On a bright morning in May, Isabel Klugherz, a medical student at Ludwig-Maximilians University, in Munich, arrived at the geographical center of the city’s Milbertshofen district. Over the previous month, as Munich’s streets emptied under lockdown orders, an exception had been granted for roving medical students in mint-green scrubs and face masks. The university’s department for infectious diseases was screening for the seroprevalence of SARS-CoV-2—antibody testing—by sending police-escorted teams on the winding pattern of a predetermined algorithm, otherwise known as a random walk. Start in the center of an electoral district, continue past a few houses, cross to the other side of the street, select the third house, and knock. In the past month, Klugherz had knocked on nearly a thousand doors, and residents had been overwhelmingly enthusiastic about participating; one man had pronounced it more important than his Sunday celebration of the Holy Mass. That morning, the algorithm led Klugherz into a quiet road of whitewashed modernist buildings. The day before, she had texted a friend who lived nearby to let him know that she would be in the area. Now, unexpectedly, the algorithm led her to his door. She rang the bell. When her friend answered, and found Klugherz standing outside, he was still in his pajamas.
In late March, the government of the state of Bavaria, which includes Munich, was trying to decide how to respond to what appeared to be an accelerating community spread of COVID-19. Michael Hoelscher, the director of the Department of Infectious Diseases and Tropical Medicine at L.M.U., was involved in official debates about whether to impose a citywide lockdown. That, to him, was a foregone conclusion. Considering the disease’s rate of transmission, under the most extreme scenarios, it could take about two and a half years to reach herd immunity in Germany. “Not an option,” Hoelscher said. What was less clear was how the city could effectively track the disease’s spread. Because so many cases of COVID-19 appeared asymptomatic, as Hoelscher had first noted in a paper published in January, diagnostic testing alone would only provide a partial measurement. “So I said, ‘O.K., we need something,’ he told me. The only way to get an accurate measurement of the epidemic, he reasoned, was to implement wide-scale antibody testing. Within six hours, just before the lockdown was announced, on March 21st, he received a million euros from the government.
Hoelscher is tall, with a wave of blond hair that he keeps brushed back cleanly from his face; on the day we met, he was dressed in slim-fitting jeans and a normcore sweater layered over a blue Oxford shirt. Like many infectious-disease researchers of his generation, Hoelscher began his career working on H.I.V. and AIDS. In the early two-thousands, he ran a study on sex workers and bar workers in Tanzania to learn whether it was possible to be infected with H.I.V. more than once. (Deborah Birx, the coördinator of the White House Coronavirus Task Force, was one of his collaborators.) “Take H.I.V.,” Hoelscher said. “You have the disease, you produce an immune response, and that immune response, No. 1, is not able to kill the virus itself. But it can also not protect you from getting a second H.I.V. infection.” The H.I.V. virus, his team discovered, was able to “hide” itself in the immune response, transcribing its genome into the cells. “So that’s an example where the antibody doesn’t help against it,” he said. “In history so far, we only have been able to produce or manufacture a vaccine if the natural immune response would be able to prevent a secondary infection.”
SARS-CoV-2 is obviously different. But it is also exhibiting unusual features. “It can affect multiple organs,” Hoelscher said. “Not only the lower respiratory tract. It can replicate in the upper respiratory tract, it can most likely replicate in different organs.” The course of the disease, the time that it remains in the body, is long, and in some cases, his team found, the immune response does not develop until nearly two months after an infection. “Absolutely surprising or frightening,” Hoelscher said, “is that there might be really some reason to believe that you cannot eliminate it from your body.”
Not far from Hoelscher’s office, L.M.U. had set up a testing tent near the poplar trees of Leopoldstrasse, an imperious boulevard that runs through town. Test subjects who preferred to have their blood drawn outside of their home could come here instead. Outside the tent’s entrance, I met Michael Pritsch, a young infectious-disease doctor who works in Hoelscher’s lab. Pritsch is helping to run the study, but he had come to the tent to get tested himself. In late April, medical students he’d trained had followed the algorithm and ended up at his front door. “My home was my castle,” Pritsch told me. “When I came home after sixteen hours of work, I had my five minutes of free time.” And then they rang his bell. “Even at home, I’m not without this coronavirus thing,” he said. Two students in scrubs and masks welcomed him into the tent and offered him a new mask. He signed a consent form, which he’d helped write, and then pushed up his sleeve as one of the students knotted a rubber tourniquet around his upper arm. Pritsch suggested, wryly, that he would probably check his own data. (“Don’t write that!” he said.)
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