Depends on the person, Iíll break this down by group.

Anybody with weak immune systems 2-4 times a year
Average immune system 1 time per year or 1 time every 2 years
Somewhat strong immune system 1 time every 2-5 years
Strong immune system 1 time every 5-10 years
Very strong immune system 1 time exceeding 10 years
Only about 2% of healthy people exceed 10 years without vomiting

(This is based off of individuals who donít have allergies to food, drinks, and medicine, plus who do not have any chronic illness)