Trivalent inactivated influenza vaccine effective against influenza A(H3N2) variant viruses in children during the 2014/15 season, Japan

Norio Sugaya,Shinichiro Sekiguchi,Makoto Yoshida,Kenichiro Tsunematsu,Michiko Myokai,Akihiro Sato,Yoshio Yamaguchi,Hiroaki Baba,Machiko Toki,Masayoshi Shinjoh,Yuji Nakata,Atsushi Narabayashi,Takahisa Kimiya,Ichiro Ookawara,Chiharu Kawakami,Keiko Mitamura,Motoko Fujino,Naoko Yoshida,Mio Kono,Osamu Komiyama,Haruhisa Fujita ,Nobuyuki Taguchi ,Masatoshi Ishikawa ,Tsuyoshi Takahashi

doi:10.2807/1560-7917.es.2016.21.42.30377

Abstract

The 2014/15 influenza season in Japan was characterised by predominant influenza A(H3N2) activity; 99% of influenza A viruses detected were A(H3N2). Subclade 3C.2a viruses were the major epidemic A(H3N2) viruses, and were genetically distinct from A/New York/39/2012(H3N2) of 2014/15 vaccine strain in Japan, which was classified as clade 3C.1. We assessed vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in children aged 6 months to 15 years by test-negative case–control design based on influenza rapid diagnostic test. Between November 2014 and March 2015, a total of 3,752 children were enrolled: 1,633 tested positive for influenza A and 42 for influenza B, and 2,077 tested negative. Adjusted VE was 38% (95% confidence intervals (CI): 28 to 46) against influenza virus infection overall, 37% (95% CI: 27 to 45) against influenza A, and 47% (95% CI: -2 to 73) against influenza B. However, IIV was not statistically significantly effective against influenza A in infants aged 6 to 11 months or adolescents aged 13 to 15 years. VE in preventing hospitalisation for influenza A infection was 55% (95% CI: 42 to 64). Trivalent IIV that included A/New York/39/2012(H3N2) was effective against drifted influenza A(H3N2) virus, although vaccine mismatch resulted in low VE.

Highlights

Influenza vaccination is the most effective method of preventing influenza virus infection and its potentially severe complications
Trivalent inactivated influenza vaccine (IIV) was approved for use in children in Japan until the 2014/15 season, and we have previously reported on the vaccine effectiveness (VE) of IIV in children in Japan based on the results of influenza rapid diagnostic tests (IRDT) during the 2013/14 season [14], when influenza A(H1N1)pdm09 and B viruses were the main epidemic strains
The HA sequences of the majority of the 128 influenza A(H3N2) viruses in the 2014/15 season that were sequenced (113/128; 88.3%) were further characterised within this clade as belonging to subclade 3C.2a of clade 3C.2, with fewer (15/128; 11.7%) belonging to clade 3C.3 (Figure 1). These subclade 3C.2a viruses are considered genetically distinct from both the A/New York/39/2012 (H3N2) clade 3C.1 vaccine strain used in Japan and the A/Texas/50/2012 WHO vaccine reference strain

Summary

Introduction

Influenza vaccination is the most effective method of preventing influenza virus infection and its potentially severe complications. Based on the results of randomised controlled trials [1,2] and observational studies [3,4] the vaccine effectiveness (VE) of inactivated influenza vaccine (IIV) in healthy children has been reported to be 40% to 70%. In 2014, it was clearly recommended in the US that live attenuated influenza vaccine (LAIV) be used in healthy children from 2 to 8 years of age [8]. One large randomised trial reported superior relative efficacy of LAIV over IIV against antigenically drifted influenza A(H3N2) viruses [11], neither LAIV nor IIV provided significant protection against the drifted influenza A(H3N2) viruses in children in the 2014/15 season, and LAIV did not provide greater protection than IIV against these viruses [8]. LAIV is no longer recommended over IIV in children aged 2–8 years in the US [12]

Methods

Results

Conclusion