Seroepidemiological study of influenza A (H1N1) pdm09 virus following the 2009–2010 wave in Shandong Province, China

Abstract

Introduction: The aims of this study were to understand the geographic extent, risk factors, and attack rate of influenza A (H1N1) pdm09 virus (pH1N1) infection in Shandong Province China and to elucidate influencing factors. Methods: In January and March 2010, a cross-sectional seroprevalence survey of pH1N1 was carried out. Serum samples from 9022 participants in the survey were subjected to the hemagglutination inhibition assay. Results: Among the 9022 participants, the overall rate of seropositivity against pH1N1 was 22.6%. The weighted rate, adjusted for gender, age, and region, was estimated to be 18.7%. Among 8340 subjects who did not report previous vaccination, the rate was 16.7%, as compared to 50.9% among 682 subjects reporting previous vaccination (p < 0.001). Within the unvaccinated population, the rate of seropositivity among 16–24 and 6–15 y-old subjects was 31.8% and 29.9%, respectively, as compared to 9.6% among subjects aged ≥ 60 y (p < 0.001) and 23% in the 0–5 y age group (p < 0.001). Those aged 6–15 y and aged 16–24 y had higher odds of seropositivity than those aged 0–5 y (odds ratio 1.53 and 1.48, respectively). Conclusions: These study findings help enhance our understanding of pH1N1 epidemiology and provide valuable information for the vaccination strategy for the influenza season.

Keywords::

• Influenza A (H1N1) pdm09
• seropositive rate
• China

Declaration of interest: No conflict of interest to disclose. This study received a grant from the Scientific and Technological Projects of Shandong Province (2009GG10002054).