Question

Why do we recover completely form a cold but not from polio?

Answer 1

The polio virus affects the nervous system.The cold viruses affect the linings of respiratory passages.

Explanation:

Polio virus and cold viruses work differently. A polio virus affects nervous tissue. Nerve tissue cannot undergo regeneration,except in a limited manner,so damages are for a lifetime.
The cold virus attacks the lining of the respiratory passage. This is made of tissue which is replaced throughout the lifetime of an individual.
https://en.wikipedia.org/wiki/Poliovirus
https://en.wikipedia.org/wiki/Common_cold