Assessment of population susceptibility to upcoming seasonal influenza epidemic strain using interepidemic emerging influenza virus strains.

Lin-Lei Chen,Sidney Tam,Wai-Lan Wu,Xixia Ding,Kwok-Hung Chan,Kelvin K W To,Kwok-Yung Yuen,Jonathan D Ip,Anthony C K Ng,Lu Lu,Anna J X Zhang,Wan-Mui Chan,Jian-Piao Cai,Thrimendra K Dissanayake,Carol H Y Fong,Ivan F N Hung

doi:10.1017/s0950268819001717

Lin-Lei Chen, Sidney Tam + Show 14 more

Open Access

https://doi.org/10.1017/s0950268819001717

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Abstract

Seasonal influenza virus epidemics have a major impact on healthcare systems. Data on population susceptibility to emerging influenza virus strains during the interepidemic period can guide planning for resource allocation of an upcoming influenza season. This study sought to assess the population susceptibility to representative emerging influenza virus strains collected during the interepidemic period. The microneutralisation antibody titers (MN titers) of a human serum panel against representative emerging influenza strains collected during the interepidemic period before the 2018/2019 winter influenza season (H1N1-inter and H3N2-inter) were compared with those against influenza strains representative of previous epidemics (H1N1-pre and H3N2-pre). A multifaceted approach, incorporating both genetic and antigenic data, was used in selecting these representative influenza virus strains for the MN assay. A significantly higher proportion of individuals had a ⩾four-fold reduction in MN titers between H1N1-inter and H1N1-pre than that between H3N2-inter and H3N2-pre (28.5% (127/445) vs. 4.9% (22/445), P < 0.001). The geometric mean titer (GMT) of H1N1-inter was significantly lower than that of H1N1-pre (381 (95% CI 339-428) vs. 713 (95% CI 641-792), P < 0.001), while there was no significant difference in the GMT between H3N2-inter and H3N2-pre. Since A(H1N1) predominated the 2018-2019 winter influenza epidemic, our results corroborated the epidemic subtype.

Highlights

Seasonal influenza virus infection has been associated with an estimated 9.4 million respiratory hospitalisations and an estimated 0.3 to 0.6 million deaths per year globally [1, 2]
Log-transformed MN titers were used for the statistical analysis of the geometric mean titer (GMT) and 95% confidence interval (CI) as we described previously [23, 24]
Before the 2018/2019 winter influenza season, the last A(H1N1) epidemic occurred in the 2015/2016 winter influenza season

Summary

Introduction

Seasonal influenza virus infection has been associated with an estimated 9.4 million respiratory hospitalisations and an estimated 0.3 to 0.6 million deaths per year globally [1, 2]. Studies have shown that the median ages of patients with influenza A(H1N1) (20 years) and influenza B (16 years) virus infection are younger than those with influenza A(H3N2) (30 years) virus infection [7]. For influenza B virus, patients infected by the Victoria lineage are younger than those infected with the Yamagata lineage (median age: 20 years vs 40 years) [8]. Vaccine effectiveness is much lower for influenza A (H3N2) virus than influenza A(H1N1) or influenza B virus [10].

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