Estimates of the severity of COVID-19 disease

Robert Verity; Lucy C Okell; Ilaria Dorigatti; Peter Winskill; Charles Whittaker; Natsuko Imai; Gina Cuomo-Dannenburg; Hayley Thompson; Patrick Walker; Han Fu; Amy Dighe; Jamie Griffin; Anne Cori; Marc Baguelin; Sangeeta Bhatia; Adhiratha Boonyasiri; Zulma M Cucunuba; Rich Fitzjohn; Katy A M Gaythorpe; Will Green; Arran Hamlet; Wes Hinsley; Daniel Laydon; Gemma Nedjati-Gilani; Steven Riley; Sabine van-Elsand; Erik Volz; Haowei Wang; Yuanrong Wang; Xiayoue Xi; Christl Donnelly; Azra Ghani; Neil Ferguson

For a given onset-to-death distribution, we then obtained a modelled estimate of the cumulative deaths by age under an age-dependent CFR (fitted relative to the CFR in the oldest age-group, which represented the largest number of deaths). This was compared to the observed deaths by age using a Poisson likelihood. These data were then jointly fitted alongside the most-recent age-aggregated cumulative deaths and cases in mainland China, fitted using a binomial likelihood. This follows from the observation that given the current situation, where both observed cases and deaths have dropped substantially following a peak in late January, the ratio of current cumulative cases, once corrected for under-ascertainment, to current death provide a good estimate of the final CFR 11 .