I'm not aware of a single working Covid-19 vaccine, which ones would that be? There are promising candidates, sure, but I don't think any have already been shown to be both effective and safe, which I'd say is required for one to be working, on the timescales that are needed, and I wouldn't know how one might do that so quickly. The current forerunners might well not work out, though I hope at least one of them will work, but my understanding is that anything immunity-related is fiendishly hard.