What happens if you have covid-19 but don't know it yet, and you get the vaccine?

Does getting the vaccine when you’re infected (but undiagnosed) change the way you respond to the vaccine?

Unless you take a test with practically instant results and in a known safe environment, how can you be sure you’re not sick when you get the vaccine? And does it make a difference?

Is this a risk associated with vaccination that we should be considering?