In the NA gene, it was showed that mutations V106I and N248D were present in samples at increasing numbers through early pandemic month (April to December 2009) [23] . We found both mutations at high percentages, 85.1% and 85.9% respectively, in our dataset. Change 106I was present in the 20th century cases of H1N1 (in 1918 [pandemic] , and 1977), as well as 248D (in 1977). Since residue at position 248 is located at the drug target domain (DTD) region, as residue 275, it could potentially affect the sensitivity to NA inhibitors. Another substitution of possible interest in NA sequences is D199N, which was previously associated with an increase in oseltamivir resistance in both seasonal and H5N1 virus strains [24] . We found, however, only 4 out of 1273 NA sequences (0.3%) containing this change. The rare substitution I223R, which was reported in association with resistance to oseltamivir, zanamivir, and peramivir [25] , was also found in only 2 out of 1273 NA sequences (0.2%). Substitution H275Y has been related to oseltamivir resistance, especially in immunocompromised or severely ill persons [26] . It was found, however, in sporadic cases in most of the countries at low frequencies (~1%) [27] . In our study, we found 2% of sequences containing this change.