A Comprehensive Analysis of the Influenza A/Hong Kong/2671/2019 IVR-208 (H3N2) Antigen (DB15704): From Molecular Standardization to Clinical Application in the COVID-19 Era

Executive Summary

The Influenza A virus A/Hong Kong/2671/2019 IVR-208 (H3N2) antigen, identified by DrugBank accession number DB15704, represents a critical component in the global strategy for seasonal influenza prevention, particularly during the 2020-2021 Northern Hemisphere and 2021 Southern Hemisphere influenza seasons. This report provides an exhaustive analysis of the antigen, from its virological origins and molecular characterization to its integration into commercial vaccines and its role in pioneering clinical research. Derived from an egg-propagated candidate vaccine virus, the antigen is inactivated, typically with formaldehyde for bulk production, and serves as the primary immunogen in numerous quadrivalent inactivated influenza vaccines (IIV4s). Its selection by the World Health Organization (WHO) was predicated on extensive global surveillance data from the 2019-2020 season, which indicated its antigenic relevance to circulating H3N2 strains.

This antigen's deployment occurred during a period of unprecedented global health disruption. The COVID-19 pandemic and the associated non-pharmaceutical interventions led to a historic suppression of influenza virus circulation worldwide. Consequently, traditional metrics of vaccine effectiveness for the 2020-2021 season could not be estimated. Despite this, the vaccination campaign, which included this H3N2 component, was a crucial public health measure aimed at mitigating the burden on healthcare systems already strained by the pandemic.