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Defending against infection

Protecting against pathogens


Vaccination causes the body to produce enough white blood cells to protect itself against a pathogen. Antibiotics are effective against bacteria, but not against viruses. Some strains of bacteria are resistant to antibiotics. So people can be immunised against a pathogen through vaccination. Different vaccines are needed for different pathogens. For example, the MMR vaccine is used to protect children against measles, mumps and rubella (German measles).

Vaccination involves putting a small amount of an inactive form of a pathogen, or dead pathogen, into the body.

Vaccines can contain:

  • live pathogens treated to make them harmless
  • harmless fragments of the pathogen
  • dead pathogens.

These all act as antigens. When injected into the body, they stimulate white blood cells to produce antibodies against the pathogen. If the person does get infected by the pathogen later, their body can respond in the same way as if they had had the disease before. If a large proportion of the population is immune to a particular pathogen, the spread of that pathogen is greatly reduced.


One simple way to reduce the risk of infection is to maintain personal hygiene and to keep hospitals clean. In the 19th century, Ignaz Semmelweiss realised the importance of cleanliness in hospitals. Semmelweiss insisted that doctors should wash their hands before examining patients, something that was not common at the time. This policy greatly reduced the number of deaths from infectious diseases in his hospital. Unfortunately, although his ideas were successful, they were ignored at the time because people did not know that diseases were caused by pathogens that could be killed.

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