COVID-19 mortality risk correlates inversely with vitamin D3 status, and a mortality rate close to zero could theoretically be achieved at 50 ng/ml 25(OH)D3: Results of a systematic review and meta-analysis

ConclusionsThe two datasets provide strong evidence that low D3 is a predictor rather than a side effect of the infection. Despite ongoing vaccinations, we recommend raising serum 25(OH)D levels to above 50 ng/ml to prevent or mitigate new outbreaks due to escape mutations or decreasing antibody activity.

“Long before the SARS CoV 2 pandemic, an increasing number of scientific publications showed the ffectiveness of a sufficient vitamin D3 blood level in curing many of the human diseases caused by a weak or unregulated immune system”

The finding that most SARS CoV 2 patients admitted to hospitals have vitamin D3 blood levels that are too low is unquestioned even by opponents of vitamin D supplementation.
Our results therefore also confirm the importance of establishing vitamin D3 supplementation as a general method to prevent severe courses of SARS CoV 2 infections.”
https://www.medrxiv.org/content/10.1101/2021.09.22.21263977v1.full.pdf+html