On Polio "The fact that the virus can only survive in humans (and no other animals) makes it possible to completely eradicate the disease from the world – if it was a virus with an animal host such as influenza (birds) or tuberculosis (cows) that occasionally mutates to attack humans, polio could only ever be controlled but not eradicated."

Covid transmits in animals. CDC says based on current data, transmission to human is low (but not impossible) but more studies are needed. The fact they can get it is already not on the same scale as smallpox or polio.

https://www.cdc.gov/coronavirus/2019-ncov/daily-life-coping/...