Early assessments of the growth rate of COVID-19 were subject to significant uncertainty, as expected with limited data and difficulties in case ascertainment, but as cases were recorded in multiple countries, more robust inferences could be made. Using multiple countries, data streams and methods, we estimated that, when unconstrained, European COVID-19 confirmed cases doubled on average every 3 days (range 2.2-4.3 days) and Italian hospital and intensive care unit admissions every 2-3 days; values that are significantly lower than the 5-7 days dominating the early published literature. Furthermore, we showed that the impact of physical distancing interventions was typically not seen until at least 9 days after implementation, during which time confirmed cases could grow eightfold. We argue that such temporal patterns are more critical than precise estimates of the time-insensitive basic reproduction number R 0 for initiating interventions, and that the combination of fast growth and long detection delays explains the struggle in countries' outbreak response better than large values of R 0 alone. One year on from first reporting these results, reproduction numbers continue to dominate the media and public discourse, but robust estimates of unconstrained growth remain essential for planning worst-case scenarios, and detection delays are still key in informing the relaxation and re-implementation of interventions. This article is part of the theme issue 'Modelling that shaped the early COVID-19 pandemic response in the UK'.
|Journal||Philosophical transactions of the Royal Society of London. Series B, Biological sciences|
|Early online date||31 May 2021|
|Publication status||Published - 19 Jul 2021|
Bibliographical noteFunding Information: L.P., H.B.S. and C.E.O. are funded by the Wellcome Trust and the Royal Society (grant no. 202562/Z/16/Z). K.A.L. is funded by the Wellcome Trust and Royal Society (grant no. 107652/Z/15/Z). F.S. is funded by the CIHR 2019 Novel Coronavirus (COVID-19) rapid research program. L.H.K.C. is funded by the BBSRC (grant no. BB/R009236/1). E.F. is funded by the MRC (grant no. MR/S020462/1). T.A.H. is supported by the Royal Society (grant no. INF\R2\180067). I.H. is supported by the National Institute for Health Research Health Protection Research Unit (NIHR HPRU) in Emergency Preparedness and Response and the National Institute for Health Research Policy Research Programme in Operational Research (OPERA). The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR, the Department of Health or Public Health England. L.P., T.A.H. and I.H. are also supported by The Alan Turing Institute for Data Science and Artificial Intelligence. L.P., T.A.H., I.H. and F.S. are also supported by the UKRI through the JUNIPER modelling consortium (grant no. MR/V038613/1).
Open Access: Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.
Publishing copyright:© 2021 The Authors.
Citation: Pellis Lorenzo, Scarabel Francesca, Stage Helena B., Overton Christopher E., Chappell Lauren H. K., Fearon Elizabeth, Bennett Emma, Lythgoe Katrina A., House Thomas A., Hall Ian and University of Manchester COVID-19 Modelling Group 2021Challenges in control of COVID-19: short doubling time and long delay to effect of interventions Phil. Trans. R. Soc. B3762020026420200264
- early growth rate
- incubation period
- non-pharmaceutical interventions
- onset-to-hospitalization delay
- reproduction number
- unconstrained epidemic