But it also should mean that the "immune" will not spread the disease much at all -- certainly not as much as the not-immune who get sick. This is the key thin

But it also should mean that the "immune" will not spread the disease much at all -- certainly not as much as the not-immune who get sick. This is the key thing about immunity. Also, though (re)exposure of the immune may trigger an immune system response, the individual might not notice the exposure or the immune system response.