What is the mechanism to make the RNA virus mutate to a deadlier disease?

Wouldn't the strains that are asymptomatic " rule the day?" Being allowed to propagate un abated?

It's a poor parasite that kills its host. Me thinks its eventually just gonna be another common cold.

Why do children seem less susceptible?


"Shoot low sheriff, I think he's riding a shetland!" B. Wills