Why didn’t things like polio and smallpox mutate as much or as dangerously?

Question

Why didn’t things like polio and smallpox mutate as much or as dangerously?

In: Biology

Answer 1

Different types of viruses mutates at different rates. Viruses like Rhinovirus and Coronavirus is known to mutate very fast which helps them avoid the immune system. But the changes means they only last for a short while, maybe just two years, before being out-competed by a new variant of themselves. However viruses such as polio and smallpox have a much more protected way of reproducing which does not cause as much mutations and we can therefore find largely unchanged viruses a hundred years later.