Main article: Timeline of the 2019–20 coronavirus pandemic
Cases by country plotted on a logarithmic scale
There have been various theories as to where the first-ever case, or patient zero, may have originated. The first known case of the novel coronavirus was traced back to 1 December 2019 in Wuhan, Hubei, China. A later unconfirmed claim, citing Chinese government documents, suggests that the first victim was a 55-year-old man who fell ill on 17 November 2019. Within the next month, the number of coronavirus cases in Hubei gradually increased to a couple of hundred, before rapidly increasing in January 2020. On 31 December 2019, the virus had caused enough cases of unknown pneumonia to be reported to health authorities in Wuhan, the capital of Hubei province, to trigger an investigation. These were mostly linked to the Huanan Seafood Wholesale Market, which also sold live animals; thus the virus is thought to have a zoonotic origin.
During the early stages, the number of cases doubled approximately every seven and a half days. In early and mid-January 2020, the virus spread to other Chinese provinces, helped by the Chinese New Year migration, with Wuhan being a transport hub and major rail interchange, and infections quickly spread throughout the country. On 20 January, China reported nearly 140 new cases in one day, including two people in Beijing and one in Shenzhen. Later official data shows that 6,174 people had already developed symptoms by 20 January 2020.
On 10 January, based on reports from Chinese authorities, the WHO issued a travel advisory asking travellers to “be prudent to reduce the general risk of acute respiratory infections while travelling in or from affected areas (currently Wuhan City)”. While noting that the mode of transmission of the virus was unclear, it advised “against the application of any travel or trade restrictions on China”. On 12 January, based on additional information from the Chinese National Health Commission, WHO stated that “at this stage, there is no infection among healthcare workers, and no clear evidence of human to human transmission.” On 24 January, WHO updated its travel advisory by recommending entry and exit screenings while continuing to advise “against the application of any restrictions of international traffic”.
On 30 January, the WHO declared the outbreak to be a Public Health Emergency of International Concern. On 24 February, WHO director Tedros Adhanom warned that the virus could become a global pandemic because of the increasing number of cases outside China.
On 11 March, the WHO officially declared the coronavirus outbreak to be a pandemic, following a period of sustained community-level transmission in multiple regions of the world. On 13 March, the WHO declared Europe to be the new centre of the pandemic after the rate of new European cases surpassed that of regions of the world apart from China. By 16 March 2020, the total number of cases reported around the world outside China had exceeded that of mainland China. On 19 March 2020, China reported no new domestic cases (excluding cases re-imported from abroad) for the first time since the outbreak, while the total number of reported deaths in Italy surpassed that of China.