I take a multi-vitamin daily along with C, D, E supplements. I have been taking these at the recommendation of my Dr. for several years - well before the pandemic. I also take Glucosamine (seems to help with the knees), and my wife talked me into Melatonin, which does seem to produce a deeper more restful sleep.
With this regimen I have been healthy for years. I have never had a flu shot, haven't had the flu in 25 years or so - literally can't remember exactly when the last time was but I can estimate. I haven't taken a sick day in years - when back and checked my time off / vacation tracking spreadsheet - February of 2015 I took 1 day. No other sick days off going back as far as the spreadsheet goes - to pre 2010.
Through work and hobbies I have been directly exposed (close contact per the CDC definition) to over a thousand people from across the country since the scam-demic started. Since most of them had recently flown in to town, that's indirect exposure to tens of thousands more people. I've never got the sniffles. Natural immunity works. Take your vitamins, get some exercise, get some sun, drink enough water and get enough rest. Humans have been fighting off infections since there have been humans.
It is such a terrible shame that this info hasn't been put out there in the last 2 years - but then the elites wouldn't get rich off of it so millions had to DIE!