Ah, that 'natural immunity' nugget. All immunity IS 'natural immunity'. Vaccines do not provide 'immunity' of any kind. They give your immune system a 'heads up'- this virus may be coming so get ready now. Create some antibodies so the cellular machinery is ready to crank them out if/when the real virus comes. Without exposure to something, such as a particular protein, that that virus carries, why would the immune system be prepared to fight it?

See, all natural. Except a vaccine provides an early warning to the body to be ready.