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

The first known case of Covid-19 has been traced back to December 1st, 2019 in Wuhan, the main city of the Hubei province of China [3] . The first death was reported on 11 January 2020. Most early cases were linked to the Huanan Seafood Wholesale Market in Wuhan, which was closed on 1 January. From this point, humanto-human transmission of SARS-CoV-2 occurred at a high rate in Wuhan and other areas of Hubei, leading to exponential growth of the reported incidence of Covid-19 cases ( Figure 1A ). On 20 January 2020, Chinese authorities implemented extensive control measures in Hubei: early identification and isolation of clinical cases, tracing and quarantining of contacts, temperature checks before accessing public areas, extension of the lunar new year holiday period, and extreme social distancing, including cancellation of mass gatherings [4] . Three days later, a cordon sanitaire was imposed, with strict traffic restrictions. From 27 January, the daily incidence of cases, by date of disease onset, started to plateau, then decreased. The number of reported deaths started to increase after the increase in incidence, with a delay of a few weeks.