The best Vitamin to take considering the current circumstances is Vitamin D. Vitamin D can reduce the risk of Covid. It can lower viral replication rates and also reduce concentrations of pro-inflammatory cytokines that produce the inflammation that injures the lining of the lungs, leading to pneumonia, as well as increasing concentrations of anti-inflammatory cytokines.
This was observed with SARS before. Elderly people were given injections of 10,000 IU to reduce risk.
Taking a capsule of 500 IU a day is recommended.