The HA gene of the influenza H3N2 strains from the 1999-2000 season formed a phylogenetic subclade to A/ Moscow/10/99(H3N2) and A/Sydney/5/97(H3N2) (represented by A/Memphis/31/98) (Figure 2 ), located between A/Moscow/10/99 and A/Panama/2007/99 (not shown). The antigenicity of these strains was A/Moscow/ 10/99(H3N2)-like in a haemagglutination inhibition assay, and will therefore be referred to as Moscow-like throughout this report. The NA and the internal genes were all A/Moscow/10/99(H3N2)-like, with the exception of the matrix (M) gene that clustered as a subclade to the A/New York/55/01-like strains ( Figure 3 ). Figure 1 ). Thirteen isolates from this season were available for sequencing, and all were of the H1N1 subtype. These sequences represented two different co-circulating lineages (Figure 4 ). Lineage I is A/Bayern/7/ 95(H1N1)-like and lineage II include the H1N1 strains of today and the A/New Caledonia/20/99(H1N1) vaccine reference strain (Figure 4 ). The phylogenetic trees of NA and the internal genes showed the same topology ( Figure  3 and 4) . The lineage II strains are characterised by a deletion K130 in HA (K134 in H3 numbering) ( Table 1) 