Brent Cornell

    
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

Vaccination

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

    
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

    
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

• These records are updated yearly and can be accessed at the following website:  WHO Data and Statistics

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:

• Reported Disease Incidence Time Series  (Excel file)
• Year of Introduction of Selected Vaccine  (Excel file)

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

⇒  Click on the diagram to swap between data table and graph