text: When Amy Greer received the ProMED warning at the end of 2019, her mind blinked back a decade to the 2009 H1N1 influenza pandemic. At the time of the virus' second wave, she had worked for the federal public health agency, supporting the country's pandemic preparedness and response activities. She remembered building mathematical models, estimating and re-estimating the potential spread of what was commonly called swine flu, after its similarity to influenza viruses found in pigs in North America and Eurasia. Like the strange new coronavirus, the then-new influenza had a unique combination of genes that had never been seen in either humans or animals. The first worldwide case was reported in Mexico on March 18, 2009, and it would go on to kill more than four hundred Canadians. Greer, now a professor at the University of Guelph and a Canada Research Chair in Population Disease Modelling, called a few colleagues whom she worked with on H1N1. She wanted to know if they'd also been following the news out of Wuhan.
  
  "I don't know if I'm being paranoid or not," she told them, laughing, just a little, at the absurdity of what she was about to say. "This might be a complete waste of time." Hesitation. "But maybe we should dust off our pandemic models." Her colleagues agreed, and together they started building the necessary code, hoping they wouldn't have to use it. By late February, Greer started going through her pantry, taking stock. Her husband was startled. "He said, 'Geez, normally you're very laid back,'" she recalled. "'If you're telling me we need a quarantine stockpile, then I'm starting to get worried.' " So was Greer. They tried to think of everything they might need. She quizzed herself: Do we have batteries for the thermometer? Do we have an extra bottle of children's Advil? If everything shuts down, are we ready? At work, she asked different questions, formulating distinct scenarios based on the dynamics of the emerging pathogen and then projecting that knowledge forward in time: If we did nothing to mitigate transmission, what would happen a month from now, two, three? What if we retreated, actually did shut down everything, distanced from each other? What if we all wore masks? What would be necessary to slow down transmission?
  
  Without strict intervention, many possible outcomes showed the same thing: collapse. Epidemiologists and mathematical modellers were still learning about the biology of the virus, but they did know it appeared to be highly transmissible. In scant weeks, the virus had undulated across the globe, spreading through Italy, Iran, and Brazil. It had skulked aboard a cruise ship anchored on a Japanese shoreline, infecting more than six hundred people—at the time, the largest outbreak outside China. Models from different countries, even using slightly different methods, consistently estimated that 60 to 70 per cent of their populations could become infected if the virus were to spread unchecked, without interception by public health. The numbers felt staggering, unfathomable. The air buzzed with the possibility of mass death. It buzzed with denial. Even Greer and her colleagues couldn't say with certainty what would happen. The new coronavirus was behaving in puzzling ways. Most viruses wreak havoc on the very old and the very young. During the 1918 Spanish flu pandemic, mortality rates were particularly high for children under age five. Children also suffered more during swine flu. But SARS-CoV-2 barely seemed to infect children at all. Many wondered if kids were actually faring better or if they just hadn't had the chance to become infected yet.
  
  As new information trickled through to her via open access research networks, Greer adjusted and updated her models, emailing the findings to her network of government contacts and public health officials. The virus may have been a series of question marks punctuated by even bigger question marks, but she did know that, to slow transmission, people needed to significantly change their day-to-day behaviour. She knew it would be a hard sell. In mid-March, many parts of the country still had zero cases. The virus felt terrifying, but also mythical, a fire-breathing dragon, a Marvel villain, something from over there. She worried politicians would be willing to wait until there were more cases, and then it would be too late to put on the brakes. Hospital intensive care units would be overwhelmed. Ventilator capacities would buckle. She was surprised, and relieved, when immediate, aggressive stay-at-home orders were issued. She also knew that, despite hopes at the time, three weeks wouldn't be enough. So, when the National Post asked her what it would take to stop thousands of deaths, she answered honestly.
  
  For centuries, the idea of social distancing and mass lockdowns have figured strongly in public health responses to disease outbreak. During the 1918 Spanish flu, which would be deeply mined for lessons in pandemic management in the months ahead, cities all over the world limited public gatherings and adjusted business practices. Some did so drastically; others, less so. New York City merely staggered its business hours, for instance, with the aim of reducing crowds. It also educated city-dwellers on the dangers of coughing and spitting in public. Other cities shut down everything, including schools, libraries, movie theatres, stadiums, and any other places where people gathered in mass numbers. San Francisco and San Diego required anybody who went out in public to wear a gauze mask. But, just like with COVID-19, timing mattered. Cities that waited weeks to implement measures—even those with the strictest rules—suffered high mortality rates. (Philadelphia had one of the highest in the U.S.; it knowingly held a parade after the virus had started infecting the city.) Other places that acted immediately, such as St. Louis, fared better. So too did cities that refused to lift restrictions as the pandemic peaked. Then, just as now, the dissemination of information also mattered. Some media downplayed the pandemic, encouraging a false sense of safety. And, on top of that, wrote Joshua Loomis in Epidemics: The Impact of Germs and Their Power over Humanity, politicians worldwide couldn't seem to agree on anything: "This produced unnecessary delays and created confusion in populations who often were getting mixed messages." Sound familiar?
  
  One hundred years later, similar sacrifices would be just as difficult to sell to the public. On March 21, the National Post printed an article quoting Greer, who said thirty-two weeks of strict public health measures were needed to prevent Canada, and its healthcare system, from becoming overwhelmed. "The challenge in all of this is it's unprecedented," she said. "We're asking people to do something that is really challenging and we're going to be asking them to do it for a very long time." Many people read this as if Greer, personally, were ordering them into a long lockdown. Within hours, she began to get a "boatload" of hate emails. Even family and friends began to reach out, enraged, telling her the virus was a conspiracy, the measures overkill. Strangers told her she was ruining their child's high school graduation, that she'd ended prom, bungled family vacations. Greer was perplexed. In her mind, the message was simple: We need to think about how we're going to keep people safe, or else. In a way, the hateful emails weren't entirely wrong. For people to live and for our healthcare system to survive, graduations and proms would need to be cancelled. Still, while the unexpected onslaught exhausted her, Greer didn't feel bad about sharing data that supported long periods of public health measures, such as physical distancing and mask-wearing. As the country retreated inside, she thought, It's better than killing your grandparents.