COVID-19
The virus is thought to be natural and has an animal origin,through spillover infection.The actual origin is unknown,but the first known cases of infection happened in China. By December 2019,the spread of infection was almost entirely driven by human-to-human transmission.A study of the first 41 cases of confirmed COVID‑19, published in January 2020 in The Lancet, revealed the earliest date of onset of symptoms as 1 December 2019.Official publications from the WHO reported the earliest onset of symptoms as 8 December 2019.Human-to-human transmission was confirmed by the WHO and Chinese authorities by 20 January 2020.