Fig. 1: Study design.

Flow diagram showing the number of subjects recruited in the calcifediol cohort (treated group) and the placebo cohort (placebo group) receiving intervention for 6 months, starting from the day of administration of the 1st dose of ChAdOx1 nCoV-19 (COVISHIELD) vaccine. Various biochemical and immunological parameters were investigated at baseline, 3rd month, and 6th month. For gene expression analysis, peripheral blood mononuclear cells (PBMCs) were isolated and analyzed at baseline, 3rd month, and 6th month.