Data from several countries — notably Iceland — suggest that children are less likely to give the virus to their parents or other adults than to catch it from them. Other research counters that children may be just as contagious as adults.

Perhaps the most controversial such study was done by a team around Christian Drosten, a virologist here in Berlin who’s become a national celebrity since the outbreak. They published a paper showing that the viral load in children is similar to that in adults. Drosten concluded that children are infectious enough to warrant keeping schools closed.

But other scientists, including statisticians, have questioned the Drosten team’s math. Drosten now plans to update his study with more detailed data. As a sign of just how charged the controversy has become, this week he received a package containing a vial filled with an apparently dangerous liquid and the instruction, “drink this – it’ll make you immune.” Meanwhile, several German pediatric associations have concluded that children are indeed significantly less contagious, and that schools should be opened.