A humoral immunity survey following the 2012 influenza season after the pH1N1 pandemic in Guangzhou, China.

According to pathogenic surveillance data during the first half of 2012, the H3N2 influenza virus was prevalent in Guangdong, China, but no pandemic H1N1 (pH1N1) virus was detected. This study aimed to measure the seroprevalence of pH1N1 and H3N2 infection following the influenza epidemic in 2012. We collected serum samples by stratified random sampling in a cross-sectional survey from August, 2012 to October, 2012. Antibody titers against H3N2, pH1N1, and influenza B antigens were measured by the hemagglutination inhibition (HI) assay, and age-specific seroprevalence and non-immunity were calculated. A total of 566 serum samples were collected from subjects who had not received an influenza vaccination. The seroprevalence of H3N2, pH1N1, and influenza B were 61.7%, 31.3%, and 40.4%, respectively, while non-immunity was calculated to be 9.2%, 40.6%, and 27.0%, respectively. The highest recorded seroprevalence was 86.0% for H3N2 in the 6-15 year age group, while the lowest was 14.6% for pH1N1 in the 60+ age group. Non-immunity fractions were 44.4% and 53.5% in the 0-6 and 60+ age groups, respectively. In conclusion, the seroprevalence of pH1N1 remained below 50% in all age groups following the 2012 influenza season. These data suggest that vaccination against pH1N1 antigens should be conducted, especially in the older age groups, before the next influenza season.