Background Healthcare workers in lots of countries are recommended to receive influenza vaccine to protect themselves as well as patients. reported receipt of pH1N1 vaccine, 54% (95% confidence interval (CI): 44%C63%) had antibody titer 140 by HI and 42% (95% CI: 33%C52%) had antibody titer 140 by VN. The proportion of HCWs with antibody titer 140 by HI and VN significantly decreased with age, and the proportion with antibody titer 140 by VN was marginally significantly lower among HCWs who reported prior receipt of 2007C08 seasonal influenza vaccine (odds ratio: 0.43; 95% CI: 0.19C1.00). After adjustment for age, the effect of prior seasonal vaccine receipt had not been significant statistically. Conclusions Our results claim that monovalent H1N1 vaccine may have had suboptimal immunogenicity in HCWs in Hong Kong. Bigger research must confirm whether influenza vaccine maintains high performance and effectiveness in HCWs. Introduction In ’09 2009 the 1st influenza pandemic from the 21st Hundred years was connected with a book influenza A(H1N1) disease that surfaced in THE UNITED STATES and rapidly pass on all over the world . In Hong Kong, on Apr 30 the 1st brought in pH1N1 case found its way to Hong Kong, 2009. In Sept and had subsided by November  Activity of pH1N1 peaked locally. pH1N1 was a notifiable condition through the entire first influx and 36,000 laboratory-confirmed instances had been notified including 1,400 HCWs, from an area human population of 7 million including 150,000 HCWs C. Vaccination is recognized as the very best precautionary measure and some studies discovered that one dosage in adults and two dosages in kids of monovalent pH1N1 vaccine had been sufficient to create seroprotective degrees of antibody against pH1N1 C. The Hong Kong authorities bought 3 million dosages from the Panenza monovalent pH1N1 vaccine produced by Sanofi Pasteur, that was the just pH1N1 vaccine formulation found in Hong Kong. Regional wellness authorities began to administer the vaccine to people of five target groups including HCWs from December 21, 2009, and extended the vaccination campaign to the general community in January 2010 . We conducted a cross-sectional study of the seroprevalence of pH1N1 antibody among HCWs in Hong Kong following the first epidemic wave. In a separate study we investigated antibody seroprevalence in HCWs who reported that they had not received pH1N1 vaccine . In this study we focus on HCWs who reported receipt of pH1N1 vaccine and investigate factors associated with antibody seroprevalence following vaccination. Methods Study design We recruited HCWs between February 11 and March 31, 2010 in 6 public hospitals comprising the Hong Kong West cluster of the local Hospital Authority, with a total workforce of around 7,000 HCWs in one acute care teaching hospital and five non-acute hospitals . We established fixed study locations in each TEF2 hospital, and participants were invited to participate in our study by open advertisement to all cluster employees. Some participants were approached for recruitment during their regular health check in the cluster staff clinic. HCWs were eligible to participate if they were Hong Kong residents and had worked in the cluster for at least one month. Subjects provided 3 ml of clotted blood, and other information including subject characteristics, history of exposure to influenza infection, and pandemic and seasonal vaccination history was collected by trained research assistants on a short questionnaire. The study protocol was approved GS-9190 by the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster. Written informed consent was obtained from all participants. Laboratory methods Serum samples GS-9190 were stored in a refrigerated container at 2C8C immediately after collection and delivered to the laboratory at the end of each working day for storage at ?70C prior to testing. Serum specimens were tested for antibody responses to A/California/04/2009 (H1N1) by hemagglutination inhibition (HI) and viral microneutralization (VN) assays using standard methods as previously described , , . The hemagglutination inhibition (HI) test was carried out in 96 well microtitre plates using reagents provided by Globe Health Corporation (WHO) Collaborating Center for Research and Study on Influenza Melbourne or the WHO Collaborating Center, Centres of Disease Control, GS-9190 Atlanta, GA using regular methods as comprehensive in the WHO GS-9190 reagent package and somewhere else. The pandemic H1N1 HA antigen had not been contained in the WHO reagent package and was made by tradition of A/California/04/2009 (H1N1) disease in MDCK cells. The traditional neutralization check for the A/California/04/2009 was completed in micro-titre plates using neutralization of disease cytopathogenic impact (CPE) in Madin-Darby Dog Kidney (MDCK) cells. Serial serum dilutions in quadruplicate had been blended with 100 cells tradition infectious dosage 50 (TCID50) for 2 hours and put into MDCK cells. 1 hour after disease, serum-virus mixtures had been eliminated and serum free of charge MEM with 2 ug/ml trypsin was put into.