+1 ^^^

i reckon if you want to stay well in winter or any other season you gotta do more than just one thing... you gotta fully change your lifestyle and have lots of discipline and strong will... but once you master it all you feel invincible. You still may catch virus if you share salive with an infected person, but you'll get over it very quickly with less side effects.
My 2 cents is one needs to do
all of the below as one or two things is not enough:
- regular solid exercise (no escuses or skippin sessions)
- eat balanced and healthy as much as possible (some natural remedies are good - although i personally wouldn't go with any kinds of pills - only pure extracts etc...)
- avoid junk food, mcdonalz, sugar drinks, coffee, alcohol, drugs
- personal hygene and avoid crowded places during flu seasons
- have balanced family life, good relationships
- don't put your self in big financial pressures as much as possible
- have a consistent sleeping routine by getting sufficient sleep
- go to bed early and wake up early
- be positive and don't hang out with negative whinners
- have fun hobbies (i.e. sports, kiting, surfing, windsurfing, skateboarding, anything)
- do all of the above for a long period before seeing results (i.e. takes many months to build up strong body and immune system - especially after decades of bad habbits)