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What are vaccines?

Vaccines are biological preparations containing agents that resemble specific diseases, using lower strengths and weakened forms of a particular microbe or toxin. Safety and efficiency are the two main aspects that are taken into account when developing new vaccinations (Plotkin & Mortimer, 1988). The safety of a vaccine all depends on how harmful the substance is in being able to affect an individual either directly or indirectly. Vaccine effectiveness is defined as the regulation of biological products, whereby the vaccine is tested for its immunological effects, its toxicities and both metabolic and pharmacological effects.

How vaccines work?

Vaccinations/ immunisations given to either children or adults are introducing the body to new antigens by allowing the immune system to adapt and develop a host defence against a particular virus or disease, without making the individual ill (Plotkin & Mortimer, 1988). This leads to the production of antibodies to a particular antigen, which is able to remain in the body protecting the body from any exposure or contact to the particular antigen.


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Figure: The immunity pathway for both active and passive immunisations.

Vaccines are divided into two broad categories, active and passive vaccines.
Active Vaccines:
They are the vaccines that are able to stimulate an immune response to specific antibodies and cellular immune responses. The main target for active vaccines is the ability to achieve a successive state of immunity against the host (Plotkin & Mortimer, 1988). Active vaccines are divided into two main categories:

Live vaccines:
  • Are microorganisms that function as immunogen and are able to infect cells by replicating their host without causing any natural diseases.
  • Attenuate in pathogenicity.
  • Elicit humoral and cellular immunity by the requirement of only fewer doses for complete defence/ immunity then other vaccinations.
  • Generally provide longer lasting immune protection.
  • Examples of live vaccines available: measles, mumps, bacilli and vericella vaccines.

Killed vaccine (non-live vaccine):
  • Unable to infect and replicate cells within the host.
  • Killed vaccines are not capable of multiplying or reverting to pathogenicity.
  • They are generally less reactogenic and non-transmissible to another person.
  • Examples of killed vaccines are the ones that are given to younger children, which include Hepatitis A and Tick-borne Encephalitis.


Passive Vaccines:
Passive vaccinations consist mainly of antibodies, providing protection against a specific pathogen or disease, which can be managed before or around the same time of a known potential exposure.


Vaccine Immunogenicity Neonatal Immune System : Adolescent Immune System : Adult Immune System´╗┐´╗┐´╗┐References Contributed by Rana Hamoud