Identification of seasonal vaccine hemagglutinin subtype 1 (H1) epitopes in Mexican isolates of the new influenza A (H1N1) 2009 virus.

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.