People can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens.
Vaccination involves putting a small amount of an inactive or weakened form of a pathogen into the body. Vaccines can contain:
- dead pathogens
- live pathogens treated to make them harmless
- harmless fragments of the pathogen
- toxins produced by pathogens.
These all act as antigens. When injected into the body, they stimulate white blood cells to produce antibodies against the pathogen.
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Because the vaccine contains only a weakened or harmless version of a pathogen, the vaccinated person is not in danger of developing disease (although some people may suffer a mild reaction). If the person does get infected by the pathogen later, the required lymphocytes are able to reproduce rapidly and destroy it.
Vaccines and boosters
Vaccines in early childhood can give protection against many serious diseases. Sometimes more than one vaccine is given at a time, like the MMR triple vaccine against mumps, measles and rubella.
Sometimes vaccine boosters are needed, because the immune response “memory” weakens over time. Anti-tetanus injections may need to be repeated every ten years.
Mutations of bacteria and viruses
Some bacteria and viruses mutate very quickly. This means
that vaccines developed to protect against these pathogens no longer work
so effectively. When this happens, an epidemic occurs where lots of people
become infected and ill - and often die. An recent example is bird flu.
A new vaccine has to be developed to protect against these new forms of
pathogen.
[ This page has been adapted from www.bbc.co.uk/schools/gcsebitesize/science
]