Immunisation is the process of introducing material into a host in order to elicit a protective response by the immune system. The material used in the vaccine is typically derived from a pathogenic microorganism that is modified in some way so that it does not cause disease. This material contains antigens (i.e. molecules recognised by lymphocytes). After immunisation, the T and B lymphocytes capable of recognising the material in the vaccine become activated, differentiate into effector cells and act to remove the antigens from the body. Activated B cells begin to produce antibody and eventually become long‐lived memory B cells that migrate to the bone marrow and continue to secrete antibody. Activated T cells recognise and destroy infected cells and can also develop into long‐lived memory T cells. On subsequent exposure to the same pathogen (and antigens), the memory response is quicker and far stronger than a primary response. It is this memory response that protects the host from disease.

Key Concepts

  • Vaccines have saved more lives than any other medical invention.
  • Vaccines simulate a real infection so that the immune system can develop a protective response against a specific pathogen.
  • Vaccination provides long‐lived immunologic memory so that the immune response during a subsequent exposure to a pathogen is more rapid and much stronger.
  • Protective immunity is a complex process that differs for each pathogen.
  • While orders of magnitude safer than the diseases they prevent, vaccines may cause side effects.

Keywords: immunisation; vaccination; vaccines; adjuvants; antigen; immune response; humoral immunity; antibodies; cellular immunity

Figure 1. Overview of vaccination. Disease‐causing microorganisms are combined with adjuvants (immunostimulatory compounds) and injected into healthy individuals in order to provoke an immune response. The vaccine elicits pathogen‐specific immunity through the development of long‐lived memory cells (B cells producing antibodies and T cells capable of destroying infected cells). These memory cells are primed to immediately respond when the vaccine recipient encounters the pathogen again. The response to this subsequent exposure is typically so strong that the pathogen is eliminated before infection and clinical disease can occur.


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Further Reading

NIAID (2012) The Jordan Report: Accelerated Development of Vaccines 2012. US Department of Health and Human Services, National Institutes of Health, National Institute of Allergy, Immunology, and Infectious Diseases.

Owen JA, Punt J and Stranford SA (2013) Kuby Immunology, 7th edn. New York: W.H. Freeman and Company.

Paul WE (2013) Fundamental Immunology, 7th edn. Philadelphia, PA: Lippincott Williams and Wilkins.

Plotkin SL and Orenstein WA (2017) Vaccines, 7th edn. China: Elsevier Saunders.

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Kennedy, Richard(Apr 2018) Vaccination. In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1002/9780470015902.a0000489.pub3]