The contribution of asymptomatic SARS-CoV-2 infections to transmission on the Diamond Princess cruise ship
- London School of Hygiene and Tropical Medicine, United Kingdom
Abstract
A key unknown for SARS-CoV-2 is how asymptomatic infections contribute to transmission. We used a transmission model with asymptomatic and presymptomatic states, calibrated to data on disease onset and test frequency from the Diamond Princess cruise ship outbreak, to quantify the contribution of asymptomatic infections to transmission. The model estimated that 74% (70-78%, 95% posterior interval) of infections proceeded asymptomatically. Despite intense testing, 53% (51-56%) of infections remained undetected, most of them asymptomatic. Asymptomatic individuals were the source for 69% (20-85%) of all infections. The data did not allow identification of the infectiousness of asymptomatic infections, however low ranges (0-25%) required a net reproduction number for individuals progressing through presymptomatic and symptomatic stages of at least 15. Asymptomatic SARS-CoV-2 infections may contribute substantially to transmission. Control measures, and models projecting their potential impact, need to look beyond the symptomatic cases if they are to understand and address ongoing transmission.
Data availability
All data analysed during this study are included in the manuscript and supporting files. Model code is available through github.
Article and author information
Author details
Funding
European Research Council Starting Grant (Action Number 757699)
- Jon C Emery
- Rein M G J Houben
Wellcome (206250/Z/17/Z)
- Timothy W Russell
- Adam J Kucharski
Wellcome (208812/Z/17/Z)
- Stefan Flasche
Wellcome (210758/Z/18/Z)
- Joel Hellewell
- Sebastian Funk
Bill and Melinda Gates Foundation (INV-003174)
- Yang Liu
Bill and Melinda Gates Foundation (NTD Modelling Consortium OPP1184344)
- Carl AB Pearson
DFID/Wellcome Trust (Epidemic Preparedness Coronavirus research programme 221303/Z/20/Z)
- Carl AB Pearson
European Union Horizon 2020 (project EpiPose (101003688))
- Yang Liu
HDR UK (MR/S003975/1)
- Rosalind M Eggo
National Institute for Health Research (16/137/109)
- Yang Liu
Medical Research Council (MC_PC 19065)
- Rosalind M Eggo
Medical Research Council (MR/P014658/1)
- Gwenan M Knight
The funders had no role in study design, data collection and interpretation, or the decision to submit the work for publication.
Copyright
© 2020, Emery et al.
This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.
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The contribution of asymptomatic SARS-CoV-2 infections to transmission on the Diamond Princess cruise ship
eLife 9:e58699.
https://doi.org/10.7554/eLife.58699
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Background:
In many settings, a large fraction of the population has both been vaccinated against and infected by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Hence, quantifying the protection provided by post-infection vaccination has become critical for policy. We aimed to estimate the protective effect against SARS-CoV-2 reinfection of an additional vaccine dose after an initial Omicron variant infection.
Methods:
We report a retrospective, population-based cohort study performed in Shanghai, China, using electronic databases with information on SARS-CoV-2 infections and vaccination history. We compared reinfection incidence by post-infection vaccination status in individuals initially infected during the April–May 2022 Omicron variant surge in Shanghai and who had been vaccinated before that period. Cox models were fit to estimate adjusted hazard ratios (aHRs).
Results:
275,896 individuals were diagnosed with real-time polymerase chain reaction-confirmed SARS-CoV-2 infection in April–May 2022; 199,312/275,896 were included in analyses on the effect of a post-infection vaccine dose. Post-infection vaccination provided protection against reinfection (aHR 0.82; 95% confidence interval 0.79–0.85). For patients who had received one, two, or three vaccine doses before their first infection, hazard ratios for the post-infection vaccination effect were 0.84 (0.76–0.93), 0.87 (0.83–0.90), and 0.96 (0.74–1.23), respectively. Post-infection vaccination within 30 and 90 days before the second Omicron wave provided different degrees of protection (in aHR): 0.51 (0.44–0.58) and 0.67 (0.61–0.74), respectively. Moreover, for all vaccine types, but to different extents, a post-infection dose given to individuals who were fully vaccinated before first infection was protective.
Conclusions:
In previously vaccinated and infected individuals, an additional vaccine dose provided protection against Omicron variant reinfection. These observations will inform future policy decisions on COVID-19 vaccination in China and other countries.
Funding:
This study was funded the Key Discipline Program of Pudong New Area Health System (PWZxk2022-25), the Development and Application of Intelligent Epidemic Surveillance and AI Analysis System (21002411400), the Shanghai Public Health System Construction (GWVI-11.2-XD08), the Shanghai Health Commission Key Disciplines (GWVI-11.1-02), the Shanghai Health Commission Clinical Research Program (20214Y0020), the Shanghai Natural Science Foundation (22ZR1414600), and the Shanghai Young Health Talents Program (2022YQ076).
