The articles says reference for these data is a book called Vitamin D Revolution by Soram Khalsa, M. D (Amazon has 4.5 stars from 178 reviews).
Here and here are two books written by M.D.'s that support the health benefits of Vitamin D. If you need more references, I suggest searching for scientific reviews of Vitamin D literature (that is, if you have access to scientific journals). There's a mountain of evidence to support the immune modulating properties of Vitamin D. You're right to suggest that a single news article (with a somewhat sensationalist title) referencing a single scientific paper is weak ground to stand upon; it was literally the first result of a google search.