2018年に旧コロナNL63の重症患者が
突然増えたことがあったがこれも変異が原因
こういうことは度々ある
https://www.tandfonline.com/doi/full/10.1080/22221751.2020.1717999
https://www.tandfonline.com/na101/home/literatum/publisher/tandf/journals/content/temi20/2020/temi20.v009.i01/22221751.2020.1717999/20210405/images/large/temi_a_1717999_f0001_ob.jpeg