Does vitamin c, zinc, and vitamin d help protect against severe covid-19?

Maybe: The American Association of Physicians & Surgeons published a monograph this Fall(2020) suggesting this based on studies & treatment patterns of the authors. They may provide a fractional benefit to susceptible persons but the data is preliminary at best. If you add this to protective behaviors/sanitizing hands & the vaccine you may be protected. D taken in excess can create problems.

Prevention: The medications you mentioned may be helpful, however preventing infection by wearing a mask, social distancing and hand hygiene is far more important. Take Covid vaccine at the earliest opportunity (I did). Wish you good health!