The recent influenza pandemic of 2009/2010 caused by the Influenzavirus A (H1N1) pandemic showed a severity profile different from seasonal flu due to a significant percentage of severe and fatal cases occurred in young adults without comorbidity. The virulence of Influenzavirus A (H1N1) pandemic is the result of protein interaction complexes and is related essentially some viral genes. The aim of this study was to characterize the genes that encodes for the hemagglutinin (H1) and polymerase basic 2 (PB2) of Influenzavirus A (H1N1) pandemic recovered from patients with flu coming from the metropolitan mesoregion, Belém-PA. The sample size consisted of 87 random samples of both genders, the 0-96 years, with severe acute respiratory syndrome (SARS) without comorbidity reported from May 2009 to August 2010. The samples were isolated in MDCK cell, and analyzed by molecular biology techniques that comprised three main steps: a) viral RNA (vRNA) extraction from supernatant of infected cells; b) amplification of the vRNA by Polymerase Chain Reaction preceded by Reverse Transcription (RT-PCR) technique; c) complete sequencing of genes encoding H1 and PB2. Of 87 strains amplified by RT-PCR in 82 amplicons the acquisition and analysis of sequences for the HA gene was obtained, whereas in 81 amplicons viral sequences were obtained for the PB2 gene. The comparative analysis of the sequences obtained with the sequence of the vaccine strain (A/California/07/2009 (H1N1)) revealed amino acid substitutions in HA (P83S, D97N; S203T, D222G, and I321V Q293H) and PB2 (K340N, and K526R M631L) proteins any changes were, however not associated with hospitalization. At the level of substitution in HA, the D97N alone or associated with the S203T was detected more frequently in the first wave. Furthermore, the level of PB2, a substitution K526R was found in the majority of strains that circulated during the first wave, while the M631L was more evident in the second. The D222G substitution in HA was only found in cases of death. Finally, there was a tendency of changes in HA antigenic sites. Thus, the genetic and antigenic continuous surveillance of Influenzavirus A (H1N1) pdm in circulation, as well as the sharing of information is extremely important for the best possible recommendation for virus which are included in vaccine the composition thus avoiding higher risk of severe epidemics in the future.
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