Immunity is non-susceptibility that may be either congenital (genetically predetermined) or acquired (developed during the life after natural or artificially induced (immunisation) exposure to particular disease agents).

The immune system allows us to live and survive in this world, by protecting our body from everything that is strange and dangerous (bacteria, viruses, fungi, parasites, stress, radiation, non-systematic use of medications and other factors) and in the event of any extreme conditions.