Origin and evolution of SARS-CoV-2.

SARS-CoV-2 is a novel coronavirus that emerged in China at the end of 2019 causing the severe disease known as coronavirus disease 2019 (COVID-19). SARS-CoV-2, as to the previously highly pathogenic human coronaviruses named SARS-CoV, the etiological agent of severe acute respiratory syndrome (SARS), has a zoonotic origin, although SARS-CoV-2 precise chain of animal-to-human transmission remains undefined. Unlike the 2002-2003 pandemic caused by SARS-CoV whose extinction from the human population was achieved in eight months, SARS-CoV-2 has been spreading globally in an immunologically naïve population in an unprecedented manner. The efficient infection and replication of SARS-CoV-2 has resulted in the emergence of viral variants that have become predominant posing concerns about their containment as they are more infectious with variable pathogenicity in respect to the original virus. Although vaccine availability is limiting severe disease and death caused by SARS-CoV-2 infection, its extinction is far to be close and predictable. In this regard, the emersion of the Omicron viral variant in November 2021 was characterized by humoral immune escape and it has reinforced the importance of the global monitoring of SARS-CoV-2 evolution. Given the importance of the SARS-CoV-2 zoonotic origin, it will also be crucial to monitor the animal-human interface to be better prepared to cope with future infections of pandemic potential.