My FIL tested positive for covid, Influenza and strep all at the same time. He is fairly healthy and recovered fine, but felt crappy for a couple weeks. “Immunity” is an often misused, misunderstood word. Less susceptible, more resilient might be better terms than immune.

Your body has created a blueprint for the next infection so it knows what to do, but there’s no guarantee of immunity. And when your system is already stressed, you’re at a higher risk of another infection causing you symptoms than if you weren’t already fighting something. Think AIDS, it’s actually a common virus/bacteria that kills you, not the HIV/AIDS itself.