Introduction of Vaccine
- It 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 vaccine
- 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:
- Subunit recombinant vaccines
- Attenuated recombinant vaccines
- Vector recombinant vaccines
- For example: recombinant vaccine for Hepatitis B, subunit vaccines against HSV, etc.
Vaccine and its types