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Epidemiological and virological characteristics of influenza B: results of the global influenza B study.

Caini, S., Sue Huang, Q., Ciblak, M.A., Kusznierz, G., Owen, R., Wangchuk, S., Henriques, C.M.P., Njouom, R., Fasce, R.A., Yu, H., Feng, L., Zambon, M., Clara, A.W., Kosasih, H., Puzelli, S., Kasjo, H.A., Emukule, G., Hereaud, J.M., Ang, L.W., Venter, M., Mironenko, A., Brammer, L., Mai, L.T.Q., Schellevis, F., Plotkin, S., Paget, J. Epidemiological and virological characteristics of influenza B: results of the global influenza B study. Influenza and Other Respiratory Viruses: 2015, 9(Sup. 1), 3-12
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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
26 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 226%, 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.