Lessons learnt from 288 COVID-19 international cases: importations over time, effect of interventions, underdetection of imported cases

Pinotti, Francesco; Di Domenico, Laura; Ortega, Ernesto; Mancastroppa, Marco; Pullano, Giulia; Valdano, Eugenio; Boelle, Pierre-Yves; Poletto, Chiara; Colizza, Vittoria

288 cases have been confirmed out of China from January 3 to February 13, 2020. We collected and synthesized all available information on these cases from official sources and media. We analyzed importations that were successfully isolated and those leading to onward transmission. We modeled their number over time, in relation to the origin of travel (Hubei province, other Chinese provinces, other countries) and interventions. We characterized importations timeline to assess the rapidity of isolation, and epidemiologically linked clusters to estimate the rate of detection. We found a rapid exponential growth of importations from Hubei, combined with a slower growth from the other areas. We predicted a rebound of importations from South East Asia in the upcoming weeks. Time from travel to detection has considerably decreased since the first importation, however 6 cases out of 10 were estimated to go undetected. Countries outside China should be prepared for the possible emergence of several undetected clusters of chains of local transmissions.