How much is coronavirus spreading under the radar?
Just how much has the coronavirus spread? More than 137,000 people in 117 countries and regions have been confirmed as having COVID-19. And earlier this week, the World Health Organization (WHO) described the outbreak as a pandemic. But testing isn’t available to everyone, so the numbers don’t accurately reflect the extent of transmission in communities around the world.
Based on conversations with three leaders in public health — at the WHO, the US Centers for Disease Control and Prevention (CDC) and at one of one of the largest research charities in the world — Nature explains how officials and researchers are attempting to estimate the size of individual outbreaks based on incomplete data.
Has the coronavirus that causes COVID-19 been spreading undetected in some populations?
“Yes, unequivocally,” says Jeremy Farrar, an infectious disease specialist and director of the research charity Wellcome, in London. A telltale sign of covert transmission in communities is finding a few confirmed but unrelated cases, with no recent history of international travel. That means these cases are connected through a hidden web of infections. The ideal way to know how many people in a community have had coronavirus infections , Farrar says, is to collect blood samples from people in every age group, looking for antibodies against the coronavirus, which show that someone has previously been infected. Data from such serology studies, as they are called, can then be used to accurately determine rates of fatality and transmission. But such studies take time. “We need to make policy decisions and clinical decisions now,” Farrar says. “You can’t say, ‘Let’s wait a month until we have the data.’”