> I think in most countries you're more likely to get polio from a polio vaccine than in the wild. On the one hand, that is a success of the polio vaccine. On the other hand, the vaccine is clearly dangerous and liable to cause chronic health problems.

In https://en.wikipedia.org/wiki/Polio_eradication#2025 I count 2 countries with the will type and 17 with the vaccine derived type (and like 160 without polio!)

There are two vaccines, the oral that has attenuated ("live") virus and the inyectable that has inactivated ("dead") virus.

* The oral version is not dangerous for the person that recibes it [1], but the virus can pass to other persons and after a few hops mutate to the dangerous version. The advantage is that the immunity is stronger and it also stops transmission.

* The inject able version is also not dangerous [1], it doesn't stop transmission, but it also can't mutate because the virus is totally dead.

Most fist word countries, and many other countries with no recent case use only the inyectable version. (Here in Argentina, we switched to only inyectable like 5 years ago :) .)

Countries with recent case of other problems use a mix, to reduce transmission. (I think the inyectable one is also cheaper and easier to store.) (Also, a few years ago they dropped globally one of the strains from the oral one, because that strains is eradicated. The inyectable one has that strains just in case, but it can't escape.)

[1] except potencial allergic reactions, that are rare, but I also remember big signs with instructions for the nurse explaining in case of an emergency what to do, what to inject, where to call ... The risk is not 0, but very low. I wonder if the trip to the hospital to get the vaccine is more dangerous.