This one, I believe. I have been taking vitamin D supplements since March 2020. There is also a strong relationship between the regions of the world with low sun exposition and the COVID virus propagation.
>>> “The trial included 76 patients with COVID-19 pneumonia. Although this is no longer the standard of care, all patients were treated with hydroxychloroquine and azithromycin and, when needed, a broad-spectrum antibiotic. ”
chrismasterjohnphd.com/covid-19/finally-confirmed-vitamin-d-nearly-abolishes-icu-risk-in-covid-19