Active immunity is defined as “the body’s natural ability to resist or defend itself against a pathogen, antigen or any other disease causing agent”. In contrast to passive immunity in which antibodies are injected to the organism, in active immunity the body itself produces antibodies capable of fighting against the disease causing agents.
Types of Active Immunity
There are two types of active immune response: naturally acquired active immunity and artificially acquired active immunity.
In naturally acquired active immunity, when a body is exposed to a live pathogen, it develops the disease and then its primary immune response starts to fight against the invaders. Whenever a microbe enters the body it is exposed to B-cells which produce antibodies in response and fight against it. This adaptive immune response may take days or even weeks to develop but is long-lasting or even lifelong. Because once the immune system learns to produce antibodies against a specific antigen, it can do so again and again, so the subsequent infections would be much less hazardous.
In artificially acquired active immunity, administration of a vaccine generates immunity. Vaccination or immunization is the intended induction of immune response and it the only most effective manipulation of the immune system developed by scientists. Vaccinations are almost always successful as they utilize the natural specificity of the immune system. The principle behind acquired active immunity is to introduce a dead virus or bacteria of a disease which though cannot produce the disease itself, but lets the body think of it as a disease-causing agent hence helps the immune system develop protective immunity against it. For example, the administration of Hepatitis A vaccine generates the artificially acquired immunity against Hepatitis and protects the body against real Hepatitis A virus in future.