Vaccinations

• Vaccination


  A suspension of antigens that are intentionally put into the body to induce artificial active immunity
• Vaccines


  • Cause a specific immune response where antibodies are released by plasma cells
• Types of vaccines


  • Live attenuated
  • Inactivated
• Live attenuated vaccines


  Contain whole pathogens (e.g. bacteria and viruses) that have been 'weakened'
• Inactivated vaccines


  Contain whole pathogens that have been killed ('whole killed') or small parts ('subunit') of the pathogens (eg. proteins or sugars or harmless forms of the toxins - toxoids)
• Live attenuated vaccines tend to produce a stronger and longer-lasting immune response
• Live attenuated vaccines can be unsuitable for people with weak immune systems as the pathogen may divide before sufficient antibodies can be produced
• Inactivated vaccines do not contain living pathogens so they cannot cause disease, even for those with weak immune systems
• Inactivated vaccines do not trigger a strong or long-lasting immune response like live attenuated vaccines
• Repeated doses and/or booster doses are often required for inactivated vaccines
• Some people may have allergic reactions or local reactions (eg. sore arm) to inactivated vaccines as adjuvants (eg. aluminium salts) may be conjugated (joined) to the subunit of the pathogen to strengthen and lengthen the immune response
• Vaccine administration


  • Vaccines are administered either by injection or orally (by mouth)
  • Vaccinations given by injection can be into a vein or muscle
• Vaccination programmes


  Offered to citizens by the government as a major component of health protection
• Vaccines are given to the young in the population to protect them from diseases that were once common and caused serious harm
• International travel means there is the possibility that a disease could be reintroduced at any time by travellers coming from other countries
• By having their citizens vaccinated against diseases, governments can prevent serious epidemics from occurring
• Effectiveness of vaccines


  • Very few drugs are effective against viruses which is why vaccines are critical in controlling the spread of viruses
  • Vaccines can be highly effective with one vaccination giving a lifetime's protection (although less effective ones will require booster/subsequent injections)
  • Vaccines are generally harmless as they do not cause the disease they protect against because the pathogen is killed by the primary immune response
• Problems with vaccines


  • People having a poor response (eg. they are malnourished and cannot produce the antibodies-proteins or their immune system may be defective)
  • Antigenic variation-the variation (due to major changes) in the antigens of pathogens causes the vaccines to not trigger an immune response or diseases caused by eukaryotes (eg. malaria) have too many antigens on their cell surface membranes making it difficult to produce vaccines that would prompt the immune system quickly enough
  • Viruses having the capacity to change their surface antigens (the targets of vaccines) by: Antigenic drift, Antigenic shift, Antigenic concealment, Cross-breeding
• Herd immunity


  Arises when a sufficiently large proportion of the population has been vaccinated (and are therefore immune) which makes it difficult for a pathogen to spread within that population
• Herd immunity allows for the individuals who are unable to be vaccinated (eg. children and those with weak immune systems) to be protected from the disease
• The proportion of the population that needs to be vaccinated in order to achieve herd immunity is different for each disease
• If vaccination rates fall below the required level then herd immunity can break down
• Ring immunity


  People living or working near a vulnerable (or infected) person are vaccinated in order to prevent them from catching and transmitting the disease
• Challenges of eradicating disease

  • Some pathogens are simply complicated and present with disease processes that are not straightforward and so a successful vaccine has not been developed
  • Diseases that could be eradicated where a vaccine does exist, have not been eliminated because too few in the community have been vaccinated
  • Unstable political situations in areas such as Africa, Latin America and parts of Asia, perhaps resulting in civil unrest or wars
  • Lack of public health facilities (poor infrastructure, few trained personnel, limited financial resources)
• The eradication of Smallpox is a success story, but its success had specific reasons that cannot be universally replicated in the struggle to eliminate disease
• Reasons for the success of the smallpox eradication programme

  • The virus was stable-it did not mutate therefore its surface antigens did not change, therefore the same vaccine could be used worldwide which made it cheap to produce the vaccine
  • The vaccine was a 'live attenuated one, being produced from a harmless strain of a similar virus
  • The vaccine could be transported without becoming unviable, as it could be freeze-dried and kept at high temperatures for up to 6 months, thus it was suitable for the tropics
  • The symptoms made it easy to identify infected people (surveillance was possible)
  • Humans being the only reservoirs of infection and there were no carriers making it easier to break the transmission pathway
  • The consistency of the effort, vaccination, surveillance and containment of all outbreaks on a global scale