Author Contributions: Dr Murdoch 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: Murdoch, Chambers, Jennings, Stewart, Priest, Florkowski, Livesey, Camargo, Scragg.
Acquisition of data: Murdoch, Slow, Chambers, Jennings, Florkowski, Livesey.
Analysis and interpretation of data: Murdoch, Slow, Chambers, Jennings, Stewart, Priest, Florkowski, Livesey, Camargo, Scragg.
Drafting of the manuscript: Murdoch.
Critical revision of the manuscript for important intellectual content: Murdoch, Slow, Chambers, Jennings, Stewart, Priest, Florkowski, Livesey, Camargo, Scragg.
Statistical analysis: Murdoch, Stewart, Florkowski.
Obtained funding: Murdoch, Chambers, Priest, Scragg.
Administrative, technical, or material support: Murdoch, Slow, Jennings.
Study supervision: Murdoch, Chambers.
Conflict of Interest Disclosures: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported.
Funding/Support: The study was funded by the Health Research Council of New Zealand.
Role of the Sponsors: The Health Research Council of New Zealand was not involved in the design or conduct of the study; the collection, management, analysis, and interpretation of the data; or the preparation, review, or approval of the manuscript.
Online-Only Content: The Author Video Interview is available .
Additional Contributions: We thank research assistants, Karina Barney, BSc, Penelope Fleming, RN, Sarah Godfrey, RN and Kelly Watson, MA, for recruitment and follow-up of participants, and database manager Monica Johnstone, BSc (all from University of Otago, Christchurch). We thank John Lewis, PhD, Peter Elder, PhD, Patalee Mahagamasekera, PhD, and other staff from Canterbury Health Laboratories for 25-OHD, plasma calcium, and respiratory virus testing. We also thank the data and safety monitoring committee from the Health Research Council of New Zealand and Penny Hunt, MD, for specialist advice. The WURSS was kindly provided with permission from Bruce Barrett, MD, PhD, University of Wisconsin. Finally, we thank all participants in the study. Mss Barney, Fleming, Godfrey, Watson, and Johnstone were employed by the study grant; no others received compensation for their role in the study.