sars-CoV-2 behaves like a monstrous mutant hybrid of all the human coronaviruses that came before it. It can infect and replicate throughout our airways. “That’s why it is so bad,” says Stanley Perlman, a professor of microbiology and immunology
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Once the virus is spreading easily within a species, though, its attitude is, “I’m happy, I’m good, no need to change,” Denison said.
That seems to be playing out now in humans; as sars-CoV-2 circles the globe, there are slight variations among its strains, but none of them seem to affect the virus’s behavior. 
“This is not a virus that is rapidly adapting. It’s like the best car in the Indy 500. It’s out in front and there is no obstacle in its path. So there is no benefit to changing that car.”
