Two layers of defence
The innate immune system responds quickly and generically — skin, mucus, and cells that attack anything foreign. The adaptive system learns: it builds antibodies and memory cells targeted to specific pathogens.
Immune memory
After an infection or vaccination, memory cells persist. If the same pathogen returns, the response is faster and stronger, which is the biological basis of immunity and of vaccination.
Limits of this overview
Immune function varies with age, medication and medical conditions. Questions about your own immunity belong with a clinician.