Estimates of the population-level case fatality ratio from all case reports are in the range of 2–8%. Studies done solely in hospitalised patients report the highest fatality ratios (8–28%), representing the outcome for the most severely ill patients. Several studies have estimated the case fatality ratio (the percentage of individuals with symptomatic or confirmed disease who die from the disease) and infection fatality ratio (the percentage of all infected individuals who die from the disease, including those with mild disease) of COVID-19 using a range of different statistical and modelling methods. We searched PubMed, medRxiv, bioRxiv, arXiv, SSRN, Research Square, Virological, and Wellcome Open Research for peer-reviewed articles, preprints, and research reports on the severity of coronavirus disease 2019 (COVID-19), using the search terms “coronavirus”, “2019-nCoV”, and similar terms, and “fatality”, up to March 6, 2020. Similarly, estimates of the proportion of infected individuals likely to be hospitalised increased with age up to a maximum of 18♴% (11♰–37♶) in those aged 80 years or older.

Our estimated overall infection fatality ratio for China was 0♶6% (0♳9–1♳3), with an increasing profile with age. Estimates of case fatality ratio from international cases stratified by age were consistent with those from China (parametric estimate 1♴% in those aged <60 years and 4♵% in those aged ≥60 years ). However, after further adjusting for demography and under-ascertainment, we obtained a best estimate of the case fatality ratio in China of 1♳8% (1♲3–1♵3), with substantially higher ratios in older age groups (0♳2% in those aged <60 years vs 6♴% in those aged ≥60 years), up to 13♴% (11♲–15♹) in those aged 80 years or older. In all laboratory confirmed and clinically diagnosed cases from mainland China (n=70 117), we estimated a crude case fatality ratio (adjusted for censoring) of 3♶7% (95% CrI 3♵6–3♸0). Using data on 24 deaths that occurred in mainland China and 165 recoveries outside of China, we estimated the mean duration from onset of symptoms to death to be 17♸ days (95% credible interval 16♹–19♲) and to hospital discharge to be 24♷ days (22♹–28♱). Furthermore, data on age-stratified severity in a subset of 3665 cases from China were used to estimate the proportion of infected individuals who are likely to require hospitalisation. Using data on the prevalence of PCR-confirmed cases in international residents repatriated from China, we obtained age-stratified estimates of the infection fatality ratio. We also estimated the case fatality ratio from individual line-list data on 1334 cases identified outside of mainland China. We next obtained age-stratified estimates of the case fatality ratio by relating the aggregate distribution of cases to the observed cumulative deaths in China, assuming a constant attack rate by age and adjusting for demography and age-based and location-based under-ascertainment. These individual-case data were used to estimate the time between onset of symptoms and outcome (death or discharge from hospital). We collected individual-case data for patients who died from COVID-19 in Hubei, mainland China (reported by national and provincial health commissions to Feb 8, 2020), and for cases outside of mainland China (from government or ministry of health websites and media reports for 37 countries, as well as Hong Kong and Macau, until Feb 25, 2020). The Lancet Regional Health – Western Pacific.The Lancet Regional Health – Southeast Asia.The Lancet Gastroenterology & Hepatology.

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