the virus evolves to evade antibodies to prior versions - so even the fully vaccinated are not fully immune - but their risk of death, or serious illness is much much lower.
same goes for people with natural immunity from prior infection/s - these people are essentially naturally vaccinated
t-cell memory is much longer lasting and is not evaded by new variants to the same extent as prior antibody protection. so this is one of the mechanisms by which second and third infections are generally milder
its so ubiquitous over the last 12 months that its actually likely that we are actually getting infected and shrugging off other covid variants - in between the ones that give us symptoms- simply because our immune system recognises them as close enough to the first strain we had / vaccine - and deals with them without our even knowing.
each subsequent infection or vaccination for a different type builds our repertoire of recognised antibodies and t-cell responses - and improves our chances of having no - or mild symptoms when the next variant comes along.
this is mainly why disease outcomes of later variants tend to be milder
people with chronic illness with an immune dysregulation / inflammation and immune suppression component are of course at more risk for having more severe symptoms or lasting sequalae - that's just the nature of the beast
there are things we can do to improve our chances: eg.
-keeping our vitamin D levels in the ideal range
-supplementing with Zinc and Vitamin C
both have good scientific backing
iodine nasal sprays have demonstrated effectives at reducing chances of developing covid - eg could be used after suspected exposure
perhaps having some other treatment options on hand for if we do get it - eg
-ivermectin
others as listed by the COVID -19 critical alliance
https://covid19criticalcare.com/treatment-protocols/