https://www.sciencedirect.com/science/article/pii/S0188440922000455?via%3Dihub

Even in a post-pandemic endemic COVID world, the rate of ongoing Covid infections is surprisingly high. We have certainly reached the point where it's become unmanageable illness, however still one that can be extremely disrupting to work and life routine. We're heading into indoor activities for several months, with the potential for higher rates of transmission. This article courtesy of the Kreser Institute weekly digest is a bit of good news in this forecast. Especially if you feel you need short-term protection to prevent an infection, it appears that a burst of vitamin D supplementation even in patients who are not vitamin D deficient may be helpful in warding off a symptomatic routine infection. The dose studied in this particular research article was 4000 IUs, which is going to be safe for almost everyone. However if you do choose to supplement, look at the total amount of vitamin D you're getting from a variety of sources. Many supplements that you may use for other purposes will have often some vitamin D added, so you want to know what your total is.