The defeat of polio proved that immunisation saved lives, but there's a sting to the tale

The rising number of vaccine-derived polio outbreaks has important implications for how we deal with Covid-19...
https://www.theguardian.com/global/2020/nov/15/the-defeat-of-polio-proved-that-immunisation-saved-lives-but-theres-a-sting-to-the-tale