Marina Pollán of the Carlos III Health Institute in Madrid, who led Spain's antibody survey, says Africa's youthfulness may protect it. Spain's median age is 45; in Kenya and Malawi, it's 20 and 18, respectively. Young people around the world are far less likely to get severely ill or die from the virus. And the population in Kenya's cities, where the pandemic first took hold, skews even younger than the country as a whole, says Thumbi Mwangi, an epidemiologist at the University of Nairobi. The number of severe and fatal cases "may go higher when the disease has moved to the rural areas where we have populations with advanced age," he says.