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Artificial passive immunity

When antibodies made in one individual are extracted and injected into another individual to protect them against a disease such as tetanus or rabies.

Artificial active immunity

The process by which the body produces antibodies to an antigen that it has been exposed to through immunisation.

Natural passive immunity

The process by which a mammalian mother passes antibodies to her baby through the placenta and in breast milk.

Natural active immunity

When a body is exposed to a live pathogen, develops antibodies to it and is in future immune to that disease as a result of the secondary immune response.

Herd immunity

If a high percentage of a population is immune to a disease the disease cannot be passed on because it cannot find new hosts.


The process of exposing individuals to inactivated antigens to allow them to develop active artificial immunity.


A communicable disease caused by bacteria. It affects millions of people around the world and can be cured by antibiotics, but increasingly the pathogenic bacteria are becoming resistant to the most widely used antibiotics.



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.


The first milk produced by the mammary glands which is particularly high in antibodies to protect the newborn mammal against disease.


Muscles or glands which bring about changes in response to a stimulus


The yellow liquid which supports all the cells of the blood and transports dissolved substances around the body


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


A poisonous or toxic substance produced by pathogens.


Vaccination uses the natural responses of the immune system to protect us against dangerous diseases. In the primary immune response antibodies to a pathogen are produced by the plasma cells produced from the B effector cells. The primary immune response is very effective but it can take days or even weeks to become fully active against a particular pathogen and in the meantime we get ill and suffer the symptoms of disease. If we meet the pathogen again, however, we have a secondary immune response which is much faster. B memory cells are formed at the same time as B effector cells. They are very long-lived and enable the body to respond very rapidly to a second invasion by the same antigen. So once we have experienced a pathogen, we have immunity against that disease in future.

More detailed information about the immune system is available here.

Different types of immunity

  • natural active immunity: when your body produces antibodies in response to exposure to a live pathogen, so that on a second exposure to the same pathogen you rapidly produce many antibodies and do not suffer the symptoms of disease.
  • Primary and secondary responses of the body to infection

    The primary and secondary responses of the body to infection

  • Photo of a woman breast feeding

    A mother gives her baby natural passive immunity through the placenta and her breast milk to help protect it against disease in the early months of life.
    (Photo credit: Aurimas Mikalauskas)

    natural passive immunity: when preformed antibodies pass from a mother to her foetus through the placenta during pregnancy, and to the newborn baby through breast milk, especially colostrum. This provides the baby with temporary immunity until its own system becomes active – the antibodies from the mother do not last long and are not replaced.
  • artificial active immunity: when small amounts of inactivated or attenuated antigen in a vaccine is used to produce immunity in a person.
  • artificial passive immunity: when antibodies formed in one individual are extracted and injected into another individual to protect them against a rapid-acting and dangerous pathogen. This does not confer long-term immunity, because the antibodies are gradually broken down and not replaced, but it can prevent fatal diseases such as rabies and tetanus.


Some diseases cause serious risk to individuals or populations. Rather than wait for people to become ill and then try to cure them, we can trigger the natural immune response artificially. We protect people from disease by exposing them to a vaccine. This is a pathogen that has been made non-infective without reducing its ability to act as an antigen. It may be a bacterial toxin with one or more chemical groups changed so it is no longer toxic. It may be inactivated viruses or dead bacteria or attenuated pathogens (viable but modified so they cannot cause disease). Increasingly, fragments of the outer coats of viruses and bacteria, or even DNA segments, are used as vaccines. The body produces antibodies and memory cells to the antigen and so is prepared with a rapid secondary response if it meets the live pathogen. Vaccination or immunisation is the procedure by which we produce active immunity in people through an artificial stimulus.

Immunisation protects individuals against potentially damaging or fatal diseases, but it is also used to eradicate, eliminate or control diseases that cause large numbers of deaths, disabilities or illnesses within a society.

Herd immunity

Herd immunity occurs when a significant proportion of the population is vaccinated against a disease. A disease can only be controlled or eliminated if enough people are vaccinated against it to make it almost impossible for the disease to spread. Herd immunity protects both the people who have been vaccinated against the disease and those people who for some reason have not been vaccinated.

Herd immunity

Herd immunity protects the very young, the very old and those affected by other diseases who cannot cope with vaccinations.

The percentage of the population that needs to be vaccinated to give herd immunity depends on factors such as how the disease is spread and how infectious it is.

Some diseases such as diphtheria, tetanus, polio, strains of meningitis and pertussis are so potentially serious that all children in the UK (and many other countries) are offered vaccines against them. This gives herd immunity to the whole population. For other diseases such as ‘flu, only vulnerable people are vaccinated as routine, but if there is a serious outbreak of disease the whole population is offered vaccination to provide herd immunity.

Bar chart showing different levels needed to achieve herd immunity for different diseases

Different diseases need different percentages of the population to be vaccinated to give herd immunity. The threshold values show a range because they depend on the size and overall health of the population being vaccinated.


Vaccination can play an important part in controlling and even eradicating endemic diseases. An endemic disease is one where the disease, or the pathogen, is always present in an environment (eg chicken pox in UK school children, tuberculosis in the Indian sub-continent and malaria in regions of Africa).

Smallpox is an example of a once deadly disease that no longer exists, thanks at least in part to vaccination. Polio is another disease, once endemic across the world, which now only exists in a tiny number of countries. Polio vaccination programmes are playing an important part in the control of this disease.

EITHER: Investigate the role of vaccines in the eradication of smallpox. Present your findings, making them accessible and interesting to the widest possible audience whilst retaining scientific rigour.

OR Investigate the attempts to rid the world of polio using vaccines. Present your findings, making them accessible and interesting to the widest possible audience whilst retaining scientific rigour.