I am curious about cross-immunity as it may pertain to all forms of influenza, pneumonia, coronaviruses, and SARS.

Aside from the discussed comorbidities and susceptibilities due to immune weaknesses and disorders, would someone who has never gotten severely ill have a smaller chance of being affected by Covid-19, the variants, and/or ADE?

I wonder if there may be natural or gained immunity with or without antibodies or T-cell immunity.

I bring it up because I don't remember having ever been severely bedridden for any length of time by such illnesses, nor do I take any prescription medications. Anyone else here experience or observe a similar potential correlation?