Once again, having vitamin D levels within the recommended range correlates with many aspects of _general health_. It does not have any _specific_ influence on

Once again, having vitamin D levels within the recommended range correlates with many aspects of _general health_. It does not have any _specific_ influence on influenza viruses. Not only is it not specific, but taking vitamin D doesn't directly do anything except raise one's existing vitamin D levels. If you don't understand the difference between A) the general health benefits of not being deficient in a vitamin/mineral/amino-acid/etc., and B) a _specific_ vaccine's effects against a _specific_ pathogen (or group of pathogens), I don't know what else to tell you.