What is a Vaccine | 4 Types with Examples

A vaccine is a prophylactic medicine that is administered to prevent infectious diseases.

This vaccination is done for different diseases and can be given at any age.

The most commonly administered vaccines are for polio, TB, diphtheria, typhoid, pertussis, and measles.

These vaccines are administered as a means of resistance to various diseases.

Though expensive, many governments across the world provide free vaccination to their citizens to prevent communicable diseases.

This helps to counter infant death and increases citizens’ life span.

What is a Vaccine?

A Vaccine is a biological substance that is given to enhance immunity.

The body is made ready to combat and prevent corresponding infectious diseases in the future. It is a preventive health measure.

what is a vaccine

In a simple sense, the vaccine is given to healthy living beings to help their body to generate immunity against a specific infection.

This technology was developed as a preventive measure against rampant infection in the world. It is a type of biomimicry.

Without these vaccines, it would be difficult to combat many deadly infections like polio, smallpox, TB, etc.

Due to these vaccines, it was even possible to eradicate diseases like polio, and smallpox from many countries.

So what are vaccines made of

Vaccines are antigens that are extracted from specific disease-causing microbes.

These are administered to the healthy individual to prevent any further infection. So vaccines develop immunity for said disease.

How do vaccines work

The human body or any animal has an immune system that protects from diseases causing microbes and infections.

When a substance enters the bloodstream from outside the body other than the digestive route, the immune system gets alert to nullify and destroy the substance.

This foreign substance is identified by the size and also the nature of the chemical composition of the foreign particle.

Once the foreign substance is identified, the immune system develops antibodies and also triggers white blood cells, especially macrophages, to manage the foreign matter.

The antibodies bind to the foreign body and nullify it such that it does not cause any harm or disturbance to the body’s physiology.

Similarly, on the other hand, the macrophages engulf (eat) foreign particles like bacteria or protozoa if identified.

In case of weakness or stress, the body’s immunity is not sufficiently alert to recognize the foreign particle or disease-causing microbe.

In such cases, the microbe might become virulent and take over the body’s physiology such that even the immune system does not respond.

This leads to disease in the individual.

To prevent this, the body’s immunity is prior trained to defend against infections.

When vaccines (antigens or dead microbes) are administered to a healthy individual, the immune system produces suitable antibodies and macrophages to counter the antigens or microbes in the vaccine.

In doing this it develops immunity to the disease-causing microbe.

So in the future, if microbes for which vaccine were administered before infecting the person.

The immune system readily defends it and avoids diseases.

This trained immunity lasts for a few years to decades in most individuals.

So the administration of vaccines helps prevent infections in the future.

Types of vaccines

types of vaccines

There are 4 types of vaccines based on the type of antigen present in the vaccine.

Sometimes the whole microbe is given while only antigen from the microbe is given.

Live vaccine

As the name indicates, the vaccine is made of a real microbe, which has been made weak and devoid of virulence.

Here the microbe culture is treated such that it becomes weak and loses its ability to cause the disease.

The weakened microbe is administered into the body. In the body, it does not produce the disease, but instead, the immune system gets activated.

The antibodies and macrophages are produced so as to destroy the microbe.

Thus after the first exposure to the weak but live microbe, the body’s immune system is alert and can combat any future infections.
Ex: Polio vaccine

Dead Vaccine

Some of the microbes, like bacteria, are very virulent.

Even if they are weakened, they can quickly recover their virulent nature and cause diseases.

Hence to avoid this problem, the microbe is killed. The dead microbe is used as a vaccine.

The body develops immunity to this dead microbe based on the antigens present on the surface.

Ex: TB vaccine (BCG=Bacillus Calmette Guerin): Dead mycobacterium tuberculous bacteria is used.

Sub-unit vaccine

As the name indicates, here instead of the whole microbe, a part of it is taken.

This part is a sub-unit and has the potential to evoke a sufficient immune response.

This type of vaccine avoids the above problems of virulence and untoward infections.

Further, the sub-unit vaccines can be less expensive as only the part of the microbe is used.

This requires fewer procedures than the death of live vaccines

Genetically engineered vaccines

Most of the current vaccines fall into this category.

These are produced by using the principle of genetic engineering.

This type of vaccine lacks virulence and can also be produced on a large scale.

To cope with the vaccination demand of such a large population, it would be challenging to produce the above type of vaccines.

The vaccines of genetic engineering can be produced on a large scale by rDNA technology.

Also, they are less expensive and more compatible than previous ones.
Ex: Hepatitis vaccines.


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    • For leprosy there are no vaccines but since it is cause by mycobacterium lepra, BCG the one given to prevent TB (mycobacterium tuberculosis) is thought to be effective to prevent leprosy even.


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