I am a Clinical Lab Scientist and I have been data mining Vitamin D in acute respiratory infections and it's potential link to Sars Cov 2 Virus since ex CDC director Tom Freiden went on the news on March 23rd.  With that being said, this study in the article out of Chicago was not the first study linking Vitamin D deficiency to Covid 19.  I believe that designation with formidable proof goes to Dr. Mark Alipio from Indonesia.

Alipio, Mark, Vitamin D Supplementation Could Possibly Improve Clinical Outcomes of Patients Infected with Coronavirus-2019 (COVID-19) (April 9, 2020). Available at SSRN: https://ssrn.com/abstract=3571484 or http://dx.doi.org/10.2139/ssrn.3571484

With that being said, there is seemingly large amounts of pushback from the medical community and it is a little disturbing.  Yes I get it, the Medical societies really push real evidence based medicine, but there has to be a give and take given the safety for people to take 3000 iu of Vitamin D vs the potential risk of possibly getting severe Covid 19 manifestation should be a no brainer.  I mean good grief I do not recall anything every having this much and magnitude of circumstancial or anecdotal evidence and every day it becomes more and more.  Until the studies are done and complete what is the possible harm?  So we are willing to wait for direct evidence while houndreds of thousands die?  Ok, so the new oath in Medicine has transcended to "First do no harm" to "First do Nothing"