The general population has vit-d deficiency, esp older and minority folks (in the US).
So doesn't explain the whole observed effect
Edit: also the study was in Spain, not USA
> Vitamin D deficiency was found in 82.2% of COVID-19 cases and 47.2% of population-based controls (p<0.0001).
You must adjust for age.
They may have done that too for all relevant factors but we’d need to read the paper.
In other words, you could read the line as "Vitamin D deficiency was found in 82.2% of COVID-19 cases and 47.2% of controls, when accounting for age (p<0.0001)."