Glossary of Terms

Common terms that you may encounter on the site.


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A (9) | B (2) | C (2) | D (2) | E (6) | G (1) | H (2) | I (8) | K (1) | L (1) | M (2) | P (5) | R (1) | S (5) | T (4) | U (1) | V (6)

  • Adjuvant

    An agent added to some vaccines that enhances the immune system’s response to vaccine antigens. Adjuvants used in vaccines include aluminum salts and, in Canada and the European Union, squalene, which is a fish-oil derived material.

  • Adverse event

    A possible side effect resulting from a vaccination.

  • Antibody

    A protein generated by the immune system in response to the presence of a specific antigen. Antibodies attach to that antigen to help counter its effects.

  • Antigen

    A substance that provokes the immune system to generate antibodies against it.

  • Antigen-presenting cell

    A white blood cell that recognizes antigens, binds to them, ingests them, breaks them down, and then presents pieces of them to T cells.

  • Antigenic drift

    Change in the genetic makeup of a virus, especially an influenza virus, that leads to a new strain of the virus. Antigenic drift causes the virus’s outer surface to appear different to a host previously infected with the ancestor strain of the virus. Antibodies produced by previous infection with the ancestor strain cannot effectively fight the mutated virus, and disease often results.

  • Antigenic shift

    The process by which different influenza A viruses combine to result in a new subtype of virus. Antigenic shift may result in global disease spread, or pandemic, because humans will have few or no antibodies to fight the virus.

  • Antitoxin

    Antibody that neutralizes a toxin. Diphtheria antitoxin, for example, is derived from the blood of horses immunized with diphtheria toxin and is given, along with antibiotics, to treat patients with clinical diphtheria.

  • Attenuation

    The process of weakening a pathogen. Attenuation may be achieved in a variety of way: by exposing the pathogen to heat or chemicals, for example, or by passing the pathogens through a growth medium many times. The goal of attenuation in virology is to produce an antigen that is capable of stimulating an immune response, and thus creating immunity, but not causing disease.