Severity of the two post-pandemic influenza seasons 2010-11 and 2011-12 in Northern Greece.

Since the pandemic in 2009, the two following post pandemic influenza seasons have been associated with increased morbidity and mortality rates in Northern Greece. The scope of this short report is to provide relevant epidemiological information, an evaluation of the efficacy of the seasonal vaccine and antiviral drugs. Molecular analysis revealed the close match of A(H1N1) 2009 pandemic and post-pandemic 2010-11 viruses with the vaccine virus. However, a proportion of the influenza A(H3N2) and B viruses that circulated in 2011-12 differed from the vaccine strains, possibly explaining the high hospitalization and fatality rates. There is also a trend of new virus strains to accumulate amino acid changes. Only A(H1N1) viruses resistant to oseltamivir have been detected. Constant epidemiological and molecular surveillance is essential to monitor the efficacy of the vaccine and antiviral drugs and assess the severity of each influenza season.