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Please cite this paper as: Yang et al. (2011) Seroprevalence of pandemic (H1N1) 2009 influenza and effectiveness of 2010/2011 influenza vaccine during 2010/2011 season in Beijing, China. Influenza and Other Respiratory Viruses 6(6), 381-388. Background In the post-pandemic period, pandemic (H1N1) 2009 virus was expected to circulate seasonally and was introduced into trivalent influenza vaccine during 2010/2011 season in the Northern Hemisphere. Objectives The aim of this study was to examine the evolution of herd immunity against pandemic (H1N1) 2009 virus in Beijing, China, during 2010/2011 season and effectiveness of the 2010/2011 trivalent vaccine. Methods Two serological surveys were conducted before and after 2010/2011 season in Beijing. A case-control study was used to investigate vaccine effectiveness against influenza-like illness (ILI) and lower respiratory tract infection (LRI). Results A total of 4509 and 4543 subjects participated in the pre- and post-season surveys, respectively. The standardized seroprevalence of pandemic (H1N1) 2009 influenza increased from 22·1% pre-season to 24·3% post-season ( P < 0·001). Significant elevation in seroprevalence appeared in the ≥60 years age-group ( P < 0·001), but not in others. The 2010/2011 trivalent vaccine contributed to the higher post-seasonal seroprevalence in unvaccinated individuals ( P = 0·024), but not in those vaccinated with monovalent pandemic vaccine ( P = 0·205), as well as in those without prior immunity versus those with immunity. The adjusted effectiveness of the 2010/2011 trivalent vaccine was 79% protection against ILI (95% CI, 61-89%) and 95% against LRI (95% CI: 59-99%). Conclusions A slight increase in herd immunity against pandemic (H1N1) 2009 influenza was observed in Beijing, China, during the 2010/2011 season. Prior vaccination and immunity had a suppressive impact on immune response toward this novel influenza virus, elicited by 2010/2011 trivalent vaccine. This trivalent vaccine conferred good protection against ILI and LRI. [ABSTRACT FROM AUTHOR]

Please cite this paper as: Wang et al. (2010) Emergency surveillance of influenza during 2009 in the Chinese city of Qingdao. Influenza and Other Respiratory Viruses 5(1), 53-59. In April, 2009, a new influenza pandemic caused by a swine-origin H1N1 subtype influenza virus was imminent. We thereby carried out an emergency surveillance study in a Chinese city of Qingdao. Pharyngeal swab samples were collected from four targeted groups and tested by reverse-transcription polymerase chain reaction. Each laboratory-confirmed pandemic H1N1 case or cluster was investigated, and the hemagglutinin genes of some of the viruses were sequenced and analyzed. A total of 140 pandemic H1N1 cases including 92 from 7 clusters were identified in the four targeted groups. None of them developed into severe infections. Meanwhile, 103 cases of seasonal influenza (98 H3N2 and 5 H1N1) and 10 clusters of seasonal H3N2 influenza were also identified. Among them, 38 pandemic H1N1 and two seasonal H3N2 influenza cases were air travellers, suggesting that air travel facilitates the spread of pandemic and seasonal influenza even in the northern hemisphere summer. In addition, it was found that pandemic H1N1 and seasonal H3N2 influenza viruses co-circulated in two clusters. No significant mutations were found in the hemagglutinin gene sequences of pandemic H1N1 viruses, but the seasonal H3N2 influenza viruses have become genetically distinguishable from those circulating in 2007-2008. [ABSTRACT FROM AUTHOR]

Please cite this paper as: Huai et al. (2010) A primary school outbreak of pandemic 2009 influenza A (H1N1) in China. Influenza and Other Respiratory Viruses DOI: 10.1111/j.1750-2659.2010.00150.x. Background We investigated the first known outbreak of pandemic 2009 influenza A (H1N1) at a primary school in China. Objectives To describe epidemiologic findings, identify risk factors associated with 2009 H1N1 illness, and inform national policy including school outbreak control and surveillance strategies. Methods We conducted retrospective case finding by reviewing the school’s absentee log and retrieving medical records. Enhanced surveillance was implemented by requiring physicians to report any influenza-like illness (ILI) cases to public health authorities. A case–control study was conducted to detect potential risk factors for 2009 H1N1 illness. A questionnaire was administered to 50 confirmed cases and 197 age-, gender-, and location-matched controls randomly selected from student and population registries. Results The attack rate was 4% (50/1314), and children from all grades were affected. When compared with controls, confirmed cases were more likely to have been exposed to persons with respiratory illness either in the home or classroom within 7 days of symptom onset (OR, 4·5, 95% CI: 1·9–10·7). No cases reported travel or contact with persons who had traveled outside of the country. Conclusions Findings in this outbreak investigation, including risk of illness associated with contacting persons with respiratory illness, are consistent with those reported by others for seasonal influenza and 2009 H1N1 outbreaks in school. The outbreak confirmed that community-level transmission of 2009 H1N1 virus was occurring in China and helped lead to changes in the national pandemic policy from containment to mitigation. [ABSTRACT FROM AUTHOR]