I haven’t deleted any blogs, actually. What an odd thing to say.
Influenza can easily be spread through things like coughing and sneezing, making it virtually impossible to eliminate with basic precautions such as hand washing. Infection control is, of course, important, but the flu is incredibly infectious so prevention through vaccination is an excellent additional measure of safety.
In terms of vitamin D, there’s decent evidence that supplementation for people with a deficiency is an effective method of reducing upper-respiratory tract infections. Note that this includes many things which are not the flu, like colds. The evidence for significant protection for people who do not have vitamin D deficiencies is somewhat more limited. Added to the fact that the benefit is ~10% reduction in the risk of getting the flu, and you’re much better off getting a safe and effective vaccine which is much more protective and substantially cheaper than supplementing your diet forever.