Influenzavirus B
（重定向自Influenza B virus）
Influenzavirus B is a genus in the virus family Orthomyxoviridae. The only species in this genus is called Influenza B virus.
Influenza B viruses are only known to infect humans and seals, giving them influenza. This limited host and range is apparently responsible for the lack of Influenzavirus B-caused influenza pandemics in contrast with those caused by the morphologically similar Influenzavirus A as both mutate by both antigenic drift and reassortment.