ing sequences were aligned with MAFFT (using L-INS-I settings [21] ) and the resulting multiple alignment was visualized and annotated in Jalview [22] . A neighbour joining tree with pairwise gap deletion, Poisson correction as distance measure and 500 bootstrap replicates (generated with MEGA [23] ) produces robust groupings consistent with previous studies [24] for the known NA subtypes (clustering of N1, N4, N5+N8 on one side and N2, N3, N6+N7+N9 on the other) and reliably places the new NA with other N1s. Interestingly, inside the N1 cluster, the new NA appeared close to the N1 of H5N1 avian flu viruses. The alignment and corresponding phylogenetic tree are available at http://mendel.bii.a-star.edu.sg/ SEQUENCES/H1N1/.