As countries across the Asia-Pacific region struggle with resurgences of the coronavirus, one data point is steering government responses: the share of cases with no clear indication of how infection occurred.
These patients cannot be linked to other confirmed infections or existing outbreaks by virus responders, indicating hidden chains of transmission. A growing proportion of such cases in a city’s resurgence pushes governments, like in Australia and Hong Kong, to take broad and blunt action, returning entire cities to lockdown-like conditions.
"You can hardly contain the outbreak because you have no idea where they will come out next,” said Yang Gonghuan, former deputy director general of China’s Center for Disease Control and Prevention. "When there’s more cases where the origins are unknown, it adds to the difficulty for containment.”