title: [A survey of levels of antibodies against influenza viruses in the population of Wuxi City].
abstract: OBJECTIVE
  To investigate levels of antibodies against type A and type C influenza viruses and those against the 2009 H1N1 influenza A virus (before and after the 2009 H1N1 pandemic) among residents in Wuxi. To compare levels of antibodies against the 2009 H1N1 influenza virus (one year after the pandemic) in the unvaccinated population with those in the population who received vaccine.
  
  
  METHODS
  Serum samples were collected from subjects (aged 1-60 years) during September 2008 to May 2009, and during September 2010 to January 2011. Also collected were serum samples from adults who had received vaccines for pandemic (H1N1) 2009 for one year. Antibody response to influenza viruses was measured using hemagglutination inhibition (HI) assay. Seropositivity rate, seroprotection rate and geometric mean titer (GMT) were compared for each age group during different periods.
  
  
  RESULTS
  Before the outbreak of the 2009 H1N1 pandemic, seropositivity rate, seroprotection rate and GMT among the study subjects in were 2.86% (4/140), 0.71% (1/140) and 5.23, respectively. One year after the outbreak, seropositivity rate, seroprotection rate and GMT among the study subjects were 66.33%, 37.76% and 19.17, respectively. Among them, adult subjects showed 50.00% seropositivity rate, 19.44% seroprotection rate and 13.09 GMT, while adult subjects who had received vaccine for one year showed 61.36% seropositivity rate, 22.73% seroprotection rate and 14.14 GMT. No significant difference was observed between these two populations (P > 0.05 for all three indexes). Furthermore, before the outbreak of the 2009 H1N1 pandemic, levels of antibodies against seasonal influenza viruses among the study subjects were as follows: for H1N1 virus, seropositivity rate, seroprotection rate and GMT were 55.00%, 35.00% and 16.90, respectively; for H3N2 virus, seropositivity rate, seroprotection rate and GMT were 86.40%, 84.30% and 58.56, respectively.
  
  
  CONCLUSIONS
  One year after the 2009 H1N1 influenza A virus had spread to Wuxi, the population levels of antibodies against this virus have approached those against seasonal influenza viruses, as reflected by seropositivity rates, seroproection rates and GMT. Moreover, considerable levels of antibodies against seasonal influenza viruses were observed in populations, indicating no seasonal influenza outbreak would occur recently.
authors.affiliation: Wuxi Center for Disease Control and Prevention, Wuxi 214023, China.
authors.forename: Feng-Xing
authors.initials: FX
authors.lastname: You
authors.forename: Na
authors.initials: N
authors.lastname: Sun
authors.forename: Guang-Yuan
authors.initials: GY
authors.lastname: Ma
authors.forename: Miao-Miao
authors.initials: MM
authors.lastname: Wang
authors.forename: Dan
authors.initials: D
authors.lastname: Sa
authors.forename: Chao
authors.initials: C
authors.lastname: Shi
authors.forename: Jia-Lin
authors.initials: JL
authors.lastname: Wu
authors.forename: Xia
authors.initials: X
authors.lastname: Lin
authors.forename: Yong
authors.initials: Y
authors.lastname: Xiao
authors.forename: Yan-Hua
authors.initials: YH
authors.lastname: Qian
authors.forename: Yong
authors.initials: Y
authors.lastname: Jiang
authors.forename: Jie
authors.initials: J
authors.lastname: Xie
authors.forename: Ya-Yong
authors.initials: YY
authors.lastname: Ji
authors.forename: Hong-Xia
authors.initials: HX
authors.lastname: Guan
mesh_terms: D000293:Adolescent; D000328:Adult; D000914:Antibodies, Viral / Q000097:blood* / Q000276:immunology; D002648:Child; D002675:Child, Preschool; D002681:China; D005260:Female; D006385:Hemagglutination Inhibition Tests; D006801:Humans; D007223:Infant; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000097:blood* / Q000276:immunology / Q000517:prevention & control / Q000821:virology; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines