Influenza A and B are the two types of influenza viruses that cause epidemic human disease. Influenza B viruses currently circulating are divided into two antigenically and genetically distinct groups: the Victoria and Yamagata lineages.Influenza virus B is a genus in the virus family Orthomyxoviridae. A limited host range means that Influenza virus B pandemics are rare.
The nucleoprotein protects the negative strand viral RNA from nucleases by encapsidating it. encapsidated genomic RNA is termed the ribonucleoprotein (RNP) and serves as template for transcription and replication.