Nearly every morning, at eleven o’clock, Allison Arwady takes a seat at a round table in front of a video camera, with a laptop and a set of charts before her, and answers questions about COVID-19 from worried Chicago residents. Arwady, the city’s commissioner of public health, displays graphs that show the number of positive cases, and explains the demographics of the city’s death toll. A primary-care doctor who previously worked for the Centers for Disease Control and Prevention, staffing an Ebola outbreak in Liberia, she offers practical advice in upbeat and accessible language. If you touch an elevator button or a doorknob while you are out, wash your hands. If you go to the store, make a list, move efficiently, and don’t touch your face. Germs do not jump from grocery-cart handles into your nose or mouth, she likes to say.

Arwady, who is forty-three, and oversees a staff of five hundred, spends her days interpreting streams of data about the unpredictable path of the contagion. So far, it has killed more than five hundred people in Chicago. As she scrambled last month to prepare for a wave of COVID-19 cases, Arwady saw shortages and dysfunction that reminded her of Liberia in 2014. Then and now, she said, she had a sense of “I just need somebody to listen.” She had a dream the other night that she was solving all sorts of problems, only to wake up and realize that none of it had been done.

As Mayor Lori Lightfoot’s top public-health adviser, Arwady will be a central figure in the perilous next phase of Chicago’s response to the virus, when Lightfoot and Governor J. B. Pritzker decide when to lift restrictions on the city—and how to monitor and block the spread of the virus as infections inevitably continue. Political and business leaders across the country are confronting these questions, with the added pressure of President Trump’s hectoring demands for a swift economic rebirth. Pretty much everyone promises to be guided by data and science. And yet, as Arwady and her colleagues in medical research and public health point out, the data are riddled with imperfections and the science is racing to keep up. Four months into the pandemic, knowledge about the virus, how deeply it has spread, and what can stop it remains frustratingly thin. As Harlan Krumholz, a cardiologist and researcher at the Yale School of Medicine, put it to me, “We’re so damned ignorant about this thing.”

In practical terms, the United States is facing a prolonged period of trial and error as cities and states navigate the long stretch before a vaccine becomes available, likely sometime in 2021. Different states and communities will open at different speeds and will face varying degrees of risk from a pathogen that is proving cruelest to elderly and African-American residents. There is nothing to indicate that COVID-19 is any less deadly simply because several weeks have passed since social distancing began. Chicago’s opening, when it comes, will be gradual, and answers won’t come quickly, especially if the gaps in testing remain unfilled. Arwady said, “You have to be able to make sure you’ve got good, real-time data. If you make some change, you’ve got to wait a couple of weeks to really see how that works.” At a press conference last week, Lightfoot similarly sought to dampen expectations: “What we can’t do, as other places across the globe have done, is come out of these stay-at-home measures too soon, following some gains, only to have cases surge all over again.”

Chicago was one of the first U.S. cities to identify COVID-19 cases, and among the first to implement widespread closures. On March 13th, Pritzker announced the closure of all Illinois schools. On March 20th, four days after Chicago’s first death, he issued a stay-at-home order. Since then, Lightfoot has shut down access to public areas along Lake Michigan and ordered liquor stores to close at 9 P.M., to prevent customers from congregating. Today, car traffic is sparse in the city and suburbs. Passenger jets, typically lined up in the night sky, headed to O’Hare International Airport like orderly fireflies, are mostly gone. Many pedestrians are wearing masks, but the practice is far from universal. At the Beth Eden Baptist Church in the working-class Roseland neighborhood, on the far South Side, where Barack Obama was a community organizer in the mid-eighties, an electric sign announces that in-person services have been suspended, though the prayer line is open. “Stay safe and follow the guidelines set by the CDC,” the sign flashes. “Wash hands for at least 20 seconds.” With more than forty-six hundred people hospitalized in Illinois due to COVID-19 at last count, including more than twelve hundred in intensive care, some hospitals are struggling more than others. The president of Roseland Community Hospital, down the street, told the Chicago Tribune, “We are outgunned, outmanned, underfunded, and no one is coming to help us.”

There are signs that, with severe social-distancing measures, Chicago’s outbreak is slowing. COVID-19 cases are now doubling every twelve days, compared with every two or three days in mid-March. Still, as summer beckons and, with it, baseball season and music festivals, including Lollapalooza, Pritzker urged organizers of large events to “think carefully about canceling.” In order to consider any reopening, he said, Illinois must conduct at least ten thousand coronavirus tests a day, to know who is infected with the virus and where it is spreading. “Obviously, we want more than that,” Ngozi Ezike, the director of the Illinois Department of Public Health, told me. Her laboratories are working extra shifts to conduct tests, while also delivering equipment to hospitals and universities. Still, the state has been falling well short of Pritzker’s target number. Illinois has machines available to examine large numbers of specimens, he said this week, but “we don’t have the supplies to run those tests.”

From the beginning, the federal government has been slow to develop or support testing. An early test created by the Centers for Disease Control and Prevention was flawed, leading to unreliable results and weeks of delay. Since then, labs nationwide have suffered from a lack of supplies needed to conduct tests, including nasal swabs, reagent, and the personal protective equipment that technicians need when gathering specimens. Trump has adamantly avoided developing a national testing strategy while instructing governors, by tweet, to perfect their testing programs: “Be ready, big things are happening. No excuses!” On March 6th, Trump falsely declared, “Anybody that wants a test can get a test,” a claim that remains untrue six weeks later. On March 10th, Vice-President Mike Pence promised during a White House briefing that four million tests would be available within a week. The total number of tests conducted since the pandemic began is only slightly more than four million, according to the White House’s own count. On Friday, the American Association for Clinical Chemistry said that the federal government is the only institution that can solve the critical supply shortages for tests, which are required under the White House’s own guidelines for reopening the country. Lightfoot, who has spoken publicly about her frustration with the scattershot White House response, believes that Chicago is “still not testing nearly enough people” and says that she has raised the issue with Pence.