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Immune system

The body's natural defence mechanism against infectious diseases.

Vaccination

A small amount of dead or weakened pathogen is introduced into the body. It prepares the immune system to prevent future infections with the live pathogen.

Antibody

Proteins produced by the plasma cells (B cells, a type of white blood cell) of the immune system in response to a specific antigen..

Vaccine

Medicine that contains a dead or weakened pathogen. It stimulates the immune system so that the vaccinated person has an immunity against that particular disease.

Polio

Viral disease causing paralysis which has been eradicated from most countries in the world by a vaccination programme

1796: Vaccination

Smallpox was a killer disease in the 18th century. Infected people would become covered in horrible skin sores and often die a painful death. Those who recovered were left with terrible scars or poc marks on their skin. We now understand that it is caused by a virus (the variola virus). It infects the internal organs, causes severe blistering of the skin and death due to blood poisoning or secondary infections.

Kill or cure

Edward Jenner is credited with the development of vaccination but in fact it was first introduced into England by Lady Mary Wortley Montagu in 1721. She tried a method that was used in Turkey where people deliberately infected themselves with a mild form of smallpox. This was the first form of inoculation. Sadly, many people died from the smallpox they were using to protect themselves. Clearly something different needed to be done.

Observation and vaccination

Jenner was a doctor who worked in Gloucestershire and the great advance he made was to notice that individuals who had contracted cowpox (the cow's equivalent of smallpox) rarely caught the deadly human version. In 1796 he deliberately infected an eight year old boy called James Phipps with the pus from a cowpox sore. The boy became ill with cowpox but recovered. He then infected him with the normally deadly smallpox. As Jenner had predicted the earlier infection with the cowpox actually protected the boy who never caught smallpox. The practice of modern vaccination was born.

A painting showing Jenner vaccinating James Phipps
(Wellcome Images)
Lancets (knives) used by Jenner for vaccinations
(Wellcome Images)

Cowpox vs smallpox

After many more successful vaccinations, Jenner published his results in 1798. However, they were met with scepticism and many doctors still carried out the more dangerous practice of inoculation with live smallpox pus. It was not until 1840 that this dangerous practice was banned and in 1853 vaccination by Jenner's method was made compulsory. Protestors argued against compulsory vaccination, saying that it limited their personal choice; a similar debate to the one that raged around 2000 over the MMR vaccine.

Jenner’s original paper ‘An inquiry into the natural history of a disease known in Glostershire under the name of Cow-Pox’
(Wellcome Images)

Understanding the immune system

When Jenner tried his first vaccinations, the way microbes cause infectious diseases was not understood and he did not know about the immune system. We now understand how vaccination works.

Pathogens are microbes that cause disease. These can be viruses, like smallpox, or bacteria. If a small amount of the weakened, or inactive microbe is introduced into the body it stimulates the immune system to produce antibodies to fight off the disease. The immune system remembers the microbe and can defend the body against any live form of the microbe that it may encounter in the future. The person is said to be immune to the disease.

Find out more about vaccination and immune memory.

Eradication of smallpox

Nearly 300 years after Jenner's discovery, a programme of vaccination by the World Health Organisation (WHO) was started with the aim to completely eradicate the smallpox virus. It is estimated that smallpox killed 500 million people worldwide during the last century. The last case of naturally-transmitted smallpox was reported in Africa, in 1977. In 1980, the WHO officially announced the end of smallpox. There remain two highly-guarded stocks of the virus which are preserved for research purposes.

Smallpox pustules on a person’s leg
A clump of smallpox viruses viewed using an electron microscope. Over 13 million of these viruses would fit onto a full stop on this page
(CDC/ Fred Murphy)

Jenner's discovery has led to a greater understanding of the human immune system and vaccination programmes against diseases such as measles, mumps, polio and tuberculosis have improved the health of millions who need not fear these killer diseases.

Question

a) We call the process of introducing a small amount of harmless pathogen 'vaccination'. Why do we call it this?

Edward Jenner's first trial used the pus from a cowpox sore. The Latin for cow is vacca so the new word was vacca-nation.

b) How many people died of smallpox in the last century?

500 million

c) Briefly describe how immunisation works.

The immune system produces antibodies to fight the pathogen in the vaccination. These antibodies stay in the immune system and are quickly ready to fight the harmful pathogen should it invade the body. Because the body is prepared with antibodies already, it can fight the disease more effectively.