Vaccinations (Edexcel IGCSE Biology): Revision Note

Vaccinations

• Vaccines are used to help the body develop immunity to infectious diseases

  • Vaccines have reduced the cases of certain diseases drastically or even eradicated some diseases worldwide

• A vaccine contains harmless versions of a pathogen

• Scientists ensure that vaccines contain harmless pathogens by:

  • Killing the pathogen

  • Using a weakened version of a pathogen (attenuated vaccine)

  • Using fragments of pathogens

• A vaccine may be administered orally, nasally or via an injection

How vaccines work

• Once in the bloodstream, the pathogen's antigens contained within the vaccine can trigger an immune response in the following way:

  • Lymphocytes recognise the antigens in the bloodstream

  • The activated lymphocytes produce antibodies specific to the antigen encountered

  • Memory cells are produced from the lymphocytes

  • Memory cells and antibodies subsequently remain circulating in the blood stream

The process of long-term immunity by vaccination

• Future infection by the same pathogen that an individual has been vaccinated against will trigger an immune response that is much faster and larger than the initial one.

• This is because vaccination leads to the production of memory cells (a type of long-lasting lymphocyte) that remain in the body for many years. If the vaccinated individual is later infected by the same pathogen, these memory cells produce antibodies more quickly and in greater quantities

• Because the response is so rapid, the pathogen is unable to cause disease, and the individual is said to be immune.

Graph showing the number of measles antibodies in the blood following vaccination. The immune response (production of antibodies) to the infection occurs much faster and is greater because of vaccination.