ADJUVANT

A substance which, when given at the same time as an antigen, increases the immune response to the antigen. Adjuvants are most commonly derived from minerals, oily materials or derivatives of certain micro-organisms.

ANTIBODIES

Proteins found in blood plasma (immunoglobulins) which play a part in the body's defence mechanisms against micro-organisms due to their ability to react specifically with an antigen. Antibody production is carried out by the cells of the immune system and is stimulated by the corresponding antigen.

ANTIGEN

A chemical substance with the ability to stimulate the body to produce an antibody which will react specifically with that antigen.

ANTIGENICITY

The ability of antigens to stimulate antibody production or in more general terms, to provoke a specific immunological response.

ASYMPTOMATIC

Without clinical signs or symptoms of the disease.

BACTERIUM/BACTERIA

A very common single cell micro-organism which is very small and typically around one micron in diameter. Individual cells may be spherical, straight or curved rods, or spirals. They may have capsules or they may have whip-like appendages (flagella) which help them to move. Some bacteria cause disease in man or animals (pathogenic), while others are harmless (non-pathogenic) and exist in man where they help many of the body's processes such as digestion in the gut.

BOOSTER INJECTION

A technique commonly used in vaccination in which the vaccine is re-administered after a given (and variable) time (weeks, months or years) in order to reinforce or restore immunity.

CONTRA-INDICATION

Any reason why an individual should not receive a particular treatment.

CONJUGATE VACCINE

Vaccines utilising purified carbohydrates (polysaccharides) from a bacterial capsule linked to protein carriers to improve the immune stimulatory effect.

ENDEMIC

Constant or periodic occurrence of a disease in a population.

EPIDEMIC

Simultaneous occurrence of a disease during a limited time in a large number of people in the same geographic region.

EPIDEMIOLOGY

The scientific study of the distribution of diseases.

IMMUNISATION

The acquisition of natural immunity or immunity due to vaccination (active immunisation) or by the injection of immunoglobulins (passive immunisation).

IMMUNITY

A state of relative resistance to an infection which may be innate (from inherited qualities) or acquired actively or passively, naturally or artificially. Active immunity is acquired either through a natural infection or through vaccination while passive immunity is acquired either naturally from the transfer of maternal antibodies to the child or artificially by the injection of immunoglobulin.

IMMUNOSUPRESSION OR IMMUNODEFICIENCY

Conditions caused by disease or drugs in which the normal immune response to an antigen is diminished.

IMMUNOGEN

An alternative term often applied to an antigen.

IMMUNOGLOBULINS

Any of the structurally related glycoproteins that function as antibodies.

INFECTION

The presence in the body of a foreign organism (bacterium, virus, fungus or parasite) capable of multiplying and causing damage. The infection may be accompanied by symptoms and signs or it may be asymptomatic.

INFLAMMATION

The result of the release of body chemicals at a site of tissue damage. There are normally four main symptoms of inflammation - heat, pain, redness and swelling. The injury leading to inflammation may be caused by chemicals, physical injury, bacterial, viral, fungal or parasitic infection or by an antigenic reaction.

INOCULATION

The introduction of a disease agent, e.g. vaccine virus, into a healthy individual to produce a mild form of the disease followed by immunity.

INTRADERMAL INJECTION

An injection which is given into the uppermost layer of the skin (the dermis).

INTRAMUSCULAR INJECTION

An injection given into the muscle tissue, usually in the upper arm but occasionally in the thigh or buttock.

MICRO-ORGANISM

A very small organism which can only be seen with a microscope or an electron microscope. Under the generic term 'micro-organisms' one finds bacteria, viruses, microscopic fungi, protozoa and some parasites.

PANDEMIC

An epidemic happening on several continents at the same time.

PARASITE

An organism which is obliged to obtain its food by living off the cells of another living organism.

PATHOGEN

A disease producing agent.

PREVALENCE

The number of patients with a given condition at a given time as a mathematical function of the population.

SEROCONVERSION

The term applied to the development of antibodies in a subject whose blood did not previously contain these antibodies following the introduction of an antigen into the body. Before seroconversion the subject is said to be seronegative - after seroconversion the subject is seropositive.

SPORADIC (CASES)

Infections which occur in small numbers, in isolated cases and separated by time without a strong epidemiological link.

SUBCUTANEOUS INJECTION

An injection given below the upper layer of the skin but deeper than intra-dermal.

VACCINE

A vaccine is a non-pathogenic preparation of an antigen which following its introduction into the body stimulates the development of a protective immune response in the recipient such that he/she develops specific antibodies to the antigen introduced. This means that the individual is able to fight the pathogenic disease if and when it occurs. Vaccines are differentiated into the following categories:

Live Vaccines

These contain a strain of the bacterium or the virus very close to the wild strain which has lost its ability to cause disease (attenuated) but which is capable of growing in the body and in doing so it stimulates an immune response.

Inactivated or Killed Vaccines

These contain inactivated bacteria or viruses which are incapable of growing in the body but whose presence stimulates a protective immune response to future challenge with the live micro-organism. Some inactivated vaccines only contain fragments of the micro-organism or modified chemical substance produced by the micro-organism.

VACCINE ASSOCIATION

The simultaneous administration of several vaccines in different sites at the same time.

VACCINE CALENDAR

The vaccine calendar in the UK for childhood immunisations is drawn up by the Joint Committee on Vaccination and Immunisation (JCVI). It lists the vaccines which are recommended for children from birth onwards with the recommended time that they should be administered and the number of doses required. In their recommendations, the JCVI take into account the prevailing epidemiology of the diseases in the UK, the vaccine calendars of other countries and the recommendations of the World Health Organisation (WHO).

VACCINE COMBINATION

A vaccine which contains several antigens within the same injection (e.g. DTP, DTP-Hib, DT, which contain combinations of diphtheria, tetanus, whooping cough and Haemophilus influenzae Type b vaccines all in one syringe and administered at the same time).

VALENCE

Within the scope of combination vaccines the valence of the vaccine is the number of different vaccines which are included in the preparation e.g. DTP vaccine is said to be trivalent.

VIRUS

Viruses are very small, significantly smaller than a bacteria. Unlike bacteria, viruses are incapable of living and reproducing outside the host cell. A virus is referred to as an obligate parasite. Each virus particle is a mixture of proteins forming a coat which surrounds a core of DNA or RNA, the material which instructs the host cell to make more viruses.