Most people who catch Covid-19—the disease caused by the novel coronavirus—start showing symptoms roughly five days after infection, disease analysts at Johns Hopkins University said on Monday, in the largest such study of known cases world-wide.

Their findings firm up estimates of the virus’s incubation period before signs of fever, coughing and respiratory distress appear, offering support for current public-health control measures that recommend a 14-day monitoring and quarantine period for people who have been exposed...