<P> When B cells and T cells are activated by a pathogen, memory B - cells and T - cells develop, and the primary immune response results . Throughout the lifetime of an animal, these memory cells will "remember" each specific pathogen encountered, and can mount a strong secondary response if the pathogen is detected again . The primary and secondary responses were first described in 1921 by English immunologist Alexander Glenny although the mechanism involved was not discovered until later. This type of immunity is both active and adaptive because the body's immune system prepares itself for future challenges . Active immunity often involves both the cell - mediated and humoral aspects of immunity as well as input from the innate immune system . </P> <P> Naturally acquired active immunity occurs when a person is exposed to a live pathogen and develops a primary immune response, which leads to immunological memory . This type of immunity is "natural" because deliberate exposure does not induce it . Many disorders of immune system function can affect the formation of active immunity such as immunodeficiency (both acquired and congenital forms) and immunosuppression . </P> <P> Artificially acquired active immunity can be induced by a vaccine, a substance that contains antigen . A vaccine stimulates a primary response against the antigen without causing symptoms of the disease . Richard Dunning coined the term vaccination, a colleague of Edward Jenner, and adapted by Louis Pasteur for his pioneering work in vaccination . The method Pasteur used entailed treating the infectious agents for those diseases, so they lost the ability to cause serious disease . Pasteur adopted the name vaccine as a generic term in honor of Jenner's discovery, which Pasteur's work built upon . </P> <P> In 1807, Bavaria became the first group to require that their military recruits be vaccinated against smallpox, as the spread of smallpox was linked to combat . Subsequently, the practice of vaccination would increase with the spread of war . </P>

The type of immunity that results from a vaccination or infection