When a person gets sick, it probably means that the body has been infested by an infectious germ or virus, meaning that the immune system is already in a compromised, stressed-out state, working hard to remove the germ.
It’s common knowledge that a vaccine works the best when a person’s immunity is healthy, well-developed and stress-free.
Existing sickness, or at a time of sickness, when the immune system is already busy fighting out the virus would mean that there would be risks for the vaccine to work well, making many wonder if getting a COVID vaccine would be safe or not.
Not to forget, suffering from respiratory symptoms like cough, a fever could be doubly dangerous right now, since they are possible COVID symptoms as well. This is the only reason why some are being turned away from vaccination centres right now, because of the risk of infection spread.