did you read the link i provided? in case the implication wasn't clear i'll say it explicitly. Viruses which are virtually nonexistent (not circulating in the population) can be induced in a population by vaccination itself (in rare cases when using an attenuated virus).

This means there is a risk, especially for viruses like polio which basically don't exist anymore, that a vaccination program will generate polio cases which then spread and create a new outbreak of polio.

Those recent outbreaks of polio were thought to be from an unnecessarily aggressive vaccination program, at least that's the reporting i encountered.

I haven't done a risk calculation, i don't claim to be an epidemiologist or to know at what point this exotic risk outweighs the benefit of herd immunity. I suspect that calculation depends on things like exposure points in the population, general immunity, and the %of people already vaccinated historically.

It's definitely a real effect (i linked directly to the american CDC) and it should be included in any discussion concerning virtually dead viruses. It hasn't been made up by 'antivaccers' and for me personally i don't even bring this up in those kind of spaces because i don't trust them to parse this level of nuance and contradiction to be brutally honest.

The risk profile probably varies virus to virus also.