title: Seroprevalence of pandemic H1N1 antibody among health care workers in Hong Kong following receipt of monovalent 2009 H1N1 influenza vaccine.
abstract: BACKGROUND
  Healthcare workers in many countries are recommended to receive influenza vaccine to protect themselves as well as patients. A monovalent H1N1 vaccine became available in Hong Kong in December 2009 and around 10% of local healthcare workers had received the vaccine by February 2010.
  
  
  METHODS
  We conducted a cross-sectional study of the prevalence of antibody to pandemic (H1N1) 2009 among HCWs in Hong Kong in February-March 2010 following the first pandemic wave and the pH1N1 vaccination campaign. In this study we focus on the subset of healthcare workers who reported receipt of non-adjuvanted monovalent 2009 H1N1 vaccine (Panenza, Sanofi Pasteur). Sera collected from HCWs were tested for antibody against the pH1N1 virus by hemagglutination inhibition (HI) and viral neutralization (VN) assays.
  
  
  RESULTS
  We enrolled 703 HCWs. Among 104 HCWs who reported receipt of pH1N1 vaccine, 54% (95% confidence interval (CI): 44%-63%) had antibody titer ≥1∶40 by HI and 42% (95% CI: 33%-52%) had antibody titer ≥1∶40 by VN. The proportion of HCWs with antibody titer ≥1∶40 by HI and VN significantly decreased with age, and the proportion with antibody titer ≥1∶40 by VN was marginally significantly lower among HCWs who reported prior receipt of 2007-08 seasonal influenza vaccine (odds ratio: 0.43; 95% CI: 0.19-1.00). After adjustment for age, the effect of prior seasonal vaccine receipt was not statistically significant.
  
  
  CONCLUSIONS
  Our findings suggest that monovalent H1N1 vaccine may have had suboptimal immunogenicity in HCWs in Hong Kong. Larger studies are required to confirm whether influenza vaccine maintains high efficacy and effectiveness in HCWs.
authors.affiliation: Infectious Disease Epidemiology Group, School of Public Health, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhou
authors.forename: Diane M W
authors.initials: DM
authors.lastname: Ng
authors.forename: Wing-Hong
authors.initials: WH
authors.lastname: Seto
authors.forename: Dennis K M
authors.initials: DK
authors.lastname: Ip
authors.forename: Henry K H
authors.initials: HK
authors.lastname: Kwok
authors.forename: Edward S K
authors.initials: ES
authors.lastname: Ma
authors.forename: Sophia
authors.initials: S
authors.lastname: Ng
authors.forename: Lincoln L H
authors.initials: LL
authors.lastname: Lau
authors.forename: J S Malik
authors.initials: JS
authors.lastname: Peiris
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Cowling
mesh_terms: D000328:Adult; D000914:Antibodies, Viral / Q000097:blood*; D003430:Cross-Sectional Studies; D005260:Female; D006282:Health Personnel; D006385:Hemagglutination Inhibition Tests; D006723:Hong Kong / Q000453:epidemiology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology / Q000627:therapeutic use*; D007251:Influenza, Human / Q000453:epidemiology* / Q000517:prevention & control* / Q000821:virology; D008297:Male; D008875:Middle Aged; D009500:Neutralization Tests; D016273:Occupational Exposure; D058873:Pandemics; D016036:Seroepidemiologic Studies; D014611:Vaccination; D055815:Young Adult
chemical_list: D000914:Antibodies, Viral; D007252:Influenza Vaccines
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