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Glossary for terms related to vaccines

Glossary of terms related to vaccines and their role in preventing infectious diseases.




Active immunity

The production of antibodies against a specific disease by the immune system. Active immunity can be acquired in two ways, either by contracting the disease or through vaccination. Active immunity is usually long lasting, meaning an individual is often protected from the disease for the duration of their lives.


An adjuvant is an ingredient used in some vaccines that stimulates the immune system to improve the immune response to a vaccine. Alum is an example of an adjuvant used with vaccines. Vaccine antigens adsorb to alum and elute from it following injection into the host. Alum acts a mild irritant as well, bringing about leukocytes necessary for generation of an immune response.


A protein found in the blood that is produced in response to foreign substances (e.g. bacteria or viruses) invading the body. Antibodies protect the body from disease by binding to these organisms and destroying them.


Foreign substances (e.g. bacteria or viruses) in the body that are capable of causing disease. The presence of antigens in the body triggers an immune response, usually the production of antibodies.


A chemical substance that kills or inhibits the growth of microorganisms such as bacteria, viruses or fungi.

Antimicrobial Stewardship

An organisational or healthcare-system-wide approach to promoting and monitoring judicious use of antimicrobials to preserve their future effectiveness.


Literally “against-virus” — any medicine capable of destroying or weakening a virus.

Attenuated vaccine

A vaccine in which live virus is weakened through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. Attenuated vaccines currently licensed in the United States include measles, mumps, rubella, polio, yellow fever and varicella. Also known as a live vaccine. It generates an active immune response in the host by subsequent production of antibodies against the antigen.

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B cells

White blood cells that help the body defend itself against infection. These cells are produced in bone marrow and develop into plasma cells which produce antibodies. Also known as B lymphocytes.

Blood culture

A microbiological culture of blood, which usually is a sterile environment. It is employed to detect infections that are spreading through the bloodstream, mainly in patients with sepsis.

Booster doses

Additional doses of a vaccine needed periodically to “boost” the immune system. For example, the tetanus and diphtheria (Td) vaccine which is recommended for adults every ten years.

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That which can be transmitted from one person or animal to another. Also known as infectious.

Community immunity

See Herd Immunity

Conjugate vaccine

The joining together of two compounds (usually a protein and polysaccharide) to increase a vaccine’s effectiveness.

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A combination vaccine that provides immunity against three diseases – Diphtheria, Pertussis (Whooping Cough), and Tetanus. Its injection into a host stimulates production of antibodies against the pathogens Corynebacterium diphtheriae, Bordetella pertussis, and Clostridium tetani.

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The extent to which medical interventions achieve health improvements under ideal circumstances.


The continual, low-level presence of disease in a community


The occurrence of disease within a specific geographical area or population that is in excess of what is normally expected.


The study of factors that have an impact on disease in the human community. Often used in the control of health problems.


The complete and permanent worldwide reduction to zero new cases of an infectious disease through deliberate efforts; no further control measures are required.

Expanded Programme on Immunisations (EPI)

The EPI was established in 1974 to develop and expand immunisation programmes throughout the world. Problems encountered by the Programme have included: lack of public and governmental awareness of the scope and seriousness of the target diseases; ineffective programme management; inadequate equipment and skills for vaccine storage and handling; and insufficient means for monitoring programme impact as reflected by increasing immunisation coverage levels and decreasing incidence of the target diseases.

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Hepatitis A

A virus transmitted through ingestion of contaminated food or water.

Hepatitis B

A virus transmitted by infected blood or blood products, or through unprotected sex with someone who is infected.

Hepatitis C

A virus transmitted by infected blood or blood products, or through unprotected sex with someone who is infected.

Hepatitis D

A virus transmitted by infected blood or blood products, or through unprotected sex with someone who is infected.

Hepatitis E

A virus transmitted through ingestion of contaminated food or water.

Herd immunity

A situation in which a sufficient proportion of a population is immune to an infectious disease (through vaccination and/or prior illness) to make its spread from person to person unlikely. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the disease has little opportunity to spread within the community.

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Immune system

The complex system in the body responsible for fighting disease. Its primary function is to identify foreign substances in the body (bacteria, viruses, fungi or parasites) and develop a defence against them. This defence is known as the immune response. This includes production of protein molecules called antibodies to eliminate foreign organisms that invade the body.


Protection against a disease. There are two types of immunity, passive and active. See active and passive immunity.


The process by which a person or animal becomes protected against a disease. This term is often used interchangeably with vaccination or inoculation.


The changes in the immune system associated with age. Refers to the age-associated decline of the immune system that may contribute to the increased incidence and severity of infectious diseases and possibly certain cancers in the elderly.

Inactivated vaccine

A vaccine made from viruses and bacteria that have been killed through physical or chemical processes. These killed organisms cannot cause disease.


The number of new disease cases reported in a population over a certain period of time.


The invasion and reproduction of pathogenic (disease causing) organisms inside the body.


The measure of the ability of a pathogen to cause infection.

Infection Control

The processes of preventing the occurrence or spread or infection in healthcare settings.

Inflammatory Response

The body’s reaction to many infections, mediated by the immune system.

Influenza vaccine

Also known as flu shots or flu jabs, this is a vaccine that provide considerable immunity against influenza viruses which are the most common causative agents of flu.

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Live vaccine

A vaccine in which live virus is weakened (attenuated) through chemical or physical processes in order to produce an immune response without causing the severe effects of the disease. See Attenuated vaccines.


Cells that contribute to the immune response of the body. Originally produced in the bone marrow, the ones that remain and mature there are known as B-Lymphocytes and eventually become B cells. The ones that migrate to and mature in the thymus are known as T-lymphocytes and become T cells.

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A disease caused by a virus spread rapidly by droplet aerosolisation. It is marked by the eruption of red circular spots on the skin.


An infection of the protective membranes that surround the brain and spinal cord (meninges). It can be caused by bacteria (Neisseria meningitidis) or virus (Enteroviruses).

Meningococcal vaccine

A vaccine used to prevent infection by Neisseria meningitidis.


A combination vaccine that provides immunity against three diseases – Measles, Mumps, and Rubella. Its injection into a host stimulates production of antibodies against the pathogens Measles morbillivirus, Mumps rubulavirus, and Rubella virus.


A disease caused by an airborne virus and is highly contagious. It causes painful swelling of one or both parotid salivary glands.

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Opportunistic Pathogens

An infectious microorganism that is not normally associated with disease but that can cause illness when the host’s immune system is weakened.

Oral polio vaccine (OPV)

A preparation of live attenuated polio virus, used to immunize against polio and developed by Dr. Albert Sabin in 1961. OPV is administered orally (by mouth).

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An epidemic occurring over a very large geographic area.

Passive immunity

Protection against disease through antibodies produced by another human being or animal. Passive immunity is effective, but protection is generally limited and diminishes over time (usually a few weeks or months). For example, maternal antibodies are passed to the infant prior to birth. These antibodies temporarily protect the baby for the first 4-6 months of life.


A disease causing microorganism.


The ability of a pathogen to cause disease.

Pertussis (also known as whooping cough)

An infectious bacterial disease caused by Bordetella pertussis that produces violent, spasmodic coughing; also called whooping cough.

Pneumococcal vaccine

Vaccine against Streptococcus pneumoniae. It provides defence against diseases like pneumonia, meningitis, and sepsis.

Poliomyelitis (also known as polio)

An acute infectious viral disease characterized by fever, paralysis, and atrophy of skeletal muscles. The Global Polio Eradication Initiative was launched in 1988 with the goal of eradicating polio from the earth through routine and mass polio vaccination programs.

Polysaccharide vaccine

A vaccine that is composed of long chains of sugar molecules that resemble the surface of certain types of bacteria. Polysaccharide vaccines are available for pneumococcal disease, meningococcal disease, and Hib.


A measure of strength.


The number of disease cases (new and existing) within a population over a given time period.

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The isolation of a person or animal who has a disease (or is suspected of having a disease) in order to prevent further spread of the disease.

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A property of some microorganisms which renders certain antimicrobials ineffective against them. Resistance may be an intrinsic characteristic of a microorganism or may be acquired and selected by exposure to antimicrobials.


A disease best known by its distinctive red rash. It is caused by Rubella virus, and is similar in its manifestation to measles. However, rubella isn’t as severe or as contagious.

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A highly infectious, often fatal disease caused by a poxvirus and characterized by high fever and aches with subsequent widespread eruption of pimples that blister, produce pus, and form pockmarks. Also called variola.


A group of microorganisms within a species with the most similar morphological and cultural characteristics.


Surveillance of antimicrobial resistance is the tracking of changes in microbial populations.

Systemic Infections

An infection which has spread to multiple parts of the body.

Systematic Review

A review in which evidence from scientific publications has been identified, appraised and synthesised in a methodical way according to predetermined criteria.

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Tuberculosis (TB)

A disease caused by the bacterium Mycobacterium tuberculosis. The bacteria usually attack the lungs; however, TB bacteria can attack any part of the body such as the kidney, spine, and brain. If not treated properly, TB disease can be fatal.

Tuberculosis vaccine (Bacillus Calmette-Guérin, BCG vaccine)

A vaccine against tuberculosis that is prepared from a strain of the live attenuated bovine tuberculosis bacillus. Tuberculosis vaccine is used in many countries with a high prevalence of tuberculosis to prevent childhood tuberculous meningitis and miliary disease. It is administered intradermally and often leaves a scar.

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Injection of a killed or weakened infectious organism in order to prevent the disease. See Immunisation.


A substance when introduced into a host, stimulates the body to produce antibodies, subsequently increasing the host’s immunity. Vaccines are administered through needle injections, by mouth and by aerosol.

Vaccine-preventable diseases

Diseases for which vaccines exist that can confer partial or complete protection.


Also called chickenpox, it is a very contagious disease caused by the varicella-zoster virus (VZV). It causes a blister-like rash, itching, tiredness, and fever.

Varicella vaccine

The vaccine is a preventive measure against varicella or chickenpox. It is made from a live and attenuated virus.


The relative capacity of a pathogen to overcome its host’s defences.


A tiny organism that multiplies within cells and causes disease such as chickenpox, measles, mumps, rubella, and hepatitis. Viruses are not affected by antibiotics, the drugs used to kill bacteria.

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The Role of Vaccines in Preventing Infectious Diseases and Antimicrobial Resistance

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