title: Effectiveness of pandemic H1N1-2009 vaccination in reducing laboratory confirmed influenza infections among military recruits in tropical Singapore.
abstract: BACKGROUND
  Limited information is available about pandemic H1N1-2009 influenza vaccine effectiveness in tropical communities. We studied the effectiveness of a pandemic H1N1 vaccination program in reducing influenza cases in Singapore.
  
  
  METHODS
  A surveillance study was conducted among military personnel presenting with febrile respiratory illness from mid-2009 to mid-2010. Consenting individuals underwent nasal washes, which were tested with RT-PCR and subtyped. A vaccination program (inactivated monovalent Panvax H1N1-2009 vaccine) was carried out among recruits. A Bayesian hierarchical model was used to quantify relative risks in the pre- and post-vaccination periods. An autoregressive generalised linear model (GLM) was developed to minimise confounding.
  
  
  RESULTS
  Of 2858 participants, 437 (15.3%), 60 (2.1%), and 273 (9.6%) had pandemic H1N1, H3N2, and influenza B. The ratio of relative risks for pandemic H1N1 infection before and after vaccination for the recruit camp relative to other camps was 0.14 (0.016,0.49); for H3N2, 0.44 (0.035,1.8); and for influenza B, 18 (0.77,89). Using the GLM for the recruit camp, post-vaccination weekly cases decreased by 54% (37%,67%, p<0.001) from that expected without vaccination; influenza B increased by 66 times (9-479 times, p<0.001); with no statistical difference for H3N2 (p = 0.54).
  
  
  CONCLUSIONS
  Pandemic vaccination reduced H1N1-2009 disease burden among military recruits. Routine seasonal influenza vaccination should be considered.
authors: Biodefence Centre, Ministry of Defence, Singapore, Singapore. vernonljm@hotmail.com
authors: Vernon J
authors: VJ
authors: Lee
authors: Chi Hsien
authors: CH
authors: Tan
authors: Jonathan
authors: J
authors: Yap
authors: Alex R
authors: AR
authors: Cook
authors: Pei-Jun
authors: PJ
authors: Ting
authors: Jin-Phang
authors: JP
authors: Loh
authors: Qiuhan
authors: Q
authors: Gao
authors: Mark I
authors: MI
authors: Chen
authors: Wee Lee
authors: WL
authors: Kang
authors: Boon Huan
authors: BH
authors: Tan
authors: Paul A
authors: PA
authors: Tambyah
mesh_terms: D005260:Female; D006801:Humans; D015994:Incidence; D053118:Influenza A Virus, H1N1 Subtype / Q000276:immunology*; D007252:Influenza Vaccines / Q000276:immunology; D007251:Influenza, Human / Q000453:epidemiology* / Q000276:immunology / Q000517:prevention & control* / Q000821:virology; D007753:Laboratories; D008297:Male; D008889:Military Personnel / Q000706:statistics & numerical data*; D058873:Pandemics / Q000517:prevention & control*; D015203:Reproducibility of Results; D012307:Risk Factors; D012846:Singapore / Q000453:epidemiology; D016896:Treatment Outcome; D014329:Tropical Climate; D014611:Vaccination; D055815:Young Adult
chemical_list: D007252:Influenza Vaccines; C551358:panvax