FIG 1.

Conserved terminal sequences of seasonal influenza viruses. All publicly available full-length sequences (in cDNA sense) of human influenza A(H3N2), A(H1N1), and influenza B viruses were aligned for each gene segment of interest [9,472 HA, 6,948 NA, and 3,635 M for A(H1N1); 6,745 HA, 6,363 NA, and 3,766 M for A(H3N2); and 3,055 HA and 2,034 NA for influenza B virus. Full-length sequences are defined as sequences that have complete coding regions). The heights of nucleotides at the 20 terminal positions at each end of each segment are representative of their relative frequencies at a specific position using the WebLogo application (35). Underlined nucleotides correspond to the primer binding regions.