Immunization is defined as the procedure by which the body is prepared to fight against a specific disease. It is used to induce the immune resistance of the body to a specific disease.
Immunization is of two types:
1. Passive immunization
2. Active immunization.
1. Passive Immunization
Passive immunization or immunity is produced without challenging the immune system of the body. It is done by administration of serum or gamma globulins from a person who is already immunized (affected by the disease) to a non-immune person.
Passive immunization is acquired either naturally or artificially.
Passive Natural Immunization- Passive natural immunization is acquired from the mother before and after birth. Before birth, immunity is transferred from mother to the fetus in the form of maternal antibodies (mainly IgG) through placenta. After birth, the antibodies (IgA) are transferred through breast milk.
Passive Artificial Immunization – It is developed by injecting previously prepared antibodies using serum from humans or animals. This type of immunity is useful for providing immediate protection against acute infections like tetanus, measles, etc.
Active immunization or immunity is acquired by activating immune system of the body. Body develops resistance against disease by producing antibodies following the exposure to antigens. Active immunity is acquired either ◦naturally or artificially.
Active Natural Immunization
Naturally acquired active immunity involves activation of immune system in the body to produce antibodies. It is achieved in both clinical and subclinical infections
Active Artificial Immunization
Active artificial immunization is a type of immunization that is achieved by the administration of vaccines or toxoids.
Vaccination : The process of distributing and administering vaccines is referred to as Vaccination.
Types of vaccine
1. Live-attenuated (weakened) vaccines
These vaccines contain modified strains of a pathogen (bacteria or viruses) that have been weakened but are able to multiply within the body and remain antigenic enough to induce a strong immune response. ( Replicating Ag). The varicella-zoster vaccine, oral poliovirus (OPV) vaccine, or yellow fever virus vaccine are some examples of this type of vaccine.
Advantage are- Single dose is sufficient for immunization
Heterologous vaccines: a sub-group of live attenuated vaccines produced from strains that are pathogenic in animals but not in humans.
-confers protective immunity against a pathogen that shares cross-reacting antigens with the microorganisms in the vaccine.
-Example cowpox virus that protects against smallpox in humans.
2. Killed- Inactivated Vaccines
To produce this type of vaccines, bacteria or viruses are killed or inactivated by a chemical treatment or heat. This group includes for example the inactivated poliovirus (IPV) vaccine, pertussis vaccine, rabies vaccine, or hepatitis A virus vaccine.
– Repeated dosing required.
3. Sub-unit vaccines
Instead of the entire microbe, subunit vaccines include only the antigens that best stimulate the immune system. In some cases, these vaccines use epitopes: the very specific parts of the antigen that antibodies or T cells recognize and bind to.
Because subunit vaccines contain only the essential antigens and not all the other molecules that make up the microbe, the chances of adverse reactions to the vaccine are lower.
Eg Hep B vaccine
4. Toxoid Vaccines: These vaccines are used when a bacterial toxin is the main cause of illness. When the immune system receives a vaccine containing a harmless toxoid, it learns how to fight off the natural toxin. ( non replicating Ag). The immune system produces antibodies that block the toxin. E.g Vaccines against diphtheria and tetanus.
Routes of Administration
Deep subcutaneous or intramuscular route (most vaccines)
Oral route (oral BCG vaccine)
Intradermal route (BCG vaccine)
Intranasal route (live attenuated influenza vaccine)
Scheme of immunization
One dose vaccines (BCG, measles, mumps, rubella, yellow fever)
Multiple dose vaccines (polio, DPT, hepatitis B)
To maintain immunity level after it declines after some time has elapsed (DT, MMR
Periods of maintained immunity due to vaccines
Short period (months): cholera vaccine
Two years: TAB vaccine (typhoid-paratyphoid A and B vaccine)
Three to five years: DPT vaccine (diphtheria, pertussis (whooping cough), and tetanus)
Five or more years: BCG vaccine(Bacillus Calmette–Guérin is a vaccine against tuberculosis)
Ten years: yellow fever vaccine
Solid immunity: measles, mumps, and rubella vaccines