Adjusted age-specific case fatality ratio during the COVID-19 epidemic in Hubei, China, January and February 2020

Julien Riou; Anthony Hauser; Michel J Counotte; Christian L Althaus

Estimates of mortality from SARS-CoV-2 in China adjusting for bias vary. Our estimate for Hubei province is higher than the 1.38% estimated for mainland China [26] . Verity et al. used a similar approach to ours, but there are differences between the models. They considered all mainland China, where mortality appears to be lower than in Hubei province [27] . They assumed a homogeneous attack rate across age groups rather than simulating epidemics using an age-specific contact matrix, and assumed a reporting rate of only 70% for the elderly. Other studies that attempt to correct for right-censoring of deaths give higher estimates of mortality than in our study. A study using a competing risk model estimated mortality at 7.2% (95% confidence interval: 6.6%-8.0%) for Hubei province [28] . Using data on exported cases, another team estimated mortality of 5.3% (95% confidence interval: 3.5%, 7.5%) among confirmed cases in China [29] . Another team reported a CFR of 18% (95% credible interval: 11-81%) among cases detected in Hubei, accounting for the delay in mortality and estimated the overall CFR at 1% (95% CI: 0.5%-4%), based on data from the early epidemic in Hubei and from cases reported outside China [30] . Our estimate of mortality among all infected cases in Hubei is also higher than in an earlier version of this work (3.0% against 1.6%) [31] . We believe the newer estimate to be more reliable for two reasons. First, we implemented age-specific risks of transmission through a contact matrix, which partially explains the age patterns in reported Covid-19 cases and leads to lower estimates of the total number of infections, thus increasing mortality. Second, a higher estimated proportion of symptomatic people, based on new studies [19, 18] , also led to higher estimates of mortality among all infected.