After you’ve been exposed to a pathogen, antigen specific memory B Cells persist. If the pathogen reappears, they quickly pump out antibodies against that pathogen.
I have the impression that, when this happens, you can feel bushed. I’m not sure if that impression is correct, but it’s based on various times that I’ve been hanging around sick kids, doing things for them, without actually catching the flu or stomach bug they have. When I don’t catch it, seems likely it’s one that I’ve had before.
Does anyone know if there really is such a response?