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SARS-CoV-2 virus, known as COVID-19, was declared a health emergency towards the end of 2019 following an outbreak in the Chinese city of Wuhan. However, the results of water analyses gathered later from various parts of the world suggest it was already circulating before then. Initially, it presented as an acute health problem that spread from the original outbreak in Wuhan to other major metropolitan regions in China, particularly Shanghai, Chongqing and the Pearl River Delta (Guangzhou, Hong Kong, Shenzhen, etc.). Analyses of this expansion from data on public transport use, particularly the high-speed train –despite the small amount of data available from China–, explain the pandemic’s rapid spread throughout its vast territory. During the final months of 2019, it appeared the spread of the infection would be limited to China and to a few of its neighbouring Asian countries. However, international airports eased its spread to the rest of the world, and the World Health Organisation (WHO) declared it a global pandemic in early March 2020. The spread of the pandemic may be observed on the map on the ''[[:File:origins and spread of COVID-19|''origins and spread of COVID-19]]'']] , which shows the number of cases per country and month from February to July 2020. The peak of infections was registered in early April 2020. The lack of effective treatments for severe cases and little knowledge of how COVID-19 was transmitted during that period meant that it proved to be a highly lethal disease that resulted