Although I take Vitamin D and have for the past 5 years, I am not sure I see the correlation many make by suggesting those with higher Vitamin D levels are safer from Covid.

Might it just be that those 45-50+ that have low levels are on their way to some yet undiagnosed health problems, that can take time to develop, whilst those that monitor their health well and therefore keep up their levels are less likely to become ill all round?

That and/or ones natural Vitamin D levels decrease with age, again, past 45+, the same age group of people with underlying conditions or seniors. Many of whom may not yet be advised by their doctors to supplement.

That all being said, I wouldn't automatically add Vitamin D levels without blood tests to determine if one is low. In northern climates they suggest it during the winter months but those past 50 are still often naturally lower even in the summer months.
I take them year round despite being outside in the sun 5-8 hours daily