It is well established that Vit D is important to a strong immune system, among other things.
It was observed early in the pandemic that most getting seriously ill from Covid were Vit D deficient. That same can probable be said for many infectious diseases.
Weird that the CDC (or most Western health agencies) never promoted Vit D for Covid prevention. Similarly they didn’t promote other low-cost healthy lifestyle choices (weight-loss and exerciser) that also significantly reduce the risk/harm from Covid.
Yeah, well... It’s all about MONEY. The CDC and FDA are criminal organizations in bed with big pharma. Politicians are bribed by pharma also.