One should mean that nature, God or whatever would have created the human body in a way that it can deal with any desease on its own with its own body's defenses and without having to inject some strange stuff.

We have to vaccinate because of that. Some diseases we can deal with, survive and develop immunity against, but others we can not, or there will be consequences even if we survive. Measles can affect things like hearing and eyesight, and polio can make you partly or completely paralysed, etc.

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So either the human body is a total failure of construction or there went something wrong along the way and we destroyed our bodies' defenses in a way that we now have to vaccinate.

To be sure we have done things that have had negative effects on our bodies, but that's not why we don't have Superman level immunity to everything.