What is virus strain?

Some articles on virus, virus strain:

ACAM-FLU-A
... given year to protect against the highly variable influenza virus ... influenza vaccine contains three influenza viruses one influenza type A subtype H3N2 virus strain, one influenza type A subtype H1N1 (seasonal) virus strain, and ...

Famous quotes containing the words strain and/or virus:

    And but for fancies, which aver
    That all thy motions gently pass
    Athwart a plane of molten glass,
    I scarce could brook the strain and stir
    Alfred Tennyson (1809–1892)

    Freedom is the most contagious virus known to man.
    Hubert H. Humphrey (1911–1978)