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WHO Recommends the Composition of Influenza Vaccines for the 2016–2017 Winter Season

The World Health Organization (WHO) holds technical consultations every year in February and September to recommend the viruses to be included in the composition of influenza vaccines to be used during the flu seasons in the Northern and Southern Hemispheres. In March 2016, it published its recommendations for the 2016-2017 winter season in the Northern Hemisphere.Influenza A(H1N1)pdm09 viruses, which were predominant in many countries, circulated alongside influenza A(H3N2) and B viruses from September 2015 to January 2016. The majority of A(H1N1)pdm09 viruses were antigenically similar to the A/California/7/2009 strain, despite the notable emergence of two new genetically distinct subclades (6B.1) and (6B.2) within clade 6B. Some recent A(H1N1)pdm09 viruses from subclades 6B.1 and 6B.2 showed poor reactivity with human sera collected from individuals who had received a vaccine targeting the A/California/7/2009 strain. A(H3N2) viruses were associated with outbreaks in some countries. The majority of recent viruses were antigenically related to the A/Hong Kong/4801/2014 strain belonging to subclade 3C.2a, propagated in cell culture.Influenza B viruses belonging to the B/Victoria/2/87 and B/Yamagata/16/88 lineages circulated concurrently, with a predominance of viruses from the B/Victoria/2/87 lineage in many countries. Most viruses of the B/Victoria/2/87 lineage were antigenically and genetically closely related to the B/Brisbane/60/2008 and B/Texas/2/2013 strains.The majority of recent B/Yamagata/16/88 lineage viruses were closely related antigenically and genetically to the B/Phuket/3073/2013 virus. Zoonotic influenza infections caused by other viruses remain limited. From September 22, 2015, to February 22, 2016, five human cases of A(H5N6) were reported by China. Two human cases of A(H5N1) were reported, one by Bangladesh and the other by China. During the same period, 44 human cases of A(H7N9) infection were reported by China, and six human cases of influenza A(H9N2)—one by Bangladesh and five by China—originating from two different lineages. Finally, three human cases of influenza A(H1N1)v were reported, including two in China and one in the U.S., as well as one case of influenza A(H3N2)v in the U.S. Based on these considerations, the WHO has listed potential vaccine candidate viruses and reagents for vaccine standardization on its website.In France, the vaccines available for the 2016–2017 season are trivalent inactivated vaccines containing two influenza A virus strains: one A(H1N1) strain related to the A/California/7/2009 (H1N1)pdm09 virus and one A strain related to the A/Hong Kong/4801/2014 (H3N2), and one influenza B virus strain related to the B/Brisbane/60/2008 virus.