Like covid is mutating and other virus common cold mutate too than why covid virus infection sevrity varies with mutation and common cold severity don't because common cold is same as from years?

Trophism is the term used to describe the target of a virus infection. The trophic site of the mumps virus is the glands in the cheek. Influenza B often attacks the calves. Covid 19 & delta attacked the deep lung tissue in most. The omicron variant appears to spare the lung in most & attack above the vocal cords/head/sinuses/etc. Mutations can change the trophism. We hope it leaves the lungs alone