| influenza virus |
any of a group of orthomyxoviruses that cause influenza, including at least three serotypes: Influenzavirus A, Influenzavirus B, and Influenzavirus C. Antigenic variants are classified on the basis of their surface antigens (hemagglutinin and neuraminidase) as H1N1, H2N2, etc. Serotype A viruses are subject to major antigenic changes (antigenic shifts) as well as minor gradual antigenic changes (antigenic drift) and cause the major pandemics. ...
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| influenza virus v. |
[USP] a killed virus vaccine, available as whole virion, subvirion, and purified-surface-antigen preparations. The composition of the vaccine is changed each year in response to antigenic shifts and changes in prevalence of influenza virus strains; the vaccine is trivalent, containing two influenza A virus strains and one influenza B virus strain. Annual immunization before November is recommended for high-risk individuals (persons over 65 years of age and persons with chronic disease).
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