Vaccine and its types

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.

A comprehensive overview of vaccines developed for pandemic viral pathogens  over the past two decades including those in clinical trials for the curre  ... - RSC Advances (RSC Publishing) DOI:10.1039/D0RA09668G

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.

Different types of COVID-19 vaccines: How they work - Mayo Clinic

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:
  1. Subunit recombinant vaccines
  2. Attenuated recombinant vaccines
  3. Vector recombinant vaccines
  • For example: recombinant vaccine for Hepatitis B, subunit vaccines against HSV, etc.

References: 

i) https://www.news-medical.net/health/What-are-the-Different-Types-of-Vaccines.aspx#:~:text=Subunit%2C%20recombinant%2C%20conjugate%2C%20and%20polysaccharide%20vaccines%20use%20particular%20parts,need%20topping%20up%20over%20time.

ii) https://historyofvaccines.org/vaccines-101/what-do-vaccines-do/different-types-vaccines

Vaccine and its types