Two viruses have been entirely eliminated in the wild, one (Smallpox) still exists in government research facilities the other (Rinderpest) I believe is just gone because it wasn't useful as a direct weapon (humans aren't affected) and nobody actually wants Rinderpest, it was just killing cattle and while poor farmers need their cattle or they'll starve the rich want to drink milk and eat steak so they weren't keen on this virus either and helped fund its eradication.