Prevalence of antibodies against seasonal influenza A and B viruses during the 2009-2010 and 2010-2011 influenza seasons in residents of Pittsburgh, PA, USA.

: Seroprevalence of antibodies against influenza viruses from 1000 people between the ages of 0 to 90 years of age (100 samples for each decade of life) in the Pittsburgh, PA, USA was measured. One year removed from the outbreak of novel H1N1 influenza into the human population in the Northern Hemisphere and following the emergence of a new H3N2 influenza isolate, sera was collected to determine the hemagglutination-inhibition antibodies against influenza A/H1N1, A/H3N2, and B viruses representative of viruses in the vaccine used for the 2010-2011 influenza season. The seroprevalence of antibodies to influenza virus, A/California/7/2009 (H1N1), increased from the previously reported November 2009 samples and the samples collected at the end of the 2010 influenza season (June 2010) during the 2010-2011 season in all age groups, but people the under the age of 20 had the highest rise in the number of positive samples. The number of individuals positive for H1N1 stayed the same through the entire influenza season. In contrast, there were little to no positive serum samples against the H3N2 virus, A/Perth/16/2009, from samples collected during the 2009-2010 influenza season, however, titers against these viruses rose significantly during the early months of the 2010-2011 season with the highest number of positive samples detected in the very young and very old populations. However, these titers waned by May, 2011 in those over the age of 40. There was a rise in adults to the B/Brisbane/60/2008 influenza virus in adults in samples collected in October, 2010, but these titers quickly declined. The highest titers to B influenza were detected in people between the ages of 10-30 years of age. These findings may have implications for the development of vaccination strategies aiming at the protection against seasonal and/or pandemic influenza virus infection and pre-pandemic preparedness activities.