Lee, Vernon J.Tan, Chi HsienYap, JonathanCook, Alex R.Ting, Pei-JunLoh, Jin-PhangGao, QiuhanChen, Mark I.Kang, Wee LeeTan, Boon HuanTambyah, Paul A.2015-11-252015-11-251932-6203http://hdl.handle.net/1885/16715BACKGROUND 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.This work was supported by a Singapore Ministry of Defense funded operational research program. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.© 2011 Lee et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.femalehumansincidenceinfluenza a virus, h1n1 subtypeinfluenza vaccinesinfluenza, humanlaboratoriesmalemilitary personnelpandemicsreproducibility of resultsrisk factorssingaporetreatment outcomeyoung adulttropical climatevaccination2011-10-2810.1371/journal.pone.00265722015-12-09