What is vaccine? Types of vaccine.

Vaccine is an immunomodulator that prevents microbial infection. The first vaccine was discovered by Edward Jenner.

The vaccine came to us through an excellent history. The concept of vaccine came from a milkmaid woman. She informed Edward Jenner that “she had suffered from cowpox and never get smallpox”. This information leads Jenner to an experiment for developing vaccine.

In 1796, he collected scrapings from cowpox blister and injected into a healthy young boy. A few days later, the boy became sick and recovered soon and never got either cowpox or smallpox.

In 1880, Luis Pasteur found a bacterium avirulent which could cause fowl cholera (avirulence means lack of ability to cause disease). However, it and other microbes with decreased virulence were able to stimulate an immune response against subsequent infection by its virulent compartments.

Both experiments provide important message to later vaccination technology.


Definition of vaccine:

  • The vaccine is the suspensions of killed microorganisms, living attenuated microorganisms or living fully virulent organisms that are administered to produce or artificially increase immunity to a particular disease.
  • The vaccine is the preparation of microorganisms or fractions of microorganisms that are used to induce immunity in human or animal body.


Types of Vaccines:

Living attenuated vaccine:

  • These are suspensions of Living but attenuated (weakened) bacteria, viruses or other agents.
  • When administered by appropriate route to the human body, they cause subclinical or mild infection and thereby stimulates an immune response against the serious disease.
  • These vaccines give life-long immunity.
  • Attenuated viruses can replicate in the body, thereby increasing the original dose and stimulates a series of the secondary immune response.
  • Examples: Sabin polio vaccine against measles, mumps, and rubella (MMR); BCG against Mycobacterium bovis.

Killed vaccine:

  • These are suspensions of microorganisms fully killed by phenol, formaldehyde or by heat.
  • Killed vaccine can’t replicate and thereby doesn’t give life-long immunity.
  • These vaccines are poorly immunogenic.
  • Example: Polio vaccine, Rabies vaccine, Influenza vaccine.


Toxoid vaccine:

  • Toxoid vaccines are the suspension of inactivated toxins produced by pathogens.
  • In preparation of these vaccines, the toxin derived from bacteria is treated with a chemical (formaldehyde) to remove toxicity without removing immunogenicity.
  • Example: botulism, tetanus and diphtheria toxoid


Viral subunit vaccine:

  • Bacterial subunit vaccine is prepared by antigenic fragments of microbes, programmed by genetic modification to produce the desired antigenic fraction.
  • They provide the best stimulation of an immune response.
  • As they can’t reproduce in the recipient, are generally safer than other vaccines.
  • Example: Hepatitis B virus vaccine is produced from a portion of the viral protein coat by genetic modification of yeast or mammalian cells.


Nucleic acid vaccine:

  • These are the suspension of a plasmid of naked DNA.
  • When injected into the muscle, results in the production of the protein antigen encoded in the DNA.
  • The protein antigen stimulates both humoral and cellular immunity.
  • Example: Vaccine against West Nile virus.

Conjugated vaccine:

  • The conjugated vaccine consists of poorly immunogenic antigen is conjugated chemically with more immunogenic carriers to provoke an effective immune response.
  • They are widely applied in the prevention of infection, tumor therapy, fertility control and treatment of addictions.
  • Example: diphtheria toxoid is the conjugation of polysaccharide and protein; other conjugated vaccines are lipid-protein, alkaloid-protein, protein-protein, peptide- protein conjugated vaccine.


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