RESUMO
BACKGROUND: Pre-existing immunity in individuals is a determinant condition for epidemic dynamics. During the current influenza A (H1N1) virus pandemic, cross-reactivity of seasonal vaccines from the last years and previous contact with seasonal influenza viruses was suggested as the cause of low severity and low incidence of the disease in persons aged 50-65 years and with history of seasonal influenza vaccination. METHODS: We performed a detailed search and analysis of 74 previously reported H1 epitopes present in influenza A virus contained in seasonal vaccines applied in Mexico from 2004 to date and in sequences from Mexican isolates from 2003, as well as in the recent influenza A (H1N1) 2009, and calculated the epitope conservation among vaccine, seasonal and pandemic influenza A (H1N1) virus. RESULTS: H1 epitope sequence identity ranged from 61.53-100 %. Of the 74 epitopes previously reported, 31 (41.9%) were completely conserved among all sequences analyzed in this study, whereas 43 (58.1%) had changes in one or more amino acids. CONCLUSIONS: Our findings contribute to the estimatation of the degree of epitope conservation among H1 from vaccine virus strains as well as in the different viruses that circulate in the Mexican population. These results may provide new elements to consider for analysis of cross-immunity to influenza viruses including the novel influenza A (H1N1) 2009 pandemic virus.
