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former genus name for the viruses that cause influenza, now found to be two different genera, which were named influenzavirus A and influenzavirus B.
Influenzavirus B/In·flu·en·za·vi·rus B/ a genus of viruses of the family Orthomyxoviridae containing the agent of influenza B. See influenza virus, under virus.
a genus of viruses of the family Orthomyxoviridae containing the agent of influenza B. It affects only humans. It can cause epidemics, albeit not as severe as those caused by influenza A. Vaccination against influenza B is available. See also influenza.