
Nevertheless, diagnosing, preventing, and treating low Vit. D should be included in the COVID-19 prevention and treatment guidelines. It is still debatable if checking the 25-hydroxyvitamin D levels (25OH-D-a marker of Vit.

D might also act as an important cofactor of strengthening the activity of COVID-19 vaccines. D dosing in the COVID-19 era were proposed. D action in regard to COVID-19 infection were already discussed, and some suggestions for Vit. In the previous paper, the main mechanisms of Vit. D for COVID-19 patients, as it was also stated in two recent reviews. There is some evidence from clinical trials regarding the benefits of Vit.

D, in the form of calcitriol, has a pleotropic activity in human organism. It seems that there is a need for other effective tools for combating the COVID-19 disaster. The numbers of new COVID-19 cases and deaths from COVID-19 are increasing in many countries, despite the availability of different vaccines, more or less strict lockdowns or other state-level infection control measures, and various treatment options.
