What is natural active immunity?

Answer 1

Active immunity involves the production of antibodies (by B lymphocytes) and cell-mediated response (with T lymphocytes). It renders relatively longer immunity (compared to passive immunity). Active immunity may be natural or artificial.

This type of active immunity is said to be natural because the immunity is induced not by deliberate exposure (such as vaccination). The individual has developed immunity to a live pathogen by having been exposed to it and by developing a primary immune response that led to immunological memory.