Vitamin D3
Not only for Flu prevention, but also for prevention of many other diseases.
Here are two video clips as samples of info on this subject.
http://uk.youtube.com/watch?v=tT-hbwKJqyA
http://uk.youtube.com/watch?v=15ycdbSsnAU
PS: like MMS, Vit A, water, life - too much can do you in.
Moderation and Proper Knowledge when applying healing methods.
Even over-massaging could harm you... (not me, though)