Acellular vaccine: A vaccine containing partial cellular material as opposed to complete cells.
Acquired Immune Deficiency Syndrome (AIDS): A medical condition where the immune system cannot function properly in protecting the body from disease. As a result, the body cannot defend itself against common infections. AIDS is caused by the Human Immunodeficiency Virus (HIV).
Active immunity: The production of antibodies against a specific disease by the immune system either by contracting the disease or through vaccination.
Acute: A short-term, intense health effect.
Acute flaccid paralysis (AFP): Loss of muscle tone and decrease or absence of tendon reflexes in limbs, for example, due to polio
Adjuvant: A substance that is added to a vaccine during production to increase the body's immune response following vaccination.
Adverse events: Undesirable experiences occurring after vaccination that may or may not be related to the vaccine.
Advisory Committee on Immunisation Practices (ACIP): A panel of experts who make recommendations on the use of vaccines in the United States.
Allergy: A condition in which the body has an exaggerated response to a substance such as food or drug or pollen. Also known as hypersensitivity.
Anaphylaxis: An immediate and severe allergic reaction to a substance (e.g. food or drugs). Symptoms of anaphylaxis include breathing difficulties, loss of consciousness and a drop in blood pressure. This condition can be fatal and requires immediate medical attention.
Anthrax: An acute infectious disease caused by the spore-forming bacterium Bacillus anthracis. Anthrax occurs in hoofed mammals and can infect humans.
Antibiotic: A substance that fights bacteria.
Antibody: An immunological substance or protein found in the blood that is produced in response to foreign substances invading the body.
Antigens: Foreign substances in the body that are capable of causing disease. Antigens provoke an immune response, such as production of antibodies, cytokines, chemokines etc.
Antigenic drift: Minor change in genetic material of microorganisms that modifies their antigenicity. Antigenic drift occurs naturally and more rapidly in RNA viruses (e.g. influenza or HIV viruses).
Antigenic shift: Mutation in the genetic material of microorganisms such as viruses, resulting in novel strains. Antigenic shift in influenza viruses can be associated with human pandemics, in population immunologically naïve to the new strain.
Antitoxin: Antibodies capable of neutralising or destroying toxins generated by microorganisms including viruses and bacteria.
Antiviral: Compounds capable of destroying or weakening a virus.
Arthralgia: Joint pains.
Arthritis: Inflammation of the joints which results in pain and difficulty in movements.
Association: The degree to which the occurrence of two events is linked.
Asthma: A condition where the bronchial tubes in the lungs become easily irritable resulting to constriction of the airways and wheezing, coughing, difficulty in breathing and production of thick mucus.
Asymptomatic infection: The presence of an infection without visible symptoms. Also known as inapparent or subclinical infection.
Autism: A chronic developmental disorder usually diagnosed between 18 and 30 months of age. Symptoms include problems with social interaction and communication as well as repetitive interests and activities.
Bias: Systematic errors in the collection, analysis or interpretation of research data that lead to incorrect conclusions.
Biological plausibility: A causal association (or relationship between two factors) is consistent with existing medical knowledge.
Booster shots: Additional doses of a vaccine needed periodically to enhance the immune system. For example, the tetanus and diphtheria (Td) vaccine which is recommended for adults every ten years.
Brachial neuritis: Inflammation of nerves in the arm causing muscle weakness and pain.
Clinical trial: Before a drug or medication is licensed it has to be tested for safety and efficacy (to see whether it produces the desired protection) on smaller groups of humans. This is called clinical testing or research.
Combination vaccine: Two or more vaccines administered in a single dose in order to reduce the number of shots given.
Commensal bacteria: Bacteria that are natural inhabitants of the human body.
Communicable disease or infections: That which can be transmitted from one person or animal to another.
Community or 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.
Complement: A group of serum proteins involved in the control of inflammation, the activation of phagocytes and the lytic attack on cell membranes. The system can be activated by interaction with the immune system.
Conjugate vaccine: The joining together of two compounds (usually a protein and polysaccharide) to increase a vaccine's effectiveness.
Contact immunity: Secondary immunisation of contacts through the (protective) shedding of vaccine strains in stools.
Convulsion/seizure: The sudden onset of a jerking and staring spell usually caused by fever.
Deltoid: A muscle in the upper arm where vaccine shots are usually given.
Encephalitis: Inflammation of the brain that can result in permanent brain damage or death.
Epidemic: The occurrence of disease within a specific geographical area or population that is in excess of what is normally expected.
Endemic: The continual, presence of a disease in a community
Etiology: The cause of.
Exposure: Contact with infectious agents in a manner that may result to transmission and increases the likelihood of getting the disease.
Febrile: Relating to fever; feverish.
Guillain-Barre Syndrome (GBS): A rare neurological disease characterized by loss of reflexes and temporary paralysis.
Hives: An allergic condition that manifests by the eruption of red marks on the skin that are usually accompanied by itching. Also known as uticaria.
Hypersensitivity: A condition in which the body has an exaggerated response to a substance (e.g. food or drug). Also known as an allergy.
Hyposensitivity: A condition in which the body has a weakened or delayed reaction to a substance.
Immunoglobulin: A protein found in the blood that fights infection. Also known as gamma globulin.
Immune system: The complex system in the body responsible for fighting disease-causing organisms.
Immunity: Protection against a disease.
Immunogenicity: Capacity of a vaccine to induce an immune response.
Immunisation: The process by which a person or animal becomes protected against a disease. This term is often used interchangeably with vaccination or inoculation.
Immunosupression: When the immune system is weakened and unable to protect the body from disease.
Incidence: The number of new disease cases reported in a population over a certain period of time.
Incubation period: The time from contact with infectious agents to onset of disease.
Infectious agents: Organisms capable of spreading disease
Inflammation: Redness, swelling, heat and pain resulting from injury to tissue (parts of the body underneath the skin).
Inflammatory Bowel Disease (IBD): A general term for any disease characterised by inflammation of the bowel.
Investigational vaccine: A vaccine that has been approved by the Food and Drug Administration (FDA) for use in clinical trials on humans.
Jaundice: Yellowing of the skin and eyes. This condition is often a symptom of hepatitis infection.
Lupus: A disease characterized by inflammation of the connective tissue (which supports and connects all parts of the body). The disease begins with fever, joint pain and fatigue. Additional symptoms continue to develop over the years including nausea, fatigue, weight loss, arthritis, headaches and epilepsy. Problems with heart, lung and kidney function may also result. This condition is diagnosed most frequently in young women but also occurs in children.
Lyme disease: A bacterial disease transmitted by infected ticks with symptoms such as fatigue, chills, fever, headache, joint and muscle pain, swollen lymph nodes and a skin rash (in a circular pattern). Long-term problems include arthritis, nervous system abnormalities, irregular heart rhythm and meningitis. Lyme disease can be treated with antibiotics.
Lymphocytes: Small white blood cells that help the body defend itself against infection.
Macrophage: A large cell that helps the body defend itself against disease by surrounding and destroying foreign organisms.
Memory Cells: A group of cells that help the body defend itself against disease by remembering prior exposure to specific organisms. Memory cells are able to respond quickly when these organisms repeatedly threaten the body.
Meningitis: Inflammation of the brain and spinal cord that can result in permanent brain damage and death.
Meningoencephalitis: Inflammation of the brain and meninges (membranes) that involves the encephalon (area inside the skull) and spinal column.
Microbes: Tiny organisms that can only be seen with a microscope.
Mop-up campaigns: Door-to-door immunisation campaigns target to districts where final pockets of poliovirus transmission have been identified.
Mucosal membranes: The soft, wet tissue that lines body openings specifically the mouth, nose, rectum and vagina.
Multiple Sclerosis: Multiple sclerosis (MS) is a disease of the central nervous system characterised by the destruction of the myelin sheath surrounding neurons, resulting in the formation of "plaques."
Neuritis: Inflammation of the nerves.
Neuropathy: A general term for any dysfunction in the peripheral nervous system. Symptoms include pain, muscle weakness, numbness, loss of coordination and paralysis. This condition may result in permanent disability.
Optic neuritis: A medical condition where vision deteriorates rapidly over hours or days. One or both eyes may be affected.
Orchitis: A complication of mumps infection occurring in males (who are beyond puberty). Symptoms begin 7-10 days after onset of mumps and include inflammation of the testicles, headache, nausea, vomiting, pain and fever.
Otitis media: A viral or bacterial infection that leads to inflammation of the middle ear. This condition usually occurs along with an upper respiratory infection. Symptoms include earache, high fever, nausea, vomiting and diarrhea. In addition, hearing loss, facial paralysis and meningitis may result.
Outbreak: Sudden appearance of a disease in a specific geographic area (e.g. neighborhood or community) or population.
Pandemic: Refers to diseases that spread across wide geographic areas. A pandemic is an epidemic that occurs throughout a wide region or even throughout the world.
Papular: Marked by small red-colored elevation of the skin.
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 measles antibodies are passed to the infant prior to birth. These antibodies temporarily protect the baby for the first 4-6 months of life.
Pathogens: Organisms that cause disease in human beings.
Placebo: A substance or treatment that has no effect on human beings.
Pneumonia: Inflammation of the lungs characterized by fever, chills, muscle stiffness, chest pain, cough, shortness of breath, rapid heart rate and difficulty breathing.
Poliomyelitis: Polio is an acute infectious viral disease characterized by fever, paralysis, and atrophy of skeletal muscles.
Polysaccharide vaccines: Vaccines that are 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.
Potency: A measure of strength.
Prevalence: The number of disease cases (new and existing) within a population over a given time period.
Prodromal: An early symptom indicating the onset of an attack or a disease.
Quarantine: 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.
Recombinant: Of or resulting from new combinations of genetic material or cells; the genetic material produced when segments of DNA from different sources are joined to produce recombinant DNA.
Reye Syndrome: Encephalopathy (general brain disorder) in children following an acute illness such as influenza or chickenpox. Symptoms include vomiting, agitation and lethargy. This condition may result in coma or death.
Reservoir: An organism that harbours pathogenic organisms harmless to their host but may serve as a reservoir of infection for other individuals.
Risk: The likelihood that an individual will experience a certain event.
Salk strains: Wild poliovirus strains used in the production of IPV.
Serious adverse event (SAE): Is any untoward medical occurrence that at any dose, results in death, is life threatening, requires inpatient hospitalization, or prolongation of existing hospitalization, results in persistence or significant disability/incapacity, or is a congenital anomaly/birth defect/Medical and scientific judgement should be exercised in deciding whether expedited reporting is appropriate in other situations, such as important medical events that may not be immediately life-threatening or result in death or hospitalization but may be jeopardize the patient or may require intervention to prevent one of the other outcomes listed in the definition above. These should also usually be considered serious. (The term "life-theatning" in the definition of "serious" refers to an event, which hypothetically might have cause death if it were more severe.).
Seroconversion: Development of antibodies in the blood of an individual who previously did not have detectable antibodies.
Seroprotection: Antibody level that is sufficient to confer protection against a specific disease.
Serology: Measurement of antibodies, and other immunological properties, in the blood serum.
Serosurvey: Study measuring a population's risk of developing a particular disease.
Seizure: The sudden onset of a jerking and staring spell usually caused by fever. Also known as convulsions.
Severe Combined immune Deficiency (SCID): Included in a group of rare, life-threatening disorders caused by at least 15 different single gene defects that result in profound deficiencies in T- and B- lymphocyte function.
Side Effect: Undesirable reaction resulting from immunization.
Strain: A specific version of an organism.
Sudden Infant Death Syndrome (SIDS): The sudden and unexpected death of a healthy infant under 1 year of age. A diagnosis of SIDS is made when an autopsy cannot determine another cause of death.
Susceptible: Unprotected against disease.
Temporal association: Two or more events that occur around the same time but may be unrelated, chance occurrences.
Thimerosal: Is a mercury-containing preservative used in some vaccines and other products. There is no convincing evidence of harm caused by the low concentrations of thimerosal in vaccines, except for minor reactions like redness and swelling at the injection site.
Vaccination: Injection of a killed or weakened infectious organism in order to prevent the disease.
Vaccinia: A virus related to the smallpox and cowpox viruses, which is used in smallpox vaccine.
Vaccine effectiveness: Ability of a vaccine to reduce the incidence of disease in real-life conditions. Vaccine effectiveness is determined after use of the vaccine in national immunisation programmes.
Vaccine efficacy: Ability to reduce the incidence of disease as measured in a clinical research/trial settings.
Vesicular: Characterized by small elevations of the skin containing fluid (blisters).
Viremia: The presence of a virus in the blood.
Virulence: The relative capacity of a pathogen to overcome body defenses.
Virus: A tiny organism that multiplies within cells and causes disease such as chickenpox, measles, mumps, rubella, pertussis and hepatitis. Viruses are not affected by antibiotics, the drugs used to kill bacteria.
Waning Immunity: The loss of protective antibodies over time.
Page created on 16 March 2015
Page last reviewed on 29 March 2017
References: Centers for Disease Control and Prevention (CDC), scientific databases and journals.
Vaccines for Africa Initiative (VACFA)
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