Antibody prevalence to the 2009 pandemic influenza A (H1N1) virus in Germany: geographically variable immunity in winter 2010/2011.

Location- and age-specific prevalence of antibodies against 2009 pandemic influenza A (H1N1) virus were determined in sera of blood donors collected during winter 2010/2011 in Germany. Prevalence of antibodies at protective titres (HI ≥1:40) varied significantly between cities (24.13-83.67 %) throughout all age groups. However, high level antibodies (HI >1:80) were most prevalent among young individuals (18-29 and 30-39 years). Overall, this study demonstrates that older people (50-59 and 60-70 years) are no longer more likely to present protective antibody titres against 2009 pandemic influenza A (H1N1) virus than younger individuals. Furthermore, our data show a highly variable immunity among the German population in different major cities almost 2 years after the detection of first cases in Germany.