Why are we able to completely eradicate some viruses through vaccines but not others?

Question

Smallpox for example and Polio (almost)

In: 2

Answer 1

There are a huge number of things that need to fall into place to make a virus a candidate for eradication:

Lack of non-human vectors
Slow rate of mutation
Relatively cheap, stable and easily stored vaccine that provide long term immunity
Global effort to role out these vaccines nationwide, or even worldwide
Good disease surveillance

If any one of these pieces aren’t in place, then eradicating a disease is a hugely daunting task that you could be forgiven for saying is outright impossible.