Are pre-existing Vitamin D deficiencies linked to COVID-19 severity and mortality?

Even as the COVID-19 pandemic continues to spread and new variants of SARS-CoV-2 emerge, much remains to be known about why severity varies so unpredictably between individuals. A new study, released as a preprint on the medRxiv* server, elucidates the relationship between Vitamin D and COVID-19 severity.