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The point isn't what causes polio or meningitis. The point is how the symptoms have changed simply by the heads of the medical rewriting them.
It's like the sky has always been blue, is now, and always will be. But somebody came along and said the sky color is green.
It's like the flat earth people who say that there isn't any gravity. They say that the thing that holds people on the earth is density. They don't care that people are held on the earth by some force or whatever. All they care about is that it is called density rather than gravity.
The causes of polio and meningitis have always been the same forever into the past. The difference is the description of which symptoms make up polio and which ones make up meningitis. It's essentially a semantics game that the medical uses to cover up their failures so that they can keep on making money.
I understand the difference between 'semantic games' played by, for example, the medical community, and practicalities like whether a disease has been vanquished. The topic of polio actually is relevant to both issues.
The professional medical community follows the path of highest profitability. That includes redefining things in a way that leads to more potential profit, but that redefining in turn leads to a pollution of the paradigms themselves that are used to understand things.
When you say "The causes of polio and meningitis have always been the same forever into the past", you are saying that you will buy some of what they are selling but not all. My point is that if they sell you rotten oranges you should examine the apples they are selling too.
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Worth noting too that there is an element of truth in everything even in lies. Flat earth people may talk about density but note that they know about the same amount about gravity as scientists, i.e., very little. Gravity is unique among fields in that it is most affected by the density of mass. The first assumption is that 'flat earth gravity' involves for example a person's density relative to water being similar, therefore less 'flat earth gravity' when a person is in water. But then you notice that means less gravity when the medium is more dense. So the flat earthers may seem to have a useless theory at the moment, but they have a 'foundation of physics' that may be more solid, with regard to gravity, than ours.