Background: Pre-symptomatic transmission can be a key determinant of the effectiveness of containment and mitigation strategies for infectious diseases, particularly if interventions rely on syndromic case finding. For COVID-19, infections in the absence of apparent symptoms have been reported frequently alongside circumstantial evidence for asymptomatic or pre-symptomatic transmission. We estimated the potential contribution of pre-symptomatic cases to COVID-19 transmission.
Methods: Using the probability for symptom onset on a given day inferred from the incubation period, we attributed the serial interval reported from Shenzen, China, into likely pre-symptomatic and symptomatic transmission. We used the serial interval derived for cases isolated more than 6 days after symptom onset as the no active case finding scenario and the unrestricted serial interval as the active case finding scenario. We reported the estimate assuming no correlation between the incubation period and the serial interval alongside a range indicating alternative assumptions of positive and negative correlation.
Results: We estimated that 23% (range accounting for correlation: 12 - 28%) of transmissions in Shenzen may have originated from pre-symptomatic infections. Through accelerated case isolation following symptom onset, this percentage increased to 46% (21 - 46%), implying that about 35% of secondary infections among symptomatic cases have been prevented. These results were robust to using reported incubation periods and serial intervals from other settings.
Conclusions: Pre-symptomatic transmission may be essential to consider for containment and mitigation strategies for COVID-19.
Bibliographical noteFunding Information:This work was supported by the Wellcome Trust through a Wellcome Senior Research Fellowship to Sebastian Funk  and a Sir Henry Dale Wellcome Trust Fellowship to Stefan Flasche . Yang Liu was partially funded by the Bill & Melinda Gates Foundation [INV-003174] and the National Institute for Health Research (NIHR) [16/137/109] using UK aid from the UK
Government to support global health research. The views expressed in this publication are those of the author(s) and not necessarily those of the NHS, the NIHR or the UK Department of Health and Social Care. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Open Access: This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Publisher Copyright: © 2020 Liu Y et al.
Citation: : Liu Y, Centre for Mathematical Modelling of Infectious Diseases nCoV Working Group, Funk S and Flasche S. The contribution of pre-symptomatic infection to the transmission dynamics of COVID-2019 [version 1; peer review: 3 approved]
Wellcome Open Research 2020, 5:58
- Incubation period
- Pre-symptomatic transmission
- Serial interval