Re "olive leaf extract" yes I've used that myself. I am not aware of anything but anecdotal evidence in its favour, but it does seem to go well for me despite the disgusting taste.
Vitamin D and garlic are other things I have on a frequent basis, particularly if I feel anything coming on. The daily cost of these small items is next to nothing. Touch wood, I've managed to stay clear of anything too bad in years, despite commuting on trains with lots of people coughing etc ... remember those days before clown world paralysed our logic?
