Take 3,000mg of vitamin C a day and you won’t have to worry about the flu or colds.
10,000 IU of vitamin D a day does the trick for me.
Not necessarily true for the typical cold or flu.
http://www.sciencedaily.com/releases/2007/07/070718002136.htm
If you are looking for a prophylaxis, Vitamin D would probably be more useful, as it has about a half dozen known antiviral actions.
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0011088
However, this is in the normal virus realm. H5N1 influenza is anything but normal.
To start with, it is a novel virus, so there is no immunity or partial immunity to it. This also means that it takes only a fraction of the amount of active virus to cause infection. Plus a very large pool of animal vectors, some with radically different immune systems.
It was the first real proof of the cytokine storm in which the immune system overreacts so violently that it kills the host. The later virulent H1N1 epidemic in Ukraine further proved its effects, the lungs of deceased victims looking black and burned.
Because of the lethality of H5N1, a lot of research went into finding an OTC chemical blend to lessen the Acute Respiratory Distress (ARD) associated with it as well as the virus itself.
The best approach to the virus was to hit it at all levels: keeping it out of the body; taking colloidal metals to inhibit viral reproduction; making cells ‘slick’ against the virus Hemagglutinin (the ‘H’ factor in H5N1), so they cannot attach and penetrate the cells; inhibiting viral reproduction within cells; inhibiting the viral Neuraminidase (the ‘N’ factor in H5N1), so the reproduced viruses cannot break out of the dying cell; having a vitamin D breakdown product in the blood that erodes the viral coat; having the proper immune response pathways open, again via Vitamin D; and Vitamin D as an ACE inhibitor to moderate the immune response.