What are the different types of immunization?

There are 2 types of immunization – active and passive. 

Active immunization

Active immunization involves administration of vaccines that stimulate the immune system, the body’s nature defense mechanism. 

Vaccines are formulations that may contain one of the following: 

• Live but attenuated or weakened whole organisms that cannot cause diseases such as Chickenpox, Bacille Calmette-Guerin (BCG), and Ebola among others.
• Noninfectious viral or bacterial fragments.
• A toxoid, which is a toxin originally synthesized by bacteria but modified to be harmless.

On receiving the vaccine, the body’s immune system reacts by generating substances such as antibodies that identify and target the specific virus or bacteria present in the vaccine. When the vaccinated individual later encounters that same virus or bacteria, the immune system quickly produces these antibodies and other defensive substances to prevent or reduce the severity of the illness. 

Passive immunization

In passive immunization, a person is directly given antibodies that target a specific infectious organism or the toxins it produces. These antibodies are sourced from various places including:

• Pooled Human Immune Globulin: Blood collected from a large group of people, which contains a mixture of antibodies from different individuals
• Animal Serum: Blood or serum of animals, typically horses, that have developed immunity after being exposed to a particular organism 
• Hyperimmune Globulin: Blood from individuals known to have high levels of antibodies to a particular disease, either because they have been vaccinnated or are recovering from the disease
• Laboratory-Grown Antibodies: Cells (usually from mice) that are grown in the laboratory and produce antibodies

The protection provided by passive immunization is temporary, lasting only a few weeks until the injected antibodies are naturally eliminated by the body. Passive immunization is useful for individuals whose immune systems do not respond effectively to infections or for those who contract an infection before they can be vaccinated, such as after exposure to rabies through an animal bite. Additionally, passive immunization can be used as a preventative measure in circumstances where there is a higher likelihood of exposure but no time to receive the complete vaccination dose. This can be seen in the case of a vaccination that targets chickenpox virus. This vaccination can be administered to pregnant woman who do not have immunity against the virus and have been exposed to it. Without immunization, the virus can harm the fetus as well as the mother.