A running glossary of important terms to boost public health and science literacy (with links to the CDC’s glossary)


  • Active immunity: When the body’s immune system produces antibodies against a specific disease. Active immunity can be acquired by contracting the disease or through vaccination.
  • Adjuvant: A substance that is added during vaccine production to increase the body’s immune response to a given vaccine.
  • Antibody: A protein found in the blood that is produced in response to foreign substances (e.g. bacteria or viruses, see Antigen) invading the body. Antibodies protect the body from disease by specifically binding to these Antigens and destroying them.
  • Antigen: Foreign substances 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, which can sometimes fend off the disease.
  • Attenuated Vaccine: Attenuated vaccines, or live vaccines, are created when  live virus is weakened through chemical or physical processes to produce an immune response without causing the severe effects of the disease. Examples include measles, mumps, rubella (MMR), yellow fever and varicella (Chicken Pox).


  • Breakthrough infection: Breakthrough infections occur when an individual develops a disease despite a having responded to / received a vaccine.


  • Centers for Disease Control (CDC):  The CDC is the leading national public health institute within the US. It is a US federal agency under the Department of Health and Human Services and is headquartered in Atlanta, Georgia.
  • Combination vaccine: Two or more vaccines administered in a single dose in order to reduce the number of shots given, i.e. MMR (measles, mumps, rubella).
  • Communicable: Something which can be transmitted from one person or animal to another, i.e. infectious.
  • Community immunity (herd immunity): A situation in which enough of the population is immune to an infectious disease (through vaccination and/or primary infection) to make its spread from person to person unlikely and thus protect the community. Even individuals not vaccinated (such as newborns and those with chronic illnesses) are offered some protection because the potential for transmission changes through susceptible individuals is greatly reduced.
  • Conjugate vaccine: The joining together of two compounds (usually a protein and polysaccharide) to make a vaccine more effective.


  • Demographic and Health Surveys (DHS): the DHS has implemented over 300 nationally-representative surveys in over 90 countries, asking questions about topics including fertility, family planning, maternal and child health (including vaccination), gender, HIV/AIDS, malaria, nutrition, and environmental health. The DHS is an amazing resource for epidemiologists and statisticians to understand the health profiles of many countries.
  • Diphtheria: A bacterial disease marked by the formation of a false membrane, especially in the throat, which can cause death.


  • Efficacy: A measure used to describe how good a vaccine is at preventing disease
  • Epidemic: The occurrence of disease within a specific geographical area or population that is in excess of what is normally expected
  • Endemic: The continual, low-level presence of disease in a community
  • Etiology: The cause of a disease
  • Exposure: Contact with infectious agents that promotes transmission


  • Haemophilus influenzae type b (Hib): A bacterial infection that may result in severe respiratory infections, including pneumonia, and other diseases such as meningitis. A vaccine for Hib is administered within 24 hours of birth.
  • Hepatitis A: A viral disease transmitted through ingestion of contaminated food or water, for which there is a vaccine.
  • Hepatitis B: A viral disease transmitted by infected blood or blood products, or through unprotected sex with someone who is infected, for which there is a vaccine.
  • Hepatitis C: is a liver disease caused by the Hepatitis C virus (HCV), which is found in the blood of persons who have the disease. HCV is spread by contact with the blood of an infected person, and a vaccine exists.
  • Hepatitis D: is a defective virus that needs the hepatitis B virus to exist. Hepatitis D virus (HDV) is found in the blood of persons infected with the virus.
  • Hepatitis E: is a virus (HEV) transmitted in much the same way as hepatitis A virus. Hepatitis E, however, does not often occur in the United States.
  • Herd immunity: See Community immunity.
  • Herpes Zoster (Shingles): A disease 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. Herpes Zoster is caused by the same virus that is responsible for chickenpox. After the primary infection (chickenpox), the virus becomes dormant, and in some, the virus reactivates years, or even decades, later and causes shingles.


  • 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 defense against them via the production of  antibodies to eliminate foreign organisms that invade the body.
  • 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 usually be determined with a laboratory test. See active and passive immunity.
  • Immunization (Vaccination, Inoculation): The process by which a person or animal becomes protected against a disease through a vaccination event.
  • Inactivated vaccine (killed vaccine): A vaccine made from viruses and bacteria that have been killed through physical or chemical processes. These killed organisms cannot cause disease, however the immune response from some inactivated vaccines may not last as long as that from attenuated vaccines.
  • Incidence: The number of new disease cases reported in a population over a certain period of time (incident rate of new disease infections).
  • Incubation period: The time between exposure incident and disease onset.
  • Influenza: A highly contagious viral infection characterized by sudden onset of fever, severe aches and pains, and inflammation of the mucous membrane. Influenza vaccinations vary year by year due to the significant genetic shift and drift that Influenza undergoes.


  • 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. Also known as an attenuated vaccine.


  • Measles: A contagious viral disease marked by a rash of red circular spots on the skin.
  • Memory Cell: A group of cells that help the body defend itself against disease by remembering prior exposure to specific organisms, so the 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. Meningitis can be bacterial, viral, or fungal.
  • Microbes: Tiny organisms (i.e. viruses and bacteria).


  • Outbreak: Sudden appearance of a disease in a specific geographic area (e.g. neighborhood or community) or population (e.g., adolescents, infants).


  • Pandemic: An epidemic occurring over a very large geographic area (often used interchangeably with epidemic).
  • Passive immunity: Protection against disease through antibodies produced by another human being or animal, i.e. maternal antibodies which are passed to the infant by the mother prior to birth. These antibodies temporarily protect the baby for the first 4-6 months of life. Passive immunity generally has limited effectiveness and diminishes over time (usually a few weeks or months).
  • Pathogens: Organisms (e.g. bacteria, viruses, parasites and fungi) that cause disease in human beings.
  • Pertussis (whooping cough): Bacterial infectious disease marked by a convulsive spasmodic cough, sometimes followed by a crowing intake of breath.
  • 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,  and rapid heart rate.
  • Poliomyelitis (polio): An acute infectious viral disease characterized by fever, paralysis, and atrophy of skeletal muscles. Polio is currently in the process of elimination worldwide, with only a few countries remaining with endemic infection.
  • Polysaccharide vaccines: Vaccines that are composed of long chains of sugar molecules that resemble the surface of certain types of bacteria. Polysaccharide vaccines exist for pneumococcal disease, meningococcal disease and Haemophilus Influenzae type b.
  • Prevalence: The number of disease cases (both new and existing) within a population over a given time period, i.e. all existing cases in a population at a time, not just newly occurring cases.


  • Rotavirus: A group of viruses that cause diarrhea in children.
  • Rubella: Viral infection that is milder than normal measles but as damaging to the fetus when it occurs early in pregnancy, leading to Congenital Rubella Syndrome.
  • RubeolaSee Measles.


  • Seroconversion: Development of antibodies in the blood of an individual who previously did not have detectable antibodies to a particular disease.
  • Shingles: See herpes zoster.
  • Smallpox (Variola)An acute, 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. Smallpox is the first and only disease to be eradicated through vaccination.
  • Strain: A specific version of an organism.
  • Subclinical infection: The presence of infection without symptoms.
  • Susceptible: Unprotected against disease with the potential to contract and spread.


  • Tetanus: Toxin-producing bacterial disease marked by painful muscle spasms. The tetanus vaccine is contained in TDap and DTap vaccinations.
  • ThimerosalThimerosal is a mercury-containing preservative used in some vaccines and other products since the 1930’s. While 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, in July 1999, the Public Health Service agencies, the American Academy of Pediatrics, and vaccine manufacturers agreed that thimerosal should be reduced or eliminated in vaccines as a precaution. Today, all routinely recommended childhood vaccines in the U.S. contain either no thimerosal or only trace amounts with the exception of some flu vaccines. There are thimerosal-free influenza vaccines available.
  • Typhoid Fever: Typhoid fever is a life-threatening diarrheal illness caused by the bacterium Salmonella Typhi. Persons with typhoid fever carry the bacteria in their bloodstream and intestinal tract.
  • Titer: The detection of antibodies in blood through a laboratory test which indicate immunity to a particular disease.


  • Vaccination: Injection of a killed or weakened infectious organism in order to prevent the disease.
  • Vaccine Adverse Event Reporting System (VAERS): A database managed by the CDC and the FDA. VAERS provides a mechanism for the collection and analysis of adverse events associated with vaccines currently licensed in the United States. Reports to VAERS can be made by the vaccine manufacturer, recipient, their parent/guardian or health care provider.
  • Vaccine Hesitancy: Vaccine hesitancy is defined as the WHO by the “delay in acceptance or refusal of vaccines despite availability of vaccination services. Vaccine hesitancy is complex and context specific varying across time, place and vaccines. It includes factors such as complacency, convenience and confidence.”
  • Vaccine Safety Datalink Project (VSD): In order to increase knowledge about vaccine adverse events, the CDC have formed partnerships with eight large Health Management Organizations (HMOs) to continually evaluate vaccine safety. The project contains data on more than 6 million people.
  • Varicella(Chickenpox) — An acute contagious disease characterized by papular and vesicular lesions which can develop into shingles later in life.
  • Variola: See smallpox.
  • 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. More and more, it seems that many vaccines do suffer from waning immunity, such as mumps vaccine and pertussis vaccination.
  • Whooping Cough: See Pertussis.
  • World Health Organization (WHO)The WHO is an international health organization whose core function is to “direct and coordinate international health work through collaboration.” WHO partners with countries, the United Nations system, international organizations, civil society, foundations, academia, and research institutions to improve health worldwide. WHO is headquartered in Geneva, Switzerland.

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