During the Northern Hemisphere winter of 2003ââ?¬â??2004 the emergence of a novel influenza antigenic variant, A/Fujian/411/\n2002-like(H3N2), was associated with an unusually high number of fatalities in children. Seventeen fatal cases in the UK were\nlaboratory confirmed for Fujian/411-like viruses. To look for phylogenetic patterns and genetic markers that might be\nassociated with increased virulence, sequencing and phylogenetic analysis of the whole genomes of 63 viruses isolated\nfrom fatal cases and non fatal ââ?¬Ë?ââ?¬Ë?controlââ?¬â?¢Ã¢â?¬â?¢ cases was undertaken. The analysis revealed the circulation of two main genetic\ngroups, I and II, both of which contained viruses from fatal cases. No associated amino acid substitutions could be linked\nwith an exclusive or higher occurrence in fatal cases. The Fujian/411-like viruses in genetic groups I and II completely\ndisplaced other A(H3N2) viruses, but they disappeared after 2004. This study shows that two A(H3N2) virus genotypes\ncirculated exclusively during the winter of 2003ââ?¬â??2004 in the UK and caused an unusually high number of deaths in children.\nHost factors related to immune state and differences in genetic background between patients may also play important roles\nin determining the outcome of an influenza infection.
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