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Review
. 2022 Jan 12;10(1):112.
doi: 10.3390/vaccines10010112.

Subtype H3N2 Influenza A Viruses: An Unmet Challenge in the Western Pacific

Min Kang  1   2 , Mark Zanin  3   4 , Sook-San Wong  3   4
Affiliations
Review

Subtype H3N2 Influenza A Viruses: An Unmet Challenge in the Western Pacific

Min Kang et al. Vaccines (Basel). .

Abstract

Subtype H3N2 influenza A viruses (A(H3N2)) have been the dominant strain in some countries in the Western Pacific region since the 2009 influenza A(H1N1) pandemic. Vaccination is the most effective way to prevent influenza; however, low vaccine effectiveness has been reported in some influenza seasons, especially for A(H3N2). Antigenic mismatch introduced by egg-adaptation during vaccine production between the vaccine and circulating viral stains is one of the reasons for low vaccine effectiveness. Here we review the extent of this phenomenon, the underlying molecular mechanisms and discuss recent strategies to ameliorate this, including new vaccine platforms that may provide better protection and should be considered to reduce the impact of A(H3N2) in the Western Pacific region.

Keywords: egg-adaptation; influenza A(H3N2); novel vaccine platforms; vaccine effectiveness; western pacific.

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Conflict of interest statement

S-S.W. and M.K. have received speakers’ honoraria from Sanofi Pasteur (China).

Figures

Figure 1
Figure 1
Map of the influenza transmission zones as defined by the WHO. The Western Pacific countries are indicated in dark red. Inset labels the six countries where A(H3N2) were the dominant strain from 2010 week 21 to 2020 week 20. Map downloaded and modified from: https://www.atlasofms.org/map/china/country-classification/who-region# (accessed on 25 November 2021).
Figure 2
Figure 2
Number of influenza-positive specimens by type and subtype reported in six countries of the Western Pacific region in which A(H3N2) was the dominant strain from 2010 week 21 to 2020 week 20. Specimens were collected in China (A), Japan (B), the Republic of Korea (C), Australia (D), Singapore (E) and Mongolia (F). Data Source: FluNet (www.who.int/flunet, accessed on 11 November 2021).
Figure 3
Figure 3
The vaccine effectiveness (VE) against laboratory-confirmed influenza from 2011–2020 in the US by (A) strains and (B) age against A(H3N2). Data represents the pooled estimates, and error bars represent 95% confidence intervals. Data was obtained from www.cdc.gov/flu/vaccines-work/, (accessed on 12 November 2021).
See this image and copyright information in PMC

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