How do vaccines work?

When we catch a disease naturally, we usually produce antibodies to the organism that causes it. Antibodies are proteins in the blood which remember the organism which caused the disease, can recognise it and inactivate it when we come into contact with it again. Without us actually experiencing the disease, vaccines teach our body’s immune system to produce antibodies and identify certain potentially infective organisms even though we have never come into contact with them.

Vaccines take various forms:

• Killed or inactivated vaccines are produced by chemically killing or inactivating bacteria or viruses. The now harmless bacteria or viruses, when injected, stimulate the body to produce antibodies, without the individual having to suffer the disease.
• Live vaccines are produced by weakening the ability of the organism to produce disease while retaining its ability to produce immunity.
• Vaccines may be made by identifying and purifying those fragments of the disease-producing organisms that are most import in stimulating antibodies. These fragments may be substances found on the surface of the organism which the immune system recognises or others such as the toxins produced by some bacteria.
• These fragments can also be produced by modifying the genetic material of a totally different cell so that this cell produces copies of these fragments, which can then be purified and used to make a vaccine.

Before any vaccine is used routinely, it must be studied in extensive clinical trials to make sure that it works and that it is safe to use. Rigorous trials of all vaccines, including routine childhood vaccines, have shown that they are highly effective and well tolerated. Trials are carried out by the manufacturers at every stage of development, and by independent UK scientific agencies such as the Public Health Laboratory Service Vaccine Evaluation Group. Following the introduction of a vaccine, surveillance continues through national reporting systems and groups such as the Immunisation Division of the Communicable Disease Surveillance Centre.

The Medicines Control Agency (MCA) in the UK or the European Medicines Evaluation Agency (EMEA) must be satisfied as to the quality, safety and efficacy of every vaccine before a marketing authorisation is issued. In addition, the quality of every batch of every vaccine used in the UK is checked by independent organisations such as the National Institute for Biological Standards and Control (NIBSC) or by other recognised European bodies.