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Transmission of corona virus disease 2019 during the incubation period may lead to a quarantine loophole

By Wei Xia, Jiaqiang Liao, Chunhui Li, Yuanyuan Li, Xi Qian, Xiaojie Sun, Hongbo Xu, Gaga Mahai, Xin Zhao, Lisha Shi, Juan Liu, Ling Yu, Meng Wang, Qianqian Wang, Asmagvl Namat, Ying Li, Jingyu Qu, Qi Liu, Xiaofang Lin, Shuting Cao, Shu Huan, Jiying Xiao, Fengyu Ruan, Hanjin Wang, Qing Xu, Xingjuan Ding, Xingjie Fang, Feng Qiu, Jiaolong Ma, Yu Zhang, Aizhen Wang, Yuling Xing, Shunqing Xu

Posted 08 Mar 2020
medRxiv DOI: 10.1101/2020.03.06.20031955

BackgroundThe ongoing outbreak of novel corona virus disease 2019 (COVID-19) in Wuhan, China, is arousing international concern. This study evaluated whether and when the infected but asymptomatic cases during the incubation period could infect others. MethodsWe collected data on demographic characteristics, exposure history, and symptom onset day of the confirmed cases, which had been announced by the Chinese local authorities. We evaluated the potential of transmission during the incubation period in 50 infection clusters, including 124 cases. All the secondary cases had a history of contact with their first-generation cases prior to symptom onset. ResultsThe estimated mean incubation period for COVID-19 was 4.9 days (95% confidence interval [CI], 4.4 to 5.4) days, ranging from 0.8 to 11.1 days (2.5th to 97.5th percentile). The observed mean and standard deviation (SD) of serial interval was 4.1{+/-}3.3 days, with the 2.5th and 97.5th percentiles at -1 and 13 days. The infectious curve showed that in 73.0% of the secondary cases, their date of getting infected was before symptom onset of the first-generation cases, particularly in the last three days of the incubation period. ConclusionsThe results indicated the transmission of COVID-9 occurs among close contacts during the incubation period, which may lead to a quarantine loophole. Strong and effective countermeasures should be implemented to prevent or mitigate asymptomatic transmission during the incubation period in populations at high risk.

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