Which two strains of influenza B are currently in circulation?

The correct choice highlights the two currently circulating strains of influenza B, which are B/Yamagata and B/Victoria. Influenza B is classified into two primary lineages, known as the Yamagata lineage and the Victoria lineage. These lineages have distinct genetic characteristics that allow for targeted vaccine development and effectiveness.

The relevance of knowing these strains lies in vaccination strategies and public health measures. The composition of flu vaccines is updated annually to include these strains, ensuring better protection against the circulating variants during the flu season. By focusing on B/Yamagata and B/Victoria, health authorities can effectively monitor and respond to influenza B infections.

Other options, while they may relate to influenza, do not represent the currently recognized strains of influenza B. For example, H1N1 and H3N2 are subtypes of influenza A, distinct from the B lineages. Additionally, B/Yamaguchi and B/Yamashita do not correspond to recognized lineages of influenza B and are not part of the current circulating strains. The terms lineage-PB1 and lineage-PB2 do not pertain to recognized influenza strains but rather suggest segments of the influenza virus genome, further indicating their irrelevance to the current question about circulating strains