Nice post at Vitamin D Survivor April 2012

He graphed the CDC data of peak visits for influenza for a period of 15 years

Hypothesis: Less flu this winter because so many are now taking vitamin D

Baseline = rate during summer + 2 standard deviations

Mean % of patient visits for ILI during non-influenza weeks for the previous three seasons plus two standard deviations.”
This means that the incidence of the flu as defined through the outpatient flu surveillance network for this season was like it was summertime, or non-flu season.
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See also VitaminDWiki

• Overview Influenza and vitamin D which has the following graph

800 IU vitamin D is much better than vaccine, and 2000 IU vitamin D is far better