You just make stuff up. Immunity is not an absolute when it comes to disease.
Immunity:
noun
- the ability of an organism to resist a particular infection or toxin by the action of specific antibodies or sensitized white blood cells.
"immunity to typhoid seems to have increased spontaneously"
The word "resist" suggests that immunity has gradients. If immunity were absolute it couldn't "increase spontaneously".
Virtually immune means immune for all intents and purposes. Kids rarely get sick with covid 19 and they rarely transmit it. Virtually immune.