Actually, there's a lot of data that suggests that it WILL prevent more hospitalizations and deaths than masking, which has very little supporting it. I don't know that there's any good data on the efficacy of distancing, though it stands to reason it will be pretty effective.
Feel free to go through the studies. The link is voluminous.
Research has found associations between low levels of vitamin D and increased risk for a range of health problems, including bone fractures, cardiovascular disease, diabetes, colorectal cancer, depressed moods, cognitive decline and impaired immune systems leaving them more vulnerable to a host of diseases or more severe illness for these diseases as well as COVID. Those with damage to their liver, kidneys, and with G.I. problems don't absorb or metabolize vitamin D adequately. Even obesity leads to reduced levels.
It has been established that those whose health is more compromised will be more likely to be hospitalized with more severe COVID and have higher rates of death. Correlation is not synonymous with causality. Low vitamin D may not be the primary cause of increased severity of COVID and its role may be overestimated by isolating this factor. Also, we don't yet have any information suggesting that those who are not deficient are more protected from COVID if they take supplements to increase their levels.
The relationship between Vitamin D and COVID is complex with many unknowns. One issue not yet determined is whether the COVID patients found to be deficient were also deficient before they were infected. IOW, COVID may have reduced their Vitamin D levels.
I'm confused by your statement that there's a lot of data suggesting vitamin D supplements will prevent more hospitalizations and deaths than masking. Please direct me to a comprehensive study with these findings. I think that's highly unlikely.