INTRODUCTION Literature on influenza focuses on influenza A,
despite influenza B having a large public health impact. The
Global Influenza B Study aims to collect information on global
epidemiology and burden of disease of influenza B since 2000.
METHODS Twenty-six countries in the Southern (n = 5) and
Northern (n = 7) hemispheres and intertropical belt (n = 14)
provided virological and epidemiological data. We calculated the
proportion of influenza cases due to type B and Victoria and
Yamagata lineages in each country and season; tested the correlation
between proportion of influenza B and maximum weekly influenzalike
illness (ILI) rate during the same season; determined the
frequency of vaccine mismatches; and described the age distribution
of cases by virus type.
RESULTS The database included 935 673 influenza cases (2000–
2013). Overall median proportion of influenza B was 22 6%, with no statistically significant differences across seasons. During seasons
where influenza B was dominant or co-circulated (>20% of total
detections), Victoria and Yamagata lineages predominated during
64% and 36% of seasons, respectively, and a vaccine mismatch was
observed in 25% of seasons. Proportion of influenza B was inversely
correlated with maximum ILI rate in the same season in the Northern
and (with borderline significance) Southern hemispheres. Patients
infected with influenza B were usually younger (5–17 years) than
patients infected with influenza A.
CONCLUSION Influenza B is a common disease with some
epidemiological differences from influenza A. This should be
considered when optimizing control/prevention strategies in different
regions and reducing the global burden of disease due to influenza.