Phylogenetic relationships of partial sequences (nucleotides 346 to 866) of the HA1 coding fragment for A(H3N2) viruses isolated in 2003–2004 in the UK and worldwide.

<p>Genetic groups where viruses from the UK clustered are highlighted in green (I) and red (II). Some branches were condensed for clarity purposes; adjacent legends indicate the country/region where the majority of viruses within a cluster were isolated and the number of viruses included. These clusters also included sporadic viruses from other countries which were not detailed. Sequences from reference viruses A/Panama/2007/99 and A/Fujian/411/2002 were included in the phylogeny. The ML phylogeny was rooted using A/Panama/2007/99 as an outgroup. Branch lengths are drawn to scale. Bootstrap values (>70%) are displayed on the nodes.