I hear what you're saying, but, who or what organization would else would do it? Individual countries struggle with it because, amongst other reasons, they're not as wealthy or stable as the US and Europe was when they beat (in this case) polio; they struggle to stay afloat, and they have bigger concerns for their people, base necessities like water, food and housing.
The UN? They (to me / personal viewpoint / citation needed) don't seem to have any power, influence, means or goodwill to handle a problem like this. I mean they have never been as silent as they are now, while China and the US have literal concentration camps, Russia is assassinating political opponents and is encroaching on other countries - directly (Ukraine) or indirectly (influencing governments, heavily influencing destabilizing decisions like Trump's election or Brexit), the US is in a civil war and on a crash course towards a fascist dictatorship, currently working towards a sham election, actively undermining postal services so mail voting will not work so that Trump can go "Well shit is fucked, I'll just stay on a bit longer to fix this for you" and declare national martial law so that the army can beat down whoever objects.