I guess I was being overly broad. I'm not an immunologist or anything. I was thinking more of the kind of immunity one gets for something like chicken pox, whe

I guess I was being overly broad. I'm not an immunologist or anything. I was thinking more of the kind of immunity one gets for something like chicken pox, where one childhood infection basically protects you for life, vs something like the seasonal flu which you can get again and again. Now I don't know if the reason you keep getting the flu is because it mutates more rapidly than the chicken pox virus and you still remain immune to the particular strain you got infected with or if that initial immunity weakens over time. Maybe someone better informed can chime in.