Influenza B virus, like influenza A, belongs to the Orthomyxoviridae family and causes respiratory infections in humans. In contrast to influenza A, influenza B viruses are not classified into subtypes but are further categorized based on their lineage – Victoria or Yamagata. Influenza B viruses have a segmented RNA genome and share similar structures with influenza A, including the surface proteins hemagglutinin (HA) and neuraminidase (NA). Influenza B infections generally cause milder illness compared to influenza A, but they still contribute to seasonal flu outbreaks. The virus is transmitted through respiratory droplets, and symptoms typically include fever, cough, sore throat, and fatigue. Influenza B infections can occur in individuals of all ages, with a higher burden often observed in children. Vaccination plays a critical role in preventing influenza B infections and reducing the severity of illness. The trivalent influenza vaccine includes components targeting two influenza A subtypes (H1N1 and H3N2) and one influenza B lineage, while the quadrivalent vaccine includes both Victoria and Yamagata influenza B lineages. The selection of the influenza B lineage for inclusion in the vaccine is based on surveillance data to predict the predominant circulating strains for the upcoming flu season. Despite the challenges of antigenic variation, vaccination remains a key public health measure to control influenza B. Annual vaccination campaigns aim to achieve high vaccination coverage, particularly among vulnerable populations, to reduce the impact of influenza B on global public health.