Which is in the same order of magnitude as other RNA viruses. Evolutionary rates of human influenza A: 1.8 × 10−3 to 2.2 × 10−3 Even lower than some kinds of flu viruses. So Nakagawa & Takayuki Miyazawa Inflammation and Regeneration volume 40, Article number: 17 (2020) Virus Evolution, Volume 6, Issue 2, July 2020, veaa061, J Virol. 2006 Apr; 80(7): 3675–3678.
in sequence. E.g. CAG codon wrong nucleic acid get added to the chain (CCG) glutamine-to-proline Genomes that differ in sequence are often called variants. Variants could differ by a single or many mutations. A variant is a strain when it has a demonstrably different phenotype e.g. difference in transmissibility, virulence or antigenicity, Mutation Variant Strain