COVID-19 studies:  C19 studies: C19:  IvermectinIVM Vitamin DV.D HC QHC Q Vitamin CV.C ZincZn PVP-IPVP-I FLVFLV REGNR2 LY-CoVLY RemdesivirRMD
Vitamin D meta
1/5 Pre-Exposure Prophylaxis study (treated before exposed to the virus)
Nikniaz et al., medRxiv, doi:10.1101/2021.01.04.21249219 (Preprint) (meta analysis)
The impact of vitamin D supplementation on mortality rate and clinical outcomes of COVID-19 patients: A systematic review and meta-analysis
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Meta analysis of 4 supplementation studies, finding that vitamin D supplementation "seems to decrease the mortality rate, the severity of the disease, and serum levels of the inflammatory markers". Mortality odds ratio OR 0.264, p = 0.008.

Nikniaz et al., 1/5/2021, preprint, 4 authors.
risk of death, 67.5% lower, RR 0.32, p = 0.008, treatment 13 of 123 (10.6%), control 17 of 67 (25.4%), odds ratio converted to relative risk.

Effect extraction follows pre-specified rules prioritizing more serious outcomes. For an individual study the most serious outcome may have a smaller number of events and lower statistical signficance, however this provides the strongest evidence for the most serious outcomes when combining the results of many trials.
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