SARS - CoV-2 is a new RNA virus
that ( i ) SARS - CoV-2 genomes are overall conserved under purifying selection .
SARS - CoV-2 is a new RNA virus affecting humans and spreads extensively through world populations since its first outbreak in late December , 2019 .
Interrogating 22,078 SARS - CoV-2 genome sequences of 84 countries , we demonstrate with convincing evidence that ( i ) SARS - CoV-2 genomes are overall conserved under purifying selection .