Virus World

How many people have really been infected by the coronavirus? In one German town a preliminary answer is in: about 14%. The municipality of Gangelt, near the border with the Netherlands, was hard hit by covid-19 after a February carnival celebration drew thousands to the town, turning it into an accidental petri dish. Now, after searching blood from 500 residents for antibodies to the virus, scientists at a nearby university say they have determined that one in seven have been infected and are therefore “immune.” Some of those people would have had no symptoms at all. Their brief report (PDF), posted online in German, has big implications for how soon that town, and the rest of the world, can come out from lockdown. 

 

“To me it looks like we don’t yet have a large fraction of the population exposed,” says Nicholas Christakis, a doctor and social science researcher at Yale University. “They had carnivals and festivals, but only 14% are positive. That means there is a lot more to go even in a hard-hit part of Germany.” Here's why the true infection rate in a region matters: the bigger it is, the less pain still lies ahead. Eventually, when enough people are immune—maybe half to three-quarters of us—the virus won’t be able to spread further, a concept called herd immunity. But the German town isn’t close to that threshold yet, and to Christakis the preliminary figure is “unfortunate” because it means the virus still has more damage to do.

 

The German report is among the first to survey a population for evidence of prior infection, data that scientists need to determine how far the pandemic has spread, what the real death rate is, and how many people show no symptoms at all. “It’s very preliminary, but it’s the kind of study we desperately need,” says Christakis, who believes the US should test as many as 200,000 people, from big cities like New York to small towns in the Midwest. “This is crucial to quantify a host of basic parameters.”