Characteristic Analysis of the Epidemic Influenza Viruses in Niigata Prefecture,

Japan in 2012/13 and 2013/14 Seasons

Chika Hirokawa, Kaori Watanabe, Takashi Tazawa, Miwako Kato and Tsutomu Tamura

Influenza virus isolated in Niigata prefecture during 2012/13 and 2013/14 seasons were analyzed for the antigenic properties, genetic

variation and drug resistance with epidemics influenza. The 2012/13 season’s influenza epidemic in Niigata prefecture was caused mainly by

subtype A/H3 and to a lesser extent by type B Yamagata lineage. The epidemic of influenza in 2013/14 season started later than the 2012/13

season and was caused by a mix of subtype A/H1pdm09, subtype A/H3, type B Yamagata and Victoria lineages. Twenty-seven isolates in

Niigata prefecture tested in National Institute of Infectious Diseases were similar to each vaccine strain in the HA antigenicity. In the

phylogenetic analysis of HA1 genes, 10 isolates of subtype A/H1pdm09 fell into clade 6. The most of subtype A/H3 isolates in 2012/13 season

and 2013/14 seasons fell into clade 3C.2 and clade 3C.3 respectively. Eight isolates of type B Yamagata lineage collected in 2 seasons were

divided into clade 2 and clade 3, and all 5 isolates of type B Yamagata lineage in 2012/13 season fell into clade 2. All 6 isolates of type B

Victoria lineage fell into clade 1A including B/Brisbane/60/2008 (2010/11 season Japan vaccine strain). Any mutations related to

neuraminidase inhibitor resistance were not found in 52 isolates by sequencing analysis of NA gene. These data will be useful for the prediction

and prevention of epidemic of seasonal influenza.

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