What exactly does meningitis "control" mean? Why are we talking about elimination of the disease, and not eradication? The glossary below provides answers to these questions and will help you better understand the terms that are used on this website.

Main source: The US Centers for Disease Control and Prevention.


Acute: Sudden, intense, and short-termed.

Agent: A factor, such as a microorganism or a chemical substance whose presence, excessive presence, or (in deficiency diseases) relative absence is essential for the occurrence of a disease.

Antibiotic: A substance that fights bacteria.

Antibody: 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.

Antigen: 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.

Applied epidemiology: The application/practice of epidemiology to address public health issues.

Attack rate: A variant of an incident rate, applied to a narrowly defined population observed for a limited period of time, such as during an epidemic.

Attenuated: An attenuated vaccine is one that has been weakened by chemicals or other processes so that it will produce an adequate immune response without causing the serious effects of an infection.

Bacteria: (Plural for bacterium). Tiny microorganisms that reproduce by cell division and usually have a cell wall. Bacteria can be shaped like a sphere, rod, or spiral and can be found in virtually any environment.

Bivalent vaccine: A vaccine that contains two antigens.

Booster: Administration of an additional vaccination to help increase or speed the immune response to a previous vaccination.

Coccus: Type of bacterium.

Cohort: A well-defined group of people who have had a common experience or exposure, who are then followed up for the incidence of new diseases or events, as in a cohort or prospective study. A group of people born during a particular period or year is called a birth cohort.

Combination vaccine: A combination of two or more vaccines (i.e., the diphtheria/tetanus/pertussis vaccine). Like the individual vaccines, combination vaccines are developed through scientific research. They are also tested through clinical trials for appropriateness, safety, and effectiveness before they are licensed and released for use by the public.

Conjugate vaccine: A vaccine in which a polysaccharide antigen is chemically joined with a protein molecule to improve the immunogenicity of the polysaccharide.

Contact: Exposure to a source of an infection, or a person so exposed.

Contagious: Capable of being transmitted from one person to another by contact or close proximity.

Control: Reduction of disease incidence, prevalence, morbidity, or mortality to a locally acceptable level as a result of deliberate effort.

Descriptive epidemiology: The aspect of epidemiology concerned with organizing and summarizing health-related data according to time, place, and person.

Distribution: In epidemiology, the frequency and pattern of health-related characteristics and events in a population.

DTPw vaccine: Trivalent vaccine for diphtheria–tetanus–whole cell pertussis.

Efficacy: In vaccine research, the ability of a vaccine to produce a desired clinical effect, such as protection against a specific infection or disease in a given population. A vaccine may be tested for efficacy in Phase 3 trials if it shows some promise in smaller Phase 1 and 2 trials.

Elimination: Reduction to zero of incidence of infection (or disease) caused by a specific agent in a defined geographical area as a result of deliberate efforts.

Endemic: The constant presence of a disease or infectious agent within a given geographic area or population group.

Environmental factor: An extrinsic factor (geology, climate, insects, sanitation, health services, etc.) that affects the agent and the opportunity for exposure.

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

Epidemiology: The study of the frequency and distribution of disease in human populations.

Epilepsy: A disorder of the central nervous system characterized by loss of consciousness and convulsions.

Eradication: Permanent reduction to zero of the worldwide incidence of infection caused by a specific agent as a result of deliberate efforts.

Etiology: Origin or cause.

Expanded Program on Immunization (EPI): Global effort of governments, WHO, UNICEF, other United Nations agencies, bilateral development agencies, and nongovernmental organizations to immunize the world's children against six vaccine-preventable diseases. They are: measles, diphtheria, whooping cough, tetanus, tuberculosis, and poliomyelitis.

Exposure: Contact with infectious agents (e.g., bacteria, parasite, and virus) in a manner that promotes transmission and increases the likelihood of disease.

Extinction: The specific infectious agent no longer exists in nature or in the laboratory.

Field test: A test that is conducted in a natural environment and under natural conditions.

Heptavalent vaccine: A vaccine that contains seven antigens.

Hib disease: Disease caused by Haemophilus influenzae type b. Until recently, this disease was the most common cause of deadly bacterial meningitis in children. It can also cause infection of the bloodstream, pneumonia, epiglottis, and otitis media.

High-risk group: A group in the community with an elevated risk of disease.

Host factor: An intrinsic factor (age, race, sex, behavior, etc.) that influences an individual's exposure, susceptibility, or response to a causative agent.

Immune: A state of being protected against infectious diseases by either specific or non-specific mechanisms (i.e., immunization, previous natural infection, inoculation, or transfer of protective antibodies). For certain diseases, immune mothers may temporarily transfer protective antibodies to their newborns through the placenta. Protection can result from this placental transfer for up to 4–6 months.

Immune complex: The result of a reaction between an antigen and a specific antibody. This combination of antigen bound by antibody may or may not cause adverse effects in a person.

Immune response: The reaction of the immune system to foreign substances.

Immune system: The body’s very complex system (made of many organs and cells) that defends the body against infection, disease, and foreign substances.

Immunity: Protection against a disease. There are two types of immunity: passive and active. Immunity is indicated by the presence of antibodies in the blood and can be determined with a laboratory test. See active and passive immunity.

Immunity, active: 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 permanent, which means that an individual is protected from the disease for the duration of his or her life.

Immunity, herd: The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of individual members of the group. The resistance is a product of the number susceptible and the probability that those who are susceptible will come into contact with an infected person.

Immunity, passive: 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.

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

Immunogen: A substance capable of provoking an immune response. Also called an antigen.

Immunogenicity: The ability of an antigen or vaccine to stimulate immune responses.

Immunology: Branch of biology that studies immune reactions.

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

Incubation period: A period of subclinical or inapparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease.

Infectious: Capable of spreading disease. Also known as communicable.

Infectious agents: Organisms capable of spreading disease (e.g., bacteria or viruses).

Live 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.

Long-term memory: The ability that the immune system has to retain memory of the foreign protein and mount an immune response whenever challenged. Some vaccines (e.g., tetanus) are better at inducing or developing long-term memory than others are (e.g., flu or existing meningitis vaccines).

Lumbar puncture: A diagnostic test in which a small amount of cerebrospinal fluid (the fluid that surrounds the brain and spinal cord) is extracted for examination. Also called a spinal tap.

Lyophilization: Method of preserving perishable foodstuffs and chemical substances. Also known as freeze-drying.

Microbiology: A branch of biology dealing especially with microscopic forms of life (viruses, bacteria, etc.).

Monovalent vaccine: A vaccine that contains only one antigen.

Morbidity: Any departure, subjective or objective, from a state of physiological or psychological well-being.

Nasopharyngeal: Relating to the nose and pharynx or the nasopharynx.

Nasopharynx: Part of the pharynx that is located above the soft palate.

Outbreak: See epidemic.

Pathogen: An organism (e.g., bacterium, virus, parasite, and fungus) that causes disease in human beings.

Phase 1 (vaccine) clinical trial: A clinical trial of a vaccine conducted in a small number of healthy volunteers. A Phase 1 trial is designed to determine the vaccine’s safety and immunogenicity in humans, its metabolism and pharmacologic actions, and side effects associated with increasing doses.

Phase 2 (vaccine) clinical trial: Controlled clinical study of a vaccine to identify common short-term side effects and risks associated with the vaccine, to collect additional information on its immunogenicity, and to collect initial information on efficacy. Phase 2 trials enroll some subjects who have the same characteristics as persons who would be enrolled in an efficacy (Phase 3) trial of a vaccine. Phase 2 trials enroll up to several hundred participants.

Phase 3 (vaccine) clinical trial: Large controlled study to determine the ability of a vaccine to produce a desired clinical effect on the risk of a given infection, disease, or other clinical condition at an optimally selected dose and schedule. These trials also gather additional information about safety needed to evaluate the overall benefit-risk relationship of the vaccine. Phase 3 trials usually include several hundred to several thousand subjects.

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 Haemophilus influenzae type b.

Polyvalent vaccine: A vaccine that contains several antigens.

Protein: A type of organic compound that is one of the major components of cells and tissues.

Protocol: The detailed plan for a clinical trial that states the trial's rationale, purpose, routes of administration, length of study, eligibility criteria, and other aspects of trial design.

Purpuric (rash): Rash that is of a dark red color.

Quadrivalent vaccine: A vaccine that contains four antigens.

Risk: The probability that an event will occur; for example, that an individual will become ill or die within a stated period of time or age.

Risk factor: An aspect of personal behavior or lifestyle, an environmental exposure, or an inborn or inherited characteristic that is associated with an increased occurrence of disease or other health-related event.

Sensorineural deafness: Deafness caused by a lesion of sensorial organs.

Septicaemia: Severe infection caused by the development and dissemination of pathogen microorganisms in the blood.

Spinal tap: See lumbar puncture.

Strain: A biologic characteristic of a microorganism (i.e., bacterium or virus). The identity of a strain is defined by its genetic makeup, or code; changing just one piece of the code produces a new strain.

Surveillance: The systematic collection, analysis, interpretation, and dissemination of health data on an ongoing basis, to gain knowledge of the pattern of disease occurrence and potential in a community, in order to control and prevent disease in the community.

Titer: The quantity of a substance required to produce a reaction with a given volume of another substance. Or the detection of antibodies in blood through a laboratory test.

Toxoid: Inactivated or killed toxin (such as diphtheria or tetanus) used in vaccine production. A toxoid vaccine is made from a toxin (poison) that has been made harmless. A diphtheria toxoid vaccine immunizes against diphtheria; a tetanus toxoid vaccine immunizes against tetanus.

Trivalent vaccine: A vaccine that contains three antigens.

Vaccine: A product of weakened or killed microorganism (bacterium or virus) that stimulates an immune response that can prevent an infection or create resistance to an infection.

Virus: A microorganism that grows and reproduces in living cells. Vaccines prevent illnesses caused by the following viruses: hepatitis B, polio, measles, mumps, rubella, varicella, hepatitis A, etc.