- Acellular pertussis vaccine
A preparation of subunit proteins from pertussis bacteria, used to immunize against pertussis.
A pharmacological agent (e.g., aluminum salt, oil-in-water emulsions) that modifies the effect of other agents, such as a drug or vaccine, while having few if any direct effects when given by itself. Adjuvants are often included in vaccines to enhance the recipient's immune response to a supplied antigen, while keeping the injected foreign material to a minimum.
- ADR surveillance
A surveillance system designed to collect adverse drug reactions following administration of a drug used for prophylaxis, diagnosis, or therapy of diseases, or for the alteration of a physiological process. This type of surveillance typically relies on health professionals associating an adverse reaction in an individual as a possible consequence of the drug and reporting it to the national pharmacovigilance centre, NRA or appropriate authority.
A drug used to treat severe allergic reaction (anaphylaxis). Also a hormone produced by the adrenal gland.
- Adverse drug reaction
Adverse drug reaction (ADR)
A response to a drug that is noxious and unintended and occurs at doses normally used in man for the prophylaxis, diagnosis or therapy of disease, or for modification of physiological function.
- Adverse event
Adverse event (or adverse experience)
Any untoward medical occurrence that may appear during treatment with a pharmaceutical product but which does not necessarily have a causal relationship with the treatment.
- Adverse event following immunization
Adverse event following immunization (AEFI)
Any untoward medical occurrence which follows immunization and which does not necessarily have a causal relationship with the usage of the vaccine. The adverse event may be any unfavourable or unintended sign, abnormal laboratory finding, symptom or disease. AEFI is used in accordance with "Definition and Application of Terms for Vaccine Pharmacovilance", a report of CIOMS/WHO, working group on Vaccine Pharmacovigilance: https://cioms.ch/wp-content/uploads/2017/01/report_working_group_on_vaccine_LR.pdf.
- Adverse event of special interest
Adverse event of special interest (AESI)
A relatively new AEFI classification that started with pandemic vaccine development. AESI refers to adverse events of significant scientific, medical, and public interest among pandemic vaccines.
- AEFI surveillance
AEFI surveillance (also known as vaccine safety surveillance)
A surveillance system designed to collect adverse events temporally associated with receipt of vaccines. This type of surveillance typically relies on health professionals associating an adverse event in an individual as a possible consequence of vaccination and reporting it to the NRA or appropriate authority.
An acute, multi-system, allergic reaction (IgE mediated) to a substance, such as vaccination, drugs, and food. Symptoms of anaphylaxis may include breathing difficulties, loss of consciousness, and a drop in blood pressure. This condition can be fatal and requires immediate medical attention.
A substance that kills or inhibits the growth of bacteria. Antibiotics (in trace amounts) are used during the manufacturing phase of some vaccines to prevent bacterial contamination of the tissue culture cells.
A special protein produced by plasmocytes in response to antigens (foreign substances, e.g., bacteria or viruses). Antibodies bind with antigens on microorganisms as one of the initial steps of the body's protection against infection.
A foreign substance in the body that triggers the production of antibodies.
Chronic respiratory disease characterized by constriction of the bronchial tubes to the lungs, which causes sudden and recurring breathing problems, coughing, chest tightness and wheezing.
- Asymptomatic carriage
An infection or colonization by a pathogen that does not cause symptomatic disease.
A genetic predisposition toward the development of immediate hypersensitivity reactions against common environmental antigens (atopic allergy), most commonly manifested as allergic rhinitis but also as bronchial asthma, atopic dermatitis, or food allergy.
- Attenuated vaccine
See Live attenuated vaccine
A chronic neural development 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. At this time, the cause of autism is not known.
- Auto-disable syringes
Auto-disable (AD) syringes
AD syringes are self-locking syringes that can be used only once. AD syringes are the preferred equipment for immunizations requiring injections.
- Autoimmune disorders
A condition that occurs when the immune system mistakenly attacks and destroys healthy body tissue. There are more than 80 different types of autoimmune disorders.
- Bacillus Calmette-Guérin
See Tuberculosis vaccine.
Single-celled life-forms that can reproduce quickly on their own. Some bacteria cause disease.
- Bacterial carriage
A bacterial infection or colonization that does not cause symptomatic disease.
- Bacterial meningitis
Inflammation of the membranes that surround the brain and spinal cord; caused by a bacterial infection.
- BCG osteitis
A rare reaction from BCG vaccination, causing inflammation of the bone.
- Bell's palsy
Paralysis of one of the facial nerves (the nerves that supply muscles on the face), due to unknown cause. It is characterized by an asymmetric facial expression, due to the paralysis of one side. Several conditions can cause a facial paralysis, e.g., viral infections, brain tumor, stroke, and Lyme disease. However, if no specific cause can be identified, the condition is known as Bell's palsy.
A medical product prepared from biologic material of human, animal, or microbiologic origin (e.g., blood products, vaccines, insulin).
- Biosynthetic technology
A method for producing a chemical compound using a living organism.
- Booster injection
An additional vaccine dose needed to "boost" (increase) antibody levels after completion of the primary immunization, which may be a series of up to three doses.
- Brachial neuritis
A neuropathy that presents as a deep, steady, often severe aching pain in the shoulder and upper arm and may include muscular weakness.
Abnormally slow heartbeat.
- Brighton Collaboration
An international voluntary collaboration to facilitate the development, evaluation, and dissemination of high quality information about the safety of human vaccines. For more information, see https://brightoncollaboration.us.
Substances that minimize changes in the acidity of a solution when an acid or base is added to the solution. Buffers are used in the manufacturing process of some vaccines.
- Burden of disease
Burden of disease
The impact of a disease in a defined population, usually expressed in terms of mortality or morbidity rates, or some other measure such as years of healthy life lost or disability adjusted life years (DALYs).
- Carrier protein
A protein linked to a weak antigen to increase its immunogenicity when used as a vaccine.
- Case control study
Case control study
Study that compares a group of persons with an outcome of interest (e.g., a disease, health condition, unintended drug response) to a control group of people without it. The two groups are compared for differences in past exposures (e.g., drugs, vaccines) or other pre-existing conditions that might explain the difference in outcome.
- Causality assessment
Causality assessment (or causality association)
The systematic review of data about an AEFI case to determine the likelihood of a causal association between the event and the vaccine(s) received.
- Cell-mediated immunity
An immune response not involving antibodies, in which specific blood cells, leukocytes, and lymphocytes attack and remove antigens.
- Challenge, dechallenge and rechallenge
Challenge, dechallenge and rechallenge
A testing protocol in which a medicine or drug is administered, withdrawn, then re-administered, while being monitored for adverse effects at each stage. It is one of the standard means of assessing adverse drug reactions but is usually not possible in vaccine trials or AEFI investigations.
An acute infectious disease of the small intestine, caused by the bacterium Vibrio cholerae and characterized by profuse watery diarrhea, vomiting, muscle cramps, severe dehydration, and depletion of electrolytes.
- Chronic fatigue syndrome (CFS)
A debilitating and complex disorder characterized by profound fatigue of six months or longer duration that is not improved by bed rest and that may be worsened by physical or mental activity. Persons with CFS most often function at a substantially lower level of activity than they were capable of before the onset of illness. In addition to these key-defining characteristics, patients report various nonspecific symptoms, including weakness, muscle pain, impaired memory and/or mental concentration, insomnia, and post-exertional fatigue lasting more than 24 hours. In some cases, CFS can persist for years.
- Clinical efficacy
The ability of a medical intervention (e.g., vaccine, drug, procedure) to produce the desired clinical effect (e.g., protection, cure, symptomatic relief).
- Clinical trial
A systematic study of a medical intervention in human subjects (including patients and other volunteers) in order to discover or verify the effects of and/or identify any adverse reaction to the intervention. Clinical trials also study the absorption, distribution, metabolism, and excretion of the products with the objective of ascertaining their efficacy and safety. Clinical trials are generally classified into Phases I to IV. Phase IV trials are studies performed after the licensure and introduction of pharmaceutical products. They are carried out to expand the evidence base of the product characteristics for which the marketing authorization was granted.
Two or more instances of an event related in time, place, population subgroup, or common exposure (e.g., vaccine). AEFI clusters are usually associated with a particular provider, health facility, and/or a vial of vaccine that has been inappropriately prepared or contaminated.
- Coincidental event
An AEFI classification referring to an adverse event that occur after a vaccination has been given but are not caused by the vaccine or its administration.
- Cold chain
A system used to transport vaccines at a constant temperature involving a chain of refrigerators and portable cool boxes. Most vaccines and diluents need to be transported and stored in a cold chain between 2°C to 8°C.
- Combination or combined vaccine
Combination or combined vaccine
A vaccine that consists of two or more antigens in the same preparation (e.g., MMR, DTP).
- Confounding factor
A confounding factor is anything that is coincidentally associated with an event (for example, an AEFI), which may mislead the investigator into wrongly concluding that it is influencing the rate of an adverse vaccine reaction.
A condition that is present at birth, though not necessarily hereditary.
- Conjugated vaccine
A vaccine in which two compounds (usually a protein and polysaccharide) have been joined together to increase the vaccine's effectiveness.
- Conjugation technology
A vaccine technology in which two compounds (usually a protein and polysaccharide) are joined together to increase the vaccine's effectiveness.
A condition that makes a particular treatment or procedure, such as vaccination with a particular vaccine, inadvisable. Contraindications can be permanent, such as known allergies to a vaccine component, or temporary, such as an acute febrile illness.
- Controlled study
A study that compares a group with an exposure or outcome of interest with a group that does not have the exposure or outcome. When study subjects are randomly assigned to exposed or unexposed groups by the study researcher (e.g., are assigned to receive or not receive a vaccine or drug) and subsequent differences in outcomes measured, the study is called a randomized clinical trial. Studies in which exposure status is not controlled by researchers are called ‘observational’ and include cohort and case-control studies.
This refers to a type of economic analysis that allows comparison of different intervention options by estimating the cost per health outcome for each alternative intervention. It indicates which interventions provide the greatest impact for a given cost.
The case in which the cost of an intervention (e.g., the cost of delivering a vaccine) is less than the cost of not intervening (e.g., the cost of disease in the absence of vaccination). In this example, the intervention saves money.
- Crohn's disease
A chronic medical condition characterized by inflammation of the bowel. Symptoms include abdominal pain, diarrhea, fever, loss of appetite, and weight loss. The cause of Crohn's disease is not yet known, but genetic, dietary, and infectious factors may play a part.
- Depot effect
Some adjuvants used in injectable vaccine formulations act as a storage depot for the antigen, allowing its slow release and gradual absorption into the body; this depot effect maximizes the immune response to the vaccine.
A chronic health condition in which the body is unable to produce insulin and properly break down sugar (glucose) in the blood. Symptoms include hunger, thirst, excessive urination, dehydration, and weight loss. Treatment of diabetes requires daily insulin injections or other diabetes medication, proper nutrition, and regular exercise. Complications can include heart disease, stroke, neuropathy, poor circulation leading to loss of limb, vision problems, and death.
A fluid provided in a vial or ampoule that is mixed with lyophilized vaccine powder before the vaccine can be injected. Diluents are not interchangeable. Vaccines have different diluents; mixing and administering the wrong diluent with a vaccine has led to serious adverse events including death.
A disease caused by toxigenic strains of Corynebacterium diphtheriae. Often marked by the formation of a false membrane in the throat, diphtheria is a serious vaccine-preventable disease that can cause death in unvaccinated children.
- Diphtheria toxoid vaccine
A vaccine containing diphtheria toxoid, used to immunize against diphtheria.
- Disseminated BCG infection
Disseminated BCG infection
Tuberculosis (BCG) vaccine-induced infection that is spread over a large area of the body, a tissue, or an organ. This can result in death (referred to as Fatal disseminated BCG infection).
The relationship between the dose of an active substance (e.g. a vaccine or drug) or radiation exposure, and the response in the body of exposed individuals.
Drug (or medicine)
Any substance in a pharmaceutical product that is used to modify or exploit physiological systems or pathological states for the benefit of the recipient. The term drug/medicinal product is used in a wider sense to include the whole formulated and registered product, including the presentation and packaging, and the accompanying information. Vaccines are drugs/medicines.
- DT vaccine
A preparation of diphtheria and tetanus toxoids together in one vaccine, used to immunize children and adolescents against diphtheria and tetanus. The DT vaccine given to adults contains a reduced amount of diphtheria toxoid.
- DTaP vaccine
A combination of diphtheria and tetanus toxoids with acellular pertussis vaccine together in one vaccine, used to immunize against diphtheria, tetanus, and pertussis.
- DTP vaccine
A combined preparation of diphtheria and tetanus toxoids with pertussis vaccine together in one vaccine, used to immunize against diphtheria, tetanus, and pertussis (also sometimes referred to as DPT vaccine). When an acellular pertussis vaccine is used, the combination is usually abbreviated DTaP. When the whole cell pertussis vaccine is used, the combination is usually abbreviated DTwP.
- DTwP vaccine
A combination of diphtheria and tetanus toxoids with whole cell pertussis vaccine together in one vaccine, used to immunize against diphtheria, tetanus, and pertussis.
See Vaccine effectiveness.
See Vaccine efficacy.
Reduction to zero (or a very low defined target rate) of new cases of an infectious disease in a defined geographical area as a result of deliberate efforts; continued measures to prevent re-establishment of transmission are required.
A mixture of two liquids that do not mix resulting in one of the liquids dispersed throughout the other in small droplets.
Refers to an encephalopathy caused by an inflammatory response in the brain. This is usually manifested with systemic constitutional symptoms, particularly fever and pleocytosis of the cerebrospinal fluid. However, the terms encephalopathy and encephalitis have been used imprecisely and even interchangeably in the literature.
Refers to a variety of conditions affecting the brain resulting in alterations in the level of consciousness, ranging from stupor to coma. At times, febrile seizures, afebrile seizures, and epilepsy have been considered components of encephalopathy. However, the terms encephalopathy and encephalitis have been used imprecisely and even interchangeably in the literature.
A toxin contained in the cell walls of some microorganisms, especially gram-negative bacteria, that is released when the bacterium dies and is broken down in the body. Fever, chills, shock, and a variety of other symptoms may result, depending on the particular organism and the condition of the infected person.
The occurrence of disease within a geographical area and/or population that is in excess of what is normally expected for a given period of time.
The study of the distribution and determinants of health and disease in human populations.
A substance extracted from horses, e.g. some antibodies used in passive immunization are extracted from the serum of horses exposed to the target antigen.
The complete and permanent worldwide reduction to zero new cases of an infectious disease through deliberate efforts; no further control measures are required.
Research based on systematic investigation of the outcomes of controlled interventions; the results have been verified by other researchers using the same methods.
- Expanded Programme on Immunization
Expanded Programme on Immunization (EPI)
An international programme launched by WHO in 1974 to increase immunization of the world's children. EPI originally targeted vaccines for six diseases: measles, diphtheria, pertussis, tetanus, tuberculosis and poliomyelitis. EPI and national immunization programme (NIP) are used interchangeably.
- Fatal dissemination of BCG infection
Fatal dissemination of BCG infection
Tuberculosis (BCG) vaccine-induced infection that is spread over a large area of the body, a tissue, or an organ, and results in death.
Relating to fever; feverish. A febrile seizure is a seizure or convulsion that occurs during a high fever. Common in children under five years of age, rarely resulting in long term injury.
- Freund's adjuvant
A water-in-oil emulsion added to some vaccines to increase the immune response to the vaccine antigen.
- Global Advisory Committee on Vaccine Safety
Global Advisory Committee on Vaccine Safety (GACVS)
Established in 1999, the GACVS advises the WHO on vaccine-related safety issues and enables WHO to respond promptly, efficiently, and with scientific rigor to issues of vaccine safety with potential global importance. The committee also assesses the implications of vaccine safety for practice worldwide and for WHO policies. For more information, see http://www.who.int/vaccine_safety/en/.
- Good manufacturing practice
Good manufacturing practice (GMP)
Guidelines that outline the aspects of production that would affect the quality of a product. Many countries have legislated that pharmaceuticals, biologicals, and medical device companies must follow GMP procedures, and have created their own GMP guidelines that correspond with their legislation to assure the quality of those products. WHO also proposes GMP guidelines that are used by many countries.
- Guillain-Barré Syndrome
A rare neurological disease characterized by loss of reflexes and temporary paralysis. Symptoms include weakness, numbness, tingling, and sensitive disorders that spreads over the body. Muscle paralysis starts in the feet and legs and moves upwards to the arms and hands. Sometimes paralysis can result in the respiratory muscles causing breathing difficulties. Symptoms usually appear over the course of one day and may continue to progress for three or four days up to three or four weeks. Recovery begins within two to four weeks after the progression stops. While most patients recover, approximately 15 to 20% experience persistent symptoms. GBS is fatal in 5% of cases.
- Haemophilus influenzae type b
Bacteria that can cause serious invasive illnesses, such as pneumonia and meningitis; most common in children and persons who are immune compromised (less able to fight off infections). Hib is one of six types of bacteria that are major causes of bacterial meningitis in unimmunized infants.
- Haemophilus influenzae type b vaccine
A subunit polysaccaride-conjugate vaccine used to immunize against invasive Hib disease.
- Hepatitis B
A viral infection of the liver that is transmitted through contact with blood or other body fluids that are infected with the hepatitis B virus. Some infections, especially those acquired in infancy, can become chronic and result in cirrhosis and primary liver cancer in adulthood.
- Hepatitis B vaccine
Hepatitis B vaccine (HepB)
A subunit protein-based recombinant vaccine used against hepatitis B infection.
- Herd effect
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 results from a small proportion of susceptible individuals in a population making it difficult for the infectious agent to sustain circulation.
- Herd immunity
A population with a high proportion of individuals with immunity to a particular pathogen, as a consequence of immunization or infection and recovery, may confer protection from infection on the small proportion of its non-immune members because there are too few susceptible people in the 'herd' for the infection to circulate.
- Herpes zoster
An inflammatory disease, also known as the shingles, caused by the same virus that causes chicken pox. Some people exposed to this virus during childhood develop partial immunity. After the primary infection as chicken pox the virus becomes dormant, reactivating years or decades later as herpes zoster. It is characterized by painful skin lesions that occur mainly on the trunk (back and stomach) of the body but which can also develop on the face and in the mouth.
Acquired immune deficiency syndrome (AIDS) is a collection of symptoms and infections resulting from the specific damage to the immune system caused by the human immunodeficiency virus (HIV).
All embracing, taking into account all aspects of a situation; in healthcare, holistic usually refers to a commitment to consider all aspects of the patient's situation, including social and psychological states as well as medical conditions.
An excessive or abnormal sensitivity in a body tissue to an antigen or foreign substance.
High blood pressure.
Low blood pressure.
- Hypotonic hyporesponsive episode
A recognized serious reaction to immunization, especially pertussis-containing vaccine. It is defined as an acute loss in sensory awareness or loss of consciousness accompanied by pallor and muscle hypotonicity. No long-term sequelae have been identified in the small number of children who have had long term follow-up. HHE is not a contraindication for further doses of pertussis vaccine.
- Immune response
The body's defense against foreign objects or organisms, such as bacteria, viruses or transplanted organs or tissue.
- Immune system
A complex system of organs and processes in the body responsible for fighting disease. Its primary function is to identify foreign substances in the body (including bacteria, viruses, fungi, parasites or transplanted organs and tissues) and develop a defense against them. This defense is known as the immune response.
The body's response mechanism for fighting against bacteria, viruses and other foreign substances. If a cell or tissue (such as bacteria or a transplanted organ) is recognized as not belonging to the body, the immune system will act against the "invader." The immune system is the body's way to fight external invasions.
The process by which a person or animal becomes protected against a disease through an enhancement of their immune response. This term is different from vaccination which is a form of immunization where the body learns to recognize a particular foreign object (active immunization). Passive immunization can be provided by administering external antibodies that will temporarily help strengthen the body's response without inducing memory against a specific foreign object.
Immunization anxiety-related reaction
An AEFI arising from anxiety about the immunization.
- Immunization error
An AEFI classification that refers to events caused by errors in vaccine preparation, handling, or administration.
- Immunization safety
The process of ensuring and monitoring the safety of all aspects of immunization, including vaccine quality, vaccine storage and handling, vaccine administration, disposal of sharps, and management of waste.
Unable to mount a normal immune response. This condition can be genetic, or caused by disease (like HIV infection or cancer) by certain drugs (such as those used in chemotherapy and organ transplantation). Individuals whose immune systems are severely compromised should not receive LAV vaccines.
The power of an antigen to induce an immune response.
- Inactivated polio vaccine
Inactivated polio vaccine (IPV)
An inactivated (killed) polio vaccine, developed in 1955 by Dr. Jonas Salk. Unlike oral polio vaccine (OPV), a LAV vaccine, IPV must be injected to produce the desired immune response.
- Inactivated vaccine
Inactivated vaccine (also known as killed vaccine)
A vaccine made from microorganisms (viruses, bacteria, other) that have been killed through physical or chemical processes. These killed organisms cannot cause disease.
The number of new cases (e.g., of a disease, adverse event) occurring in a defined population during a given time interval, often one year.
- Individual case safety report
Individual case safety report (ICSR)
A report received by a company or agency that describes an adverse event.
- Infammatory bowel disease
Infammatory bowel disease
A general term for any disease characterized by inflammation of the bowel; examples include colitis and Crohn's disease. Symptoms include abdominal pain, diarrhea, fever, loss of appetite, and weight loss.
A highly contagious viral infection characterized by sudden onset of fever, aches and pains, and inflammation of mucous membranes.
- Informed consent
An ethical requirement that an idividual who gives consent for an invasive medical procedure (e.g. a vaccination) is fully informed of all relevant risks and benefits of the procedure before making the decision to consent.
The practice of intentionally exposing someone to matter from smallpox pustules in order to initiate a mild, protective response to the disease.
A hormone secreted by the islets of Langerhans and functioning in the regulation of the metabolism of carbohydrates and fats, especially the conversion of glucose to glycogen, which lowers the blood glucose level. It is also available as a pharmaceutical for the treatment of diabetes.
- Intramuscular injection
Intramuscular (IM) injection
Administration of vaccine into the muscle mass. Vaccines containing adjuvants should be injected IM to reduce the depot effect and formation of granulomas.
- Intranasal influenza
A live attenuated influenza vaccine, administered through the nose. Advantages of this vaccine include easier and more acceptable administration than injection and possibly the stimulation of a broader immune response in some age groups.
A potentially life threatening obstruction of the bowel. When the first rotavirus vaccine was licensed in 1999, it was withdrawn from the market following evidence linking it to a small increase in the risk of intussusception.
- Japanese encephalitis
A mosquito-borne viral infection, the leading cause of viral encephalitis in Asia.
- Japanese encephalitis vaccine
Two vaccines against JE are currently available internationally: the inactivated, mouse-brain derived JE vaccine and the live attenuated SA-14-14-2 JE vaccine.
- Key message
A key message gives the most important information that you want the public to know, for example in relation to a health education campaign on the benefits of vaccination.
- Killed vaccine
See Inactivated vaccines.
Large linked databases (LLDBs)
Administrative databases of relatively large size that were created separately from each other and linked to enable the sharing of data across platforms. Such linked databases have become popular in vaccine safety surveillance where specific disease's occurrence can be linked to a person's vaccination history.
Any of a group of neoplastic diseases of the blood-forming organs, resulting in an abnormal increase in the production of leukocytes, often accompanied by anemia and enlargement of the lymph nodes, spleen, and liver.
The granting of a license to conduct a regulated procedure, for example, to conduct a trial of a new vaccine or to approve a vaccine for routine delivery to the public in a vaccination programme.
- Live attenuated vaccine
Live attenuated vaccine (LAV)
A vaccine prepared from living micro-organisms (viruses, bacteria currently available) that have been weakened under laboratory conditions. LAV vaccines will replicate in a vaccinated individual and produce an immune response but usually cause mild or no disease.
Local (or localized)
Restricted or limited to a specific body part or region.
Lot (or lot-release)
Vaccines are produced in "lots" or batches. Prior to releasing a "lot" of vaccine for public use, the NRA provides a vital check on the manufacturer’s performance. As a minimum, lot release should be based on review of the summary lot protocols, which contain details of that particular lot. In addition, selected laboratory testing can be carried out. Lot release should be included in the regulations that cover biological products.
Lymphadenitis is the inflammation and/or enlargement of one or more lymph nodes. Most cases indicate an immune response in the node to local infection or antigen stimulation, for example in a vaccine. Generalised lymphadenitis is a widespread inflammation of the lymph nodes due to systemic (circulating) infection.
Freeze-dried; e.g. measles and BCG vaccines are transported as lyophilized powders which must be reconstituted with specific liquid diluents before use as injectable vaccines. Lyophilised vaccines must be discarded within 6 hours of reconstitution, or at the end of a vaccination session, whichever comes first.
- Macrophagic myofasciitis
A disease causing muscle pain, joint pain, muscle weakness, fatigue, fever, and muscle tenderness. It is characterized by microscopic muscular infiltration with macrophages. Specific causes are unknown, but the disease has been associated with the persistence of aluminum hydroxide used in some vaccines. The diagnosis can only be confirmed through a muscle biopsy.
An infectious disease caused by a parasite (plasmodium) that is transmitted from human to human by the bite of infected female Anopheles mosquitoes. Malaria is a leading cause of morbidity and mortality in sub-Saharan Africa.
A contagious viral disease marked by fever, the eruption of red circular spots on the skin that can be deadly to young and weakened individuals.
- Measles vaccine
A preparation of live attenuated measles virus used to immunize against measles.
- Meningococcal disease
Bacterial diseases caused by the meningococcus (Neisseria meningitidis). Meningococcal diseases include clinical forms of the disease, in particular meningitis, sepsis and pneumonia.
Tiny organisms (including bacteria and viruses) that can only be seen with a microscope.
- Minor vaccine reaction
Minor (or mild) vaccine reaction
Vaccine reactions that usually occur within a few hours of injection, resolve after a short period of time, and pose little danger.
- MMR vaccine
A preparation of live attenuated measles, mumps, and rubella viruses together in one vaccine, used to immunize against measles, mumps, and rubella.
- Monovalent vaccine
A monovalent vaccine is designed to immunize against a single antigen or single microorganism whereas polyvalent vaccines aim to immunize against several strains of the same microorganism, or against several microorganisms.
- MR vaccine
A preparation of live attenuated measles and rubella viruses together in one vaccine, used to immunize against measles and rubella.
- Multiple Sclerosis
A disease of the central nervous system characterized by the destruction of the myelin sheath surrounding neurons, resulting in the formation of "plaques." The cause of MS is unknown, although it appears to require a genetic susceptibility combined with an environmental ‘trigger’, possibly a viral infection. While extensively investigated, there is no epidemiologic evidence to support a link between vaccination and onset or recurrence of MS.
An acute contagious viral illness marked by swelling, especially of the parotid glands.
- National immunization programme
National immunization programme (NIP)
The organizational component of government Ministries of Health charged with preventing disease, disability, and death from vaccine-preventable diseases in children and adults. NIP is used interchangeably with the Expanded Programme on Immunization (EPI) that originally focused on preventing vaccine-preventable diseases in children.
- National immunization technical advisory groups
National immunization technical advisory groups (NITAGs)
Advisory groups whose general objective is to guide national governments and policy-makers to develop and implement evidence-based, locally relevant immunization policies and strategies that reflect national priorities.
- National pharmacovigilance centre
National pharmacovigilance centre
A governmentally recognized centre (or integrated system) within a country with the clinical and scientific expertise to collect, collate, analyze, and give advice on all information related to drug safety.
National regulatory authority (NRA)
The regulatory body that approves procedures to ensure that medicines, including vaccines, are of adequate safety and potency. The vaccine manufacturer is responsible for demonstrating that the vaccine batch produced meets the requirements, based on the test specifications given by the NRA. The NRA is also responsible both for the official vaccine lot release process, based on the data and information provided by the manufacturer and, eventually, for confirmatory testing.
The death of living cells or tissues.
- Neisseria meningitidis
A bacterium that causes meningitis, as well as infections elsewhere in the body.
A broad-spectrum antibiotic that is used in the manufacture of some vaccines.
- Neonatal tetanus
Tetanus that occurs in a newborn infant.
Inflammation of the nerves.
- Neurodevelopmental disorders
A disorder of neural development, an impairment of the growth and development of the brain or central nervous system.
A general term for any dysfunction in the nervous system. Symptoms include pain, muscle weakness, numbness, loss of coordination, and paralysis. This condition may result in permanent disability.
The presence of an excessive amount of fluid in or around cells, tissues, or serous cavities of the body.
- Options analysis
A system for ranking multiple options in order to decide the best course of action in the prevailing circumstances.
- Oral polio vaccine
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).
- Otitis media
An inflammation of the middle ear usually caused by a virus or a bacteria. This condition usually occurs in conjunction with an upper respiratory infection. Symptoms include earache, high fever, nausea, vomiting, and diarrhea. In addition, hearing loss, facial paralysis, and meningitis may result.
A hormone secreted by the posterior pituitary gland that stimulates contractions of the uterus and ejection of milk. As a pharmaceutical it is used in childbirth and lactation to cause muscles to contract in the uterus (womb) and mammary glands in the breast.
- Pan-American Health Organization
Pan-American Health Organization (PAHO) Revolving Fund for Vaccine Procurement
A mechanism developed by PAHO in 1979 for the purchase of vaccines, syringes/needles, and cold chain equipment for countries in Latin America and the Caribbean. Through a system of bulk purchasing, the Fund has secured for the past 30 years a supply of high quality vaccines for national immunization programs at affordable prices, and it has also allowed for the orderly planning of immunization activities.
An epidemic occurring over a very large area and affecting a large number of people.
A widely used over-the-counter analgesic (pain reliever) and antipyretic (fever reducer).
- Passive reporting
See Passive surveillance.
- Passive surveillance
Passive surveillance (also known as spontaneous reporting)
A surveillance system designed to collect adverse events that follow vaccination. This type of surveillance typically relies on health professionals noticing and reporting adverse events in individuals after vaccination to the NRA or appropriate authority.
Any disease-causing substance. Most commonly used for organisms (e.g., bacteria, viruses) and their biological products (e.g. toxins).
An infectious bacterial disease caused by Bordetella pertussis that produces violent, spasmodic coughing; also called whooping cough.
- Pertussis vaccine
Two types of pertussis vaccines are currently available: the inactivated whole-cell vaccine (wP) and subunit protein-based vaccine (aP).
The science and activities relating to the detection, assessment, understanding, and prevention of adverse effects or any other drug-related problem.
- Placebo controlled
A randomized clinical trial may include controls in which some of the subjects receive a product which has no active ingredients, referred to as a placebo, e.g. a sugar pill or an injection of normal saline. None of the people in the clinical trial nor the clinical team administering the intervention know who was given the placebo, or the test product, or the best performing existing product. A placebo controlled trial enables researchers to evaluate whether the simple act of being given a pill or an injection has a beneficial effect.
A serious, potentially life-threatening infectious disease that is usually transmitted to humans by the bites of rodent fleas. It was one of the scourges of early human history.
- Pneumococcal conjugate vaccine
Three subunit polysaccarhide-conjugate vaccines exist against pneumococcus. PCV-7 vaccine protects against seven serotypes and PCV-10 protects against ten serotypes of Streptococcus pneumoniae, and PCV-13 protects agains 13 serotypes serotypes of Streptococcus pneumoniae most commonly isolated from young children.
- Pneumococcal disease
Bacterial diseases caused by Streptococcus pneumoniae. Pneumococcal diseases include meningitis, sepsis, and pneumonia, all of which cause significant illness and death.
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.
- Post-licensure surveillance
Post-licensure surveillance (also known as post-marketing surveillance)
Pharmacovigilance conducted after a product has been licensed and introduced for use in a population.
A measure of strength or immunogenicity in vaccines.
- Prequalified vaccine
A vaccine that has been approved as acceptable, in principle, for purchase by United Nations agencies, such as WHO, after full assessment of all procedures involved in its production. The purpose of the assessment is to verify that prequalified vaccines: (a) meet the specifications of the relevant UN agency; and (b) are produced and overseen in accordance with the principles and specifications recommended by WHO, for good manufacturing practice (GMP), and for good clinical practice (GCP). This is to ensure that vaccines used in national immunization services in different countries are safe and effective for the target population at the recommended schedules and that they meet particular operational specifications for packaging and presentation.
Compounds that are added to multi-dose vaccine vials to prevent bacterial and fungal growth. The most commonly used product is called thiomersal, a mercury-containing compound.
The process of artificial induction of immunity, in order to protect against infectious disease. Priming the immune system involves sensitizing or stimulating an immune response with an antigen that can produce immunity to a disease-causing organism or toxin (poison). Vaccinations involve the administration of one or more of these antigens, which can be administered in several forms.
- Programme for International Drug Monitoring
Programme for International Drug Monitoring (PIDM)
This programme, established in 1968, consists of a network of national pharmacovigilance centres, WHO Headquarters in Geneva, and the WHO Collaborating Centre for International Drug Monitoring, the Uppsala Monitoring Centre, in Uppsala, Sweden. For more information, see https://www.who-umc.org/global-pharmacovigilance/who-programme-for-international-drug-monitoring/.
A potentially fatal viral infection spread through the bite of certain warm-blooded animals. It attacks the central nervous system and, if left untreated, is highly fatal in animals.
- Randomized clinical trials
Randomized clinical trials
A systematic study of medical interventions in human subjects (including patients and other volunteers) in which study subjects are randomly assigned to treatment and control groups. Used to discover or verify the effects of and/or identify any adverse reactions to investigational products, and/or to study the absorption, distribution, metabolism and excretion of the products with the objective of ascertaining their efficacy and safety. Studies in which neither the investigator nor the study subjects know to which group, treatment or control, they have been assigned until the conclusion of the study are referred to as ‘double-blind randomized clinical trials’ and are considered the gold standard for drug and vaccine efficacy research.
Being able to produce adverse reactions.
- Reassortant vaccine
A live attenuated vaccine in which attenuation is achieved by using virus strains in which some gene sequences have been rearranged (reassorted); for example, RotaTeq vaccine contains five reassortant rotavirus strains.
- Recombinant DNA
A vaccine technology that uses genetic material from a disease-causing organism into a live vector, often a yeast cell, in order to replicate a protein antigens of the disease-causing organism. The proteins are then purified and used as vaccine.
- Reconstituted vaccine
The mixing of a powdered (usually lyophilized) form of a vaccine with a fluid called a diluent prior to injection.
An RNA virus (a virus composed not of DNA but of RNA). Retroviruses have an enzyme called reverse transcriptase that gives them the unique property of transcribing RNA (their RNA) into DNA. The retroviral DNA can then integrate into the chromosomal DNA of the host cell to be expressed there. HIV is a retrovirus.
The probability that an individual will experience a certain event during a defined period of time.
- Risk-benefit analysis
Evaluation and assessment of the relative risks and benefits of an intervention, e.g. the potential benefit of protection from measles and its complications due to vaccination, relative to the potential risk of adverse reactions to the vaccine.
A group of viruses that cause diarrhea (rotaviral gastroenteritis) in children.
- Rotavirus vaccine
A preparation of live attenuated rotavirus used to immunize against infant rotaviral gastroenteritis.
Rubella (German measles)
A viral infection that is usually milder than measles but can cause serious damage or death to a fetus when a pregnant woman is infected.
- Rubella vaccine
A preparation of live attenuated rubella virus used to immunize against rubella.
- Safety profile
A summary of the evidence on the safety of a medical product, such as a vaccine or drug, under ideal conditions of use, including the incidence of any adverse reactions relative to the number of doses given.
- Sciatic nerve
The largest nerve in the human body providing both motor and sensory control for much of the lower limbs. Vaccination of infants and children in the buttock is not recommended because of concern about potential injury to the sciatic nerve, which is well documented after injection into the buttock.
- Second opportunity
WHO recommends that all children receive two doses of measles vaccine, either through routine services or mass vaccination campaigns. Often when the second dose is delivered through campaigns, it is considered the second opportunity for measles vaccination.
Uncontrolled electrical activity in the brain, resulting in convulsion, physical signs, thought disturbances, or a combination of symptoms.
In the context of public health surveillance, the proportion of all incident cases of a health condition detected by a surveillance system.
Sepsis (also known as "blood stream infection")
The presence of bacteria (bacteremia) or other infectious organisms or their toxins in the blood (septicemia) or in other tissue of the body.
- Serious adverse event
Serious adverse event
A regulatory term defined as any untoward medical occurrence that at any dose: results in death; requires inpatient hospitalisation or prolongation of existing hospitalization; results in persistent or significant disability/incapacity; or, is life-threatening. For more information, see here.
- Severe vaccine reaction
Severe vaccine reaction
This is not a regulatory term. It refers to vaccine reactions that usually do not result in long-term problems, but can be disabling and, rarely, life threatening. Severe reactions include serious reactions but also include other severe reactions.
- Side effect
Any unintended effect of a pharmaceutical product (including vaccines) occurring at a dose normally used in man.
Reported information on a possible causal relationship between an adverse event and a drug, the relationship being previously unknown or incompletely documented. Usually more than a single report is required to generate a signal, depending upon the seriousness of the event and the quality of the information.
- Simple message
A simple message is ‘jargon free’ and easy for the general public to understand – it ‘translates’ complex concepts and information into readily accessible ideas and examples.
An acute, highly infectious, often fatal disease caused by a variola virus and characterized by high fever and aches with subsequent widespread eruption of pimples that blister, produce pus, and form pockmarks. Declared eradicated by the World Health Assembly in 1980.
An alcohol used in the manufacture of some vaccines.
In the context of surveillance, the measure of the degree to which cases detected through a surveillance system actually have the disease.
- Spontaneous reporting
See Passive surveillance.
Compounds that are used to help vaccine maintain its effectiveness during storage. Vaccine stability is essential, particularly where the cold chain is unreliable. Factors affecting stability are temperature and pH.
- Standard case definition
Standard case definition
A common, formal definition for the health-related event under surveillance. The case definition of a health-related event can include clinical manifestations (i.e., symptoms), laboratory results, epidemiologic information (e.g., person, place, and time), and/or specified behaviors, as well as levels of certainty (e.g., confirmed/definite, probable/presumptive, or possible/suspected). The use of a standard case definition increases the specificity of reporting and improves the comparability of the health-related event reported from different sources of data, including geographic areas.
A specific genetic grouping of an organism. Many organisms, such as viral influenza, pneumococcus and meningococcus, have multiple strains that cause disease.
A whistling sound generated when breathing (usually heard on inspiration) that indicates obstruction of the trachea or larynx.
- Subcutaneous injection
Administration of vaccine into the subcutaneous layer above the muscle and below the skin.
- Subunit conjugate vaccine
A vaccine in which two compounds (usually a protein and polysaccharide) are joined together to increase the vaccine's effectiveness.
- Subunit polysaccharide vaccine
A vaccine that uses portions of bacteria that are composed of long chains of sugar. Polysaccharide vaccines are available for pneumococcal disease, meningococcal disease and Hib.
- Subunit protein-based vaccine
A vaccine made from fragments of viruses or bacteria that involve a protein to increase the vaccine’s effectiveness.
- Subunit vaccine
A vaccine made from components of viruses or bacteria instead of the whole organism.
- Sudden Infant Death Syndrome
Sudden Infant Death Syndrome (SIDS) (also known as "crib" or "cot" death)
The sudden and unexpected death of a healthy infant under one year of age. A diagnosis of SIDS is made when an autopsy cannot determine another cause of death. The cause of SIDS is unknown.
- Suppurative lymphadenitis
This is a common adverse reaction to tuberculosis (BCG) vaccine and involves the inflammation of the lymph nodes associated with skin ulceration.
A chemical agent capable of reducing the surface tension of a liquid in which it is dissolved.
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.
- Surveillance system
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.
- Synthetic vaccine
A vaccine consisting mainly of synthetic peptides or carbohydrates as antigens. They are often considered to be safer than vaccines from bacterial cultures.
Relating to a system, or affecting the entire body or an entire organism (e.g., fever).
A heart rate that exceeds the normal range for a resting heart.
- Td vaccine
A preparation of tetanus and diptheria toxoids together in one vaccine used to immunize adults against diphtheria and tetanus. This vaccine contains a reduced amount of diphtheria toxoid used in the DT preparation for children. When given to women of childbearing age, vaccines that contain tetanus toxoid (TT or Td) not only protect women against tetanus, but also prevent neonatal tetanus in their newborn infants.
- Temporal association
Two or more events that occur around the same time. The preceding event may or may not be causally related to the later one.
A disease caused primarily by toxigenic C. tetani. The rare but often fatal disease affects the central nervous system by causing painful muscular contractions.
- Tetanus toxoid vaccine
Tetanus toxoid (TT) vaccine
A preparation of tetanus toxoid used to immunize against tetanus. When given to women of childbearing age, vaccines that contain tetanus toxoid (TT or Td) not only protect women against tetanus, but also prevent neonatal tetanus in their newborn infants.
Thiomersal is a mercury-containing preservative that has been used in some vaccines and other products since the 1930's. While there is no evidence that the low concentrations of thiomersal in vaccines have caused any harm other than minor reactions like redness or swelling at the injection site, in July 1999 the US Public Health Service, the American Academy of Pediatrics, and vaccine manufacturers agreed that thiomersal should be reduced or eliminated from vaccines as a precautionary measure. Today, all routinely recommended childhood vaccines manufactured for the US market contain either no thiomersal or only trace amounts.
A severe decrease in the number of blood platelets, the cells involved in clotting. Thrombocytopenia may stem from failure of platelet production, splenic sequestration of platelets, increased platelet destruction, increased platelet utilization, or dilution of platelets.
- Thrombocytopenic purpura
Severe thrombocytopenia characterized by mucosal bleeding and bleeding into the skin in the form of multiple petechiae (small purlish spot), most often evident on the lower legs, and scattered small bruises at sites of minor trauma. In children, idiopathic thrombocytopenic purpura is usually self-limited and follows a viral infection.
- Time to onset
Time to onset
The period of time between an intervention (in this case, a vaccination) and the onset of an adverse reaction to the vaccine.
- Toxic shock syndrome
Toxic shock syndrome
A rare serious adverse event resulting from improper vaccine preparation and injection practices. It is a life-threatening illness that is caused by toxins (poisons) that circulate in the bloodstream. Bacteria that have infected some part of the body release these toxins. People with toxic shock syndrome develop high fever, rash, low blood pressure, and failure of multiple organ systems in the body.
Inactivated or killed toxin (poison) used in vaccine production.
- Toxoid vaccine
A vaccine made from a toxin (poison) that has been made harmless but that elicits an immune response against the toxin.
A disease caused by the bacterium Mycobacterium tuberculosis. The bacteria usually attack the lungs. But, 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
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.
Typhoid (typhoid fever)
A serious disease caused by a bacteria called Salmonella Typhi. Typhoid causes a high fever, weakness, stomach pains, headache, loss of appetite, and sometimes a rash. If it is not treated, it can kill up to 30% of people who get it. There are different vaccines to prevent typhoid: inactivated vaccines that require injection, and live attenuated vaccines that are taken orally (by mouth).
- Uppsala Monitoring Centre
Uppsala Monitoring Centre (UMC)
An independent centre which receives adverse drug reactions from national pharmacovigilance centres in WHO member countries and generates signals of possible side-effects. For more information, see http://www.who-umc.org.
The eruption of red marks on the skin that are usually accompanied by itching. This condition can be caused by an allergy (e.g., food, vaccine, drugs), stress, infection, or physical agents (e.g., heat, cold).
Inoculation with a vaccine for the purpose of inducing immunity.
A material containing live attenuated or inactivated (killed) microorganisms, or constituents of microorganisms, capable of eliciting protection against infection.
- Vaccine Adverse Event Reporting System
Vaccine Adverse Event Reporting System (VAERS)
A passive surveillance system in the US intended to collect reports of reactions to vaccines. Under the aegis of the US Centers for Disease Control and Prevention and the US Food and Drug Administration.
- Vaccine effectiveness
The probability that a vaccine, when used in the field under routine vaccination circumstances, confers immunity in a population. Expressed as a percent.
- Vaccine efficacy
The potential of a vaccine to protect from a disease in controlled clinical trials. Expressed as a percent.
- Vaccine pharmacovigilance
The science and activities relating to the detection, assessment, understanding and communication of adverse events following immunization and other vaccine- or immunization-related issues, and to the prevention of untoward effects of the vaccine or immunization
- Vaccine reaction
Vaccine reaction (also referred to as adverse vaccine reaction or adverse reaction)
A classification of AEFI referring to events caused or precipitated by the vaccine when given correctly, caused by the inherent properties of the vaccine.
- Vaccine safety
The process of ensuring and monitoring the safety of vaccines through their life cycle.
- Vaccine safety surveillance
Vaccine safety surveillance
See AEFI surveillance.
- Vaccine-associated neurotropic disease
A very rare disease of the nervous system that follows vaccination against yellow fever.
- Vaccine-associated paralytic poliomyelitis
A very rare risk of paralytic polio resulting from oral poliomyelitis vaccine (OPV). Associated with approximately one in every 2.5 million doses of OPV. VAPP is not a risk with IPV.
- Vaccine-associated risk
The probability of an adverse or unwanted outcome occurring, and the severity of the resultant harm to the health of vaccinated individuals in a defined population, following immunization with a vaccine under ideal conditions of use.
- Vaccine-associated viscerotropic disease
A disease that presents with fever, liver damage and blood disorders that very rarely results from vaccination against yellow fever.
- Vaccine-derived poliovirus
Vaccine-derived poliovirus (VDPV)
Where polio vaccine coverage rates decline but OPV use continues, person-to-person spread of vaccine polioviruses can lead to increased virulence that resemble the wild virus.
- Vaccine-preventable diseases
Diseases for which vaccines exist that can confer partial or complete protection.
The individual receiving a vaccine.
The number of types of a microorganism that are covered in a vaccine product (e.g. seasonal influenza vaccines that typically cover three virus types are called tri-valent).
The degree to which an estimate reflects the true value of what it purports to measure.
An acute contagious disease characterized by papular and vesicular lesions.
Refers to a heterogeneous group of disorders that are characterized by inflammatory destruction of blood vessels that cause a visible rash.
- Vasovagal syncope
A neurovascular reaction that leads to fainting.
An ultramicroscopic infectious agent that consists of genetic material surrounded by a protein coat. A virus can replicate themselves only within cells of living hosts.
- Whole cell pertussis vaccine
Whole cell pertussis (wP) vaccine
A preparation of inactivated whole cell pertussis bacterium, used to immunize against pertussis.
- Wild poliovirus
A strain of poliovirus that occurs naturally, as opposed to vaccine-related strains.
- World Health Organization
World Health Organization (WHO)
A United Nations specialized agency established to coordinate international health activities and to help governments improve health services.
- Yellow fever
An infectious viral tropical disease transmitted by mosquitoes and characterized by high fever, jaundice, and gastrointestinal bleeding.
- Yellow fever vaccine
Yellow fever vaccine
A preparation of live attenuated yellow fever virus, used to immunize against yellow fever. A single dose provides protection against the disease for at least ten years and often for 30 years or more.