Vaccination

• Vaccination is the inoculation of material which generates protective immune responses and immunological memory.
• The immune memory provides protection following a subsequent exposure to the pathogen vaccinated against.
• Ideally vaccination should provide long-lasting and protective immunity against the pathogen in question.
• Live attenuated vaccines:

  • Attenuated organisms with reduced pathogenicity
  • Different attenuation methods
  • Stimulate immune response without causing disease
  • Some may replicate within the host to limited extent
  • Often more immunogenic than other vaccine types
  • May not be suitable for immunocompromised
  • Theoretical risk of return to virulence
• Killed or Inactivated Vaccines:

  • Whole killed organisms that do not cause disease or replicate
  • Different mechanisms for inactivation
  • Less immunogenic than live attenuated
  • Often require use of an adjuvant
  • Can impact safety
  • More stable
  • Can be used in immunocompromised
• Subunit vaccines:

  • Based on component of pathogen (antigen)
  • Proteins or peptides
  • Produced synthetically or derived/isolated from organism
  • Prior knowledge of which components of pathogen are antigenic required
  • Less immunogenic than live attenuated
  • May require use of adjuvant
  • Can be used in immunosupressed
• Recombinant or vectored vaccines:

  • Utilise host organism as carrier for antigen
  • May or may not replicate within host
  • Highly immunogenic
  • Prior knowledge of which components of pathogen are antigenic required
  • May not be suitable for immunosuppressed
  • Immune response may be directed at carrier rather than pathogen
• DNA or RNA Vaccines:

  • Based on RNA or DNA sequence of pathogen
  • Delivered as plasmid or mRNA
  • Translated into protein in the host cell
  • Can be rapidly degraded (poor stability)
  • May require carrier
  • Can be developed quickly
• Adjuvants are substances added to a vaccine to enhance the immune response. They are required for subunit vaccines as they are usually not very immunogenic. They also stir up the innate immune response which causes inflammation in some cases. Common examples are aluminium hydroxide or aluminium phosphate.