Compared to the prime of life, as we age the stem cell populations in our body that get expanded to produce an antibody response inevitably decline. Mounting an active, acquired immune response (ie the ability to remember what you've been exposed to in the past and then producing the antibody response if re-challenged) becomes increasingly difficulty. Clean smart living can slow the decline, but within limits.
My take is the fear industry is largely self-manufactured, and is then exploitable, rather than the other way around. Look at the last two weeks of this thread. We are are on the downside of a global pandemic. In some ways we've been so, so lucky, but we did sorta-kinda manage to buy time for vaccines and those appear largely successful so far. First time in history. And yet its all about economic ruin, the tyranny of masks, why not bring in climate change too, government herding the sheeple, all that stuff. Don't really get it, but then I never liked "Goosebumps" either.