Healthy immune systems. #1 item is vitamin D. Almost everyone north of Florida is deficient. Take 10,000 iu per day (50 mcg). Will also prevent colds, the flu, and all other "seasonal" ailments. D will not prevent you from catching covid, but will keep it extremely mild, to the point where you may not be aware that you have it.

This info was known as early as April 2020 (when I read it). Almost all covid deaths were preventable.