ABSTRACT
Objective To investigate the immunological level against influenza A (H1N1)2009 in Beijing and provide evidence to evaluate the developing trend of the disease. Methods Between Nov. 27,2009 and Dec. 23,2009, subjects were randomly selected from patients in hospitals (infectious and respiratory diseases related departments were excluded) ,volunteers in blood donation center and healthy subjects attending the physical examination center. Questionnaire survey was conducted and serum samples were collected to detect the hemagglutination-inhibition (HI) antibody against influenza A(H1N1) 2009 virus. Results 856 subjects participated in this survey, and 127 showed positive HI antibody to this pandemic virus. The proportions of sero-positivity among 0-5 ,was no significant difference in the sero-positivity between males and females (P=0.693). The analysis, factors as age, acute respiratory symptoms and the rate of pandemic (H1N1) 2009 vaccination were significantly associated with sero-positivity of HI antibody to the influenza A (H1N1) 2009 virus. Conclusion Above 15% of the population in Beijing showed protective antibody against influenza A (H1N1) 2009 virus, indicating the development of immunological barrier to this disease had been formed, to some extent.