Influenza B

The main flu (influenza) stains affecting humans are influenza type A strains and influenza type B strains. Both influenza A and B consist of a number of different strains that circulate across the world, with infections peaking each winter.

Strains
Influenza type B strains are classified into two lineages:
 * Yamagata
 * Victoria

Each of these can be classified further into subtypes and variants.

Pandemic flu
Influenza type B strains have not been known to cause pandemics; all pandemics traced have been influenza type A strains, including the Spanish flu (1918-1919), and the H1N1 swine flu (2009-2010) pandemics.

Influenza vaccines
Annual influenza vaccines protect against both groups of inflenza B, and many subtypes of inflenza A virus.

Learn more

 * Types of Inflenza - CDC