Difference Between Active and Passive Immunity

Immunity is the capability to identify and respond to a foreign material and eliminate them from the body. When considering the human anatomy and physiology, it consists of two broad arms, namely, innate immunity and adaptive immunity. Innate immunity is the first line attackers against a foreign material, but it’s not specialized to specifically handle that foreign material. The adaptive immunity consists of humoral and cellular, and this type of immunity can be classified as active immunity and passive immunity. These two types differ in its origin, execution and the latent effects.

Active Immunity

As the name suggests, active immunity requires, a relatively healthy immune system to act as an antagonist against pathogens. Here, once the person is exposed to the organism, that person will develop immunity due to antibodies against that type of organism. There is a time lag between the inoculation of the pathogen to the release of antibodies. Finally, at the end of the battle, some of the cells formed in the initial exposure become memory cells, which would get activated in a massive scale if that person should get exposed to that organism again. The active immunity is again divided into two sub divisions. This would be the natural active immunity and the artificial active immunity. It is named as natural because, the person develops the full fledged infection to the organism and later finds himself resistant to that organism. In the artificial immunity, the patient is introduced with an organism (usually attenuated) along with substances to activate the immune response.

Passive Immunity

Passive immunity on the other hand, doesn’t require a healthy immune system as already formed antibodies are released directly into the circulation or to an area closely related to the affected site. Here, it is facilitative for an infant with a still developing immune system, or a person with a compromised immune system, or someone who requires back up till the active immunity kicks in. But, there is no activity by the immune system of that person, thus, it is only helpful for a shorter duration. This is again divided into two arms, natural and artificial. The natural passive immunity occurs, when the maternal Ig G type antibodies is passed to the foetus through the placenta. It is very much helpful in the initial 6 months of the infant’s life when the immune system is still developing. In the artificial passive immunity, we are introducing immunoglobulin or pre formed animal based antibodies (antiserum) to a non immune person. This can be used, following exposure, to a pathogen.

Active Immunity vs. Passive Immunity

If you consider active and passive immunity, the final outcome is implemented through antibodies and the cascade of activities initiated by these antibodies. These two types complement each other, and have a synergistic effect. But, the active immunity is only taking effect in a person with a healthy immune system, whereas, the passive immunity doesn’t. The active immunity cascade is initiating from an antigen, whereas, the passive immunity is always starting off with the antibodies. Active immunity has a lag period to act, whereas, passive is active from the start off. The antibodies developed from the active immunity are highly specific to that serotype or serovar, but the passive immunity based antibodies are not that specific because of its external origin and prone to early destruction due to this external origin. The immunity developed through active means is long lasting/ lifelong creating a person relatively resistant to a second exposure, whereas, immunity developed through passive means is of very short duration, thus, a person not resistant to a second exposure.

In summary, though it takes some time to act, active immunity is rapid and effective in fighting off pathogens while conferring a long-lasting immunity. Passive immunity, with its quick action, is easily subdued and doesn’t confer a long-term immunity. These two types complement each other.