The organization Grassroots health put out the results of 212 people that had the COVID-19 virus, roughly 50 each having a critical or severe or normal or mild outcome. The results were stunning. Nearly all with a high level of vitamin D level in the blood had a mild outcome, as opposed to those with a vitamin D deficiency.

Up to now vitamin D deficiency has mostly been a concern for the people with the following risk factors, but not as a virus fighter.
- Osteoporosis or other bone disorder
- Previous gastric bypass surgery
- Age; vitamin D deficiency is more common in older adults.
- Obesity
- Lack of exposure to sunlight
- Having a darker complexion
- Difficulty absorbing fat in your diet
It should be fairly simple and fast to expand this analysis to a larger sample of people that also include people with antibodies to COVID-19 but never showed any symptoms.
If this holds true, we did the exact wrong thing by keeping people indoors in hope to slow the spread. Instead we should have encouraged people to be outdoors as much as possible, still practicing hygiene and social distance, give vitamin D to all over 65 (4000 IU), to all obese and people of dark complexion.
This is by no means the only suggestion, but it is one more weapon in the arsenal to combat this virus.