Vaccine and its types

July 18, 2018

INTRODUCTION OF VACCINE

Vaccine is a liquid chemical substance, which is used to stimulate an immune response in the body. It contains modified, inactivated or killed pathogens or their antigens. It is administered orally or injected in the body to stimulate the active immunity.

Immunity is defined as the ability of a body to resist diseases. Immunization of body through vaccination is generally done for the prevention of diseases. The vaccine is administered in advance so as to give the body time to set active immunity before invasion of the pathogen. When a pathogen enters the human body, it releases a toxic chemical to destroy the human defense system. This toxic substance is called antigen. Human blood defend themselves against and destroys that antigen by releasing a very specific chemical. This chemical is called antibody.

Small pox vaccine was the first successful vaccine to be developed which was introduced by Edward Jenner in 1796. Vaccine was derived from Latin vacca, meaning cow. A virus that mainly affects cows (cow pox) was used in the first scientific demonstration that giving a person one virus could protect against a related and more deadly one.

Later on the first experiment in immunization was performed by Louis Pasteur, a French chemist on July 6, 1885, when he treated a young boy against rabies. He extracted fluid from the spinal cord of a rabid dog and injected it in a small amount to the boy, who was bitten several times by a rabid dog. Apparently, the extract from the spinal cord had stimulated the production of antibodies against the rabies virus.

Dr. Jones Stalk, an American Physician developed a vaccine against poliomyelitis in mid-1950. He inoculated a boy against the disease and used a vaccine made from viruses which had been killed by formaldehyde.

TYPES OF VACCINES

The vaccines are of various types. They are as follows:

1) Live vaccines/ live-attenuated vaccines

In this type, the whole viruses are used or the viruses that are weakened or attenuated by chemical treatment are used so that they may induce immunity without causing the disease.
The method has been used in immunizing against rabies, yellow fever, small pox, polio, etc.

2) Dead organisms as vaccines

In some cases, the dead bodies of the pathogen, when injected into the host, stimulate the production of antibodies.
This does not cause any infection in the host.
This method has been used in immunizing against typhoid fever, whooping cough, and a few other diseases.

Image source: pubsrsc

3) Bacterial toxins and toxoid as vaccines

Exotoxins of most pathogenic bacteria are highly antigenic.
They stimulate the production of antibodies (antitoxins) in animal or human body.
These exotoxins are highly unstable and are converted gradually into toxoids during storage.
Toxoids retain the antigenic power but they are not toxin.
Therefore, they can be used in producing immunity against corresponding toxin.
Toxoids have been used to develop immunity against several diseases including diphtheria, tetanus, etc.

4) Cellular fractions as vaccines

Some vaccines are prepared from certain fractions of cell.
The meningococcal vaccine is produced from the polysaccharide antigen on the cell wall.
This vaccine is safe and effective but is only for a limited duration.
For examples: Pneumococcal polysaccharide vaccine, Hepatitis B polypeptide vaccine, etc.

Image source: mayoclinic

5) Recombinant vaccines

It is a vaccine produced through recombinant DNA technology.
In this vaccine, DNA encoding an antigen (such as a bacterial surface protein) is inserted that stimulates an immune response into bacterial or mammalian cells.
The antigen after being expressed in these cells release the antibodies which are then purified from them.
These are of three types: