BIOLOGY: VACCINES

BIOLOGY: VACCINES

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Overview

• A vaccine is a biological preparation that improves immunity to a particular disease
• Vaccines were first used by Edward Jenner (England) in the 1770s to inoculate against small pox using the cow pox microbe
• Vaccines have resulted in the eradication of small pox, one of the most contagious and deadly diseases known to man
• Other diseases like polio, measles, mumps, typhoid etc are have been significantly reduced. Currently, polio is prevalent in only four countries: Afghanistan, Pakistan, Nigeria and India
  Mechanism of action
• A vaccine is usually made from a weakened or dead form of the microbe that it is intended to fight
• It stimulates the body’s immune system to recognise the microbe as foreign, and destroy it and remember it
• When the same microbe re-appears later, the immune system easily recognises and destroys it
• When the body recognises the virulent microbe attack, it
  • Neutralises the target microbe before it can enter body cells
  • Destroys infected cells before the microbe can spread to other cells and multiply

Types of vaccines

• Killed vaccines: these are vaccines that contain micro-organisms that have been killed using chemicals or heat. Eg: influenza, cholera, bubonic plague, polio, hepatitis A
  
• Attenuated vaccines: these contain live attenuated (numerous) micro-organisms. These are usually live viruses that have been cultivated under conditions which disable their virulent properties, or use closely-related by less dangerous micro-organisms. These vaccines provide more durable immune response and are preferred type for healthy adults. Eg: yellow fever, measles, rubella, mumps, typhoid
  
• Toxoid vaccines: inactivated toxic compounds that cause illness. Eg: tetanus, diphtheria 
  
• Subunit vaccines: these use protein subunits instead of the entire micro-organism as a vaccine. Eg: Hepatitis B vaccine (which uses only surface proteins), Human Papilloma Virus (HPV) vaccine (which uses subunits of influenza virus)
  

Effectiveness of vaccines

• Vaccines do not guarantee complete protection from a disease
• This could be due to
  • Host’s immune system may not respond adequately
  • Host may have lowered immunity (such as due to diabetes, HIV, steroid use etc)
  • Host may not have a B cell capable of producing antibodies to that particular antigen
• The efficacy of a vaccine depends on a number of factors
  • The disease itself
  • The strain of vaccine
  • Following the schedule of vaccinations
  • Individual host factors
  • Genetic and ethnic predisposition
• Most vaccines use adjuvants to boost immune system response. Adjuvants are compounds added to the vaccine that increase the immune response, without having any specific antigenic effect by themselves. 
  
• Aluminum salts like aluminium phosphate and aluminium hydroxide are the most common adjuvants used
  
  

List of important vaccines

Vaccine	Disease	Type	Notes
Anthrax vaccine	Anthrax	Protein subunit
Bacillus Calmette-Guerin (BCG)	Tuberculosis	Live bacteria
DTP	Diphtheria Pertussis (whoopoing cough) Tetanus
Gardasil (Human Papilloma Virus (HPV))	Cervical cancer	Protein subunit
Polio vaccine	Polio	Killed/inactivated	Polio is prevalent only in humans Currently polio has been eradicated from all countries except Afghanistan, Pakistan, Nigeria and India
MMR	Measles Mumps Rubella
Meningococcal vaccine	Meningococcus
Rabies vaccine	Rabies	Attenuated
Yellow fever vaccine	Yellow fever	Attenuated

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JOHAR