Temporal dynamics in viral shedding and transmissibility of COVID-19

Xi He; Eric HY Lau; Peng Wu; Xilong Deng; Jian Wang; Xinxin Hao; Yiu Chung Lau; Jessica Y Wong; Yujuan Guan; Xinghua Tan; Xiaoneng Mo; Yanqing Chen; Baolin Liao; Weilie Chen; Fengyu Hu; Qing Zhang; Mingqiu Zhong; Yanrong Wu; Lingzhai Zhao; Fuchun Zhang; Benjamin J Cowling; Fang Li; Gabriel M Leung

is the (which was not peer-reviewed) The copyright holder for this preprint . https://doi.org/10.1101/2020.03. 15.20036707 doi: medRxiv preprint patient subgroups which demonstrated a different viral shedding pattern and our results is likely applicable to COVID-19 patients generally. Whereas a recent study from Wuhan reported that virus was detected for a median of 20 days (up to 37 days amongst survivors) after symptom onset, 11 infectiousness may decline significantly after 10 days. 12 Together this supports our findings that the infectiousness profile may more closely resemble that of influenza than of SARS (Figure 1a ), although we did not have data on viral shedding before symptom onset for COVID-19. 9, 13 Our results are also supported by reports on asymptomatic and pre-symptomatic transmission. 14, 15 For a reproductive number of 2.5, 2 contact tracing and isolation alone are less likely to be successful if more than 30% of transmission occurred before symptom onset, unless >90% of the contacts can be traced. 16 Such high ascertainment is more likely achievable if the definition of contacts covered 2-3 days prior to symptom onset of the index case, as is being done in Hong Kong since 22 February and in mainland China since 21 February. Even when control strategy is shifting away from containment to mitigation as the pandemic unfolds, contact tracing would still be an important measure, such as when there are superspreading events that may occur in frail and high-risk groups such as nursing homes or hospitals. Preliminary indications of pre-symptomatic infectivity of COVID-19 cases has already prompted enhanced pre-emptive preventive measures in the nosocomial setting and in the community, especially for high risk groups such as older adults and those with pre-existing medical conditions. With a substantial proportion of pre-symptomatic transmission, measures such as enhanced personal hygiene among the general population . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity.