Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible
and virulent human-infecting coronavirus that emerged in late December 2019 in Wuhan,
China, causing a respiratory disease called coronavirus disease 2019 (COVID-19), which
has massively impacted global public health and caused widespread disruption to daily
life. The crisis caused by COVID-19 has mobilized scientists and public health
authorities across the world to rapidly improve our knowledge about this devastating
disease, shedding light on its management and control, and spawned the development of
new countermeasures. Here we provide an overview of the state of the art of knowledge
gained in the last 2 years about the virus and COVID-19, including its origin and
natural reservoir hosts, viral etiology, epidemiology, modes of transmission, clinical
manifestations, pathophysiology, diagnosis, treatment, prevention, emerging variants,
and vaccines, highlighting important differences from previously known highly pathogenic
coronaviruses. We also discuss selected key discoveries from each topic and underline
the gaps of knowledge for future investigations.