Figure 2.

WHO recommendations on the composition of influenza vaccines from 1978-1979 to 2013-2014 for the northern hemisphere [16-18].

For influenza B viruses, orange-colored bars indicate B/Yamagata lineage viruses, blue-colored bars B/Victoria lineage viruses, and gray-colored bars influenza B viruses with unknown lineage.

^aA(H3N2) virus antigenically similar to the cell-propagated prototype virus A/Victoria/361/2011. ^bFor the quadrivalent influenza vaccines containing two influenza B viruses.