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Mechanistic-statistical SIR modelling for early estimation of the actual number of cases and mortality rate from COVID-19

By Lionel Roques, Etienne K Klein, Julien Papaix, Antoine Sar, Samuel Soubeyrand

Posted 24 Mar 2020
medRxiv DOI: 10.1101/2020.03.22.20040915

BackgroundThe number of screening tests carried out in France and the methodology used to target the patients tested do not allow for a direct computation of the actual number of cases and the infection fatality ratio (IFR). The main objective of this work is to estimate the actual number of people infected with COVID-19 and to deduce the IFR during the observation window in France. MethodsWe develop a mechanistic-statistical approach coupling a SIR epidemiological model describing the unobserved epidemiological dynamics, a probabilistic model describing the data acquisition process and a statistical inference method. ResultsThe actual number of infected cases in France is probably higher than the observations: we find here a factor x8 (95%-CI: 5-12) which leads to an IFR in France of 0.5% (95%-CI: 0.3 - 0.8) based on hospital death counting data. Adjusting for the number of deaths in nursing homes, we obtain an IFR of 0.8% (95%-CI: 0.45 - 1.25). ConclusionsThis IFR is consistent with previous findings in China (0.66%) and in the UK (0.9%) and lower than the value previously computed on the Diamond Princess cruse ship data (1.3%).

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