long as the virus can be managed, distancing measures can be eased, but the moment that new cases begin to reapproach that threshold, stricter interventions are turned back on. “Cases go up a bit, we react, they go down, up and down,” Tuite says. It’s another kind of shape we might soon get to know well. Instead of the curve—one line that rises, flattens, and eventually declines—this model looks more like an ocean wave, rising and falling as we toggle between bouts of distancing that respond to new outbreaks.

In Tuite’s models, flattening the curve so it stays at a level that does not overwhelm our health care system requires at least a year of physical-distancing vigilance. “I definitely think there is going to be fatigue in terms of twelve to eighteen months of complete shutdown,” she says. On the other hand, dynamic physical distancing—call it riding the wave—“allows us to come up for air once in a while, and that’s important.” A week after Tuite’s study was published in the Canadian Medical Association Journal, a Harvard study in Science magazine proposed similarly intermittent phases of distancing directed by the prevalence of outbreaks and the capacity of health care systems in their respective communities. The idea is now guiding our national approach: in a joint statement with the premiers, Justin Trudeau said that public health measures should be flexible and proportionate, relaxed and possibly reintroduced based on the level of threat. That could also help ease apprehensive citizens back into the world, since an Angus Reid poll found that only 11 percent of Canadians say they’d resume their former routines as soon as restrictions lifted. Everyone else would wait and see.

Okay, then: How long would we need to ride this wave? “We ran this model for two years under the hopefully-not-overly-optimistic idea that, in two years, we’ll have a vaccine,” Tuite says. The Harvard researchers reached that same conclusion: to avoid exceeding critical-care capacity, intermittent physical-distancing measures would be required until 2022.

Upshur worries that developing a safe, effective vaccine in eighteen or twenty-four months “would be breaking land-speed records.” McLaughlin is more optimistic. “Compared to any other public health challenge in the past, the vaccine will come fairly soon, I believe,” he says. “It’s fascinating to see what happens when nations and disciplines of science work together.” In late April, the World Health Organization convened heads of government, global health experts, and philanthropists in a pledge to work together on the development and production of tests, treatments, and a vaccine; in early May, Trudeau and other world leaders promised to raise nearly $12 billion for the cause. “We could get clinical trials starting in six months, maybe sooner,” McLaughlin says, “and, if there’s evidence of safety and efficacy within a year, that’s fantastic. That is a tremendous accomplishment.”

But we need to accept that we aren’t anywhere near the end of this pandemic. Until the vaccine arrives, and unless sars-CoV-2 mutates into a more benign virus, we must make these small, careful adjustments as we emerge tentatively from our lockdown and settle into the next phase. And that reality brings with it the distinct possibility that we’ll engage in some version of physical distancing again, and again, then again. “The virus doesn’t care about our dreams and aspirations,” Upshur says. “You can’t reason with a virus to go away.” So, for now—and maybe for next year too—we should take our cues from the virus itself. We’re going to have to be patient.

Correction May 26, 2020: An earlier version of this story stated that an antibody test with 100 percent sensitivity means that every positive is a true positive. In fact, the test could provide a false positive, although it will not provide a false negative. The Walrus regrets the error.

Danielle Groen
Danielle Groen (@daniellegroen) is a Toronto-based writer who won the 2018 Allan Slaight Prize for Journalism.
Jeremy Fokkens
Jeremy Fokkens (jeremyfokkens.com) is the creator of a Canada-wide photography project called "Back to the Land."
Mark Rowe
Mark Rowe is an art director. His portfolio includes projects for Earls, Sunkist, Sprint, Bow Valley College, Best Buy, and Big Rock Brewery.

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