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•  Vaccines contain antigens that trigger immunity but do not cause the disease

Vaccinations induce long-term immunity to specific pathogenic infections by stimulating the production of memory cells

  • A vaccine is a weakened or attenuated form of the pathogen that contains antigens but is incapable of triggering disease
  • The antigenic determinants in a vaccine may be conjugated to an adjuvant, which functions to boost the immune response
  • The body responds to an injected vaccine by initiating a primary immune response, which results in memory cells being made
  • When exposed to the actual pathogen, the memory cells trigger a more potent secondary immune response
  • As a consequence of this more potent immune response, disease symptoms do not develop (individual is immune to pathogen)

The length of time a person is immune to infection following a vaccination depends on how long the memory cells survive for

  • Memory cells may not survive a lifetime and individuals may subsequently require a booster shot to maintain immunity



Herd Immunity

Vaccinations programmes are implemented to reduce the outbreak of particular infectious diseases within populations

  • An epidemic is a substantially increased occurrence of a particular infection within a given region
  • A pandemic is an epidemic that has spread across a large geographical area (like a continent)

Vaccination confers immunity to vaccinated individuals but also indirectly protects non-vaccinated individuals via herd immunity

  • Herd immunity is when individuals who are not immune to a pathogen are protected from exposure by the large amounts of immune individuals within the community

herd immunity

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•  Smallpox was the first infectious disease of humans to have been eradicated by vaccination

Smallpox was the first infectious disease of humans to have been eradicated via vaccination

  • When a disease stops circulating in a region it is considered eliminated – if it is eliminated worldwide, it is considered eradicated

Smallpox was targeted for eradication in 1967 by the World Health Organisation (WHO), via a global vaccination programme

  • The last known case of smallpox in a civilian was registered in 1977 and it was officially declared eradicated by WHO in 1980

The eradication of smallpox by vaccination was successful for a number of reasons:

  • Smallpox was easily identifiable due to overt clinical symptoms, which helped to limit potential transmission
  • Transmission only occurred via direct contact and there were no animal vectors or reservoirs to sustain the infectious agent
  • The infection period was short lived (3 – 4 weeks) and the virus was stable and didn’t mutate into alternate strains
  • There was global cooperation and immunity was long-term so repeated booster shots were unnecessary

Eradication of Smallpox


TED Talks:  How we Conquered the Deadly Smallpox Virus

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•  Analysis of epidemiological data related to vaccination programmes

Vaccination programmes have lead to a reduction in the incidence of infectious diseases in a number of regions

  • Different nations will implement different vaccination practices depending on the regional pathogenic threats

The World Health Organisation keeps a record of disease incidence and immunisation schedules in different countries

Epidemiology is the study of the patterns, causes and effects of health and disease conditions in a defined population

  • It can be used to compare the incidence of a disease over time (prior and following vaccination programme implementation)
  • It can be used to compare the incidence of a disease in different regions (both with and without vaccination programmes)

Vaccination Data

The following resources can be used to generate data tables and graphs relating to national vaccination programmes:

When analysing trends associated with this data it is important to remember the following caveats:

  • Populations have increased year on year, which would be likely to increase the risk of potential outbreaks
  • Improvements to health care services, public sanitation and medical breakthroughs will also influence disease rates
  • Different regions may experience different levels of exposure to particular infections (due to climate and vector presence)

Incidence of Measles in Australia based on WHO Data Records

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  Click on the diagram to swap between data table and graph