Vaccines (AQA AS Biology) : Revision Note

Vaccines

• Vaccines introduce pathogenic antigens into the body, triggering a specific immune response which results in the release of antibodies by plasma cells

  • Vaccines can contain:

    • weakened forms of the pathogen

    • antigens

    • genetic material that codes for the antigens

• Vaccinations produce active immunity, as they cause memory cells to be produced

  • The immune system recognises the antigen when the pathogen itself is encountered, and produces antibodies in a faster, stronger secondary immune response

  • The secondary response is large enough that the pathogen is eliminated before an individual experiences symptoms

Herd Immunity

• Vaccines provide protection for individuals and populations against disease

• Herd immunity occurs when a sufficiently large proportion of the population has been vaccinated

  • There are not enough susceptible individuals left in the population and the infection can no longer spread

• Those who are not immunised are protected by the high number of vaccinated individuals and are unlikely to contract an infection

  • This is very important for protection of individuals who are unable to be vaccinated, e.g. the very young and those with weak immune systems

• The proportion of the population that needs to be vaccinated in order to achieve herd immunity is different for each disease

  • The more infectious a disease, the higher the proportion that needs to be vaccinated

• If vaccination rates fall below the required level then herd immunity can break down

  • E.g. there was an outbreak of measles in Swansea in 2012 due to reduced vaccine uptake