Betacoronavirus/classification; Animals; Betacoronavirus/genetics; COVID-19; Classification/methods; Coronaviridae/classification; Coronaviridae/genetics; Coronavirus Infections/epidemiology; Coronavirus Infections/transmission; Coronavirus Infections/virology; Genetic Variation; Genome, Viral; Humans; Nidovirales/classification; Nidovirales/genetics; Open Reading Frames; Pandemics; Phylogeny; Pneumonia, Viral/epidemiology; Pneumonia, Viral/transmission; Pneumonia, Viral/virology; Severe acute respiratory syndrome-related coronavirus/classification; Severe acute respiratory syndrome-related coronavirus/genetics; SARS-CoV-2; Severe Acute Respiratory Syndrome/epidemiology; Severe Acute Respiratory Syndrome/virology; Terminology as Topic; World Health Organization; Zoonoses