Questioning the early events leading to the COVID-19 pandemic

Sixteen months after the January 30, 2020 declaration by the World Health Organization of a Public Health Emergency of International Concern regarding the spread of COVID-19, SARS-CoV-2 had infected ~ 170 million humans worldwide of which > 3.5 million had died. We critically examine information on the virus origin, when and where the first human cases occurred, and point to differences between Chinese and later clinical presentations. The official patient Zero was hospitalized in Wuhan, Hubei province, China, on December 8, 2019, but retrospective analyses demonstrate prior viral circulation. Coronaviruses are present in mammals and birds, but whether a wild animal (e.g. bat, pangolin) was the source of the human pandemic remains disputed. We present two contamination models, the spillover versus the circulation model; the latter brings some interesting hypotheses about previous SARS-CoV-2 virus circulation in the human population. The age distribution of hospitalized COVID-19 patients at the start of the epidemic differed between China and the USA-EU; Chinese hospitalized patients were notably younger. The first Chinese publications did not describe anosmia-dysgeusia, a cardinal symptom of COVID-19 in Europe and USA. The prominent endothelial involvement linked with thrombotic complications was discovered later. These clinical discrepancies might suggest an evolution of the virus.