Author Contributions: Dr Chen had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study concept and design: Chen, Lee, R. T. P. Lin, Yap, Chow, Chia.
Acquisition of data: Chen, Lee, Lim, R. T. P. Lin, Koh, Yap, L. W. L. Tan, B. H. Tan, Loh, Durrant, Chia.
Analysis and interpretation of data: Chen, Lee, R. T. P. Lin, Koh, Yap, C. Lin, Cook, Laurie, Shaw, Chow, Kelso, Chia.
Drafting of the manuscript: Chen, Lee, Koh, Yap, C. Lin.
Critical revision of the manuscript for important intellectual content: Chen, Lim, R. T. P. Lin, Koh, Yap, Cook, Laurie, L. W. L. Tan, B. H. Tan, Loh, Shaw, Durrant, Chow, Kelso, Chia.
Statistical analysis: Chen, Lee, Yap, Cook
Obtained funding: Chen, Lee, Lim, R. T. P. Lin, Yap, B. H. Tan, Loh, Chow.
Administrative, technical, or material support: Chen, Lee, Lim, R. T. P. Lin, Yap, C. Lin, Laurie, L. W. L. Tan, B. H. Tan, Loh, Shaw, Durrant, Chow, Kelso, Chia.
Study supervision: Chen, Lee, R. T. P. Lin, Yap, Chia.
Financial Disclosures: Dr Cook reported that he has received research funding from the National University of Singapore. Dr Lee reported that he has received unrelated research funding from GlaxoSmithKline. No other financial disclosures were reported.
Funding/Support: This project was funded by grant NMRC/H1N1O/005/2009 from the National Medical Research Council of Singapore. The Melbourne World Health Organization Collaborating Centre for Reference and Research on Influenza is supported by the Australian Government Department of Health and Ageing; the Centre has collaborative projects with vaccine companies unrelated to this study. The military cohort study was funded by the Ministry of Defence, Singapore.
Role of the Sponsor: None of the sponsors participated in the design and conduct of the study, in the collection, analysis, and interpretation of the data, or in the preparation, review, or approval of the manuscript.
Additional Contributions: We thank Pei Ling Loh, BSc, Nataline Tang, BSc, and Dollyn Quek, BSc, of the National Public Health Laboratory in Singapore, and Baldev Singh, AN, Caroline Lee, BSc, Jessie Tan, BSc, Rachelle Goh, RN, and Elaine Pek, MHSM, from the Infectious Disease Research Centre at Tan Tock Seng Hospital; Angela Cheong, BSc, from the National University of Singapore; Joshua Tay, MBBS, and Christine Gao, BSc, from the Singapore Armed Forces; and Janet Chew, BSc, from the DSO, National Laboratories, Singapore, for their contributions to this study. We thank the Communicable Diseases Division, Ministry of Health, Singapore, for contributing national surveillance data and other support during the conduct of the study. All individuals acknowledged here performed their roles as part of their regular duties and were not additionally compensated for their contributions.