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Vaccine Effectiveness Against Laboratory-confirmed Influenza in Healthy Young Children: A CaseControl Study

Kelly, Heath MPH*†; Jacoby, Peter MSc‡; Dixon, Gabriela A. MB BS‡; Carcione, Dale PhD§; Williams, Simon BSc¶; Moore, Hannah C. BSc(Hons), GradDipClinEpi‡; Smith, David W. MB BS¶∥**; Keil, Anthony D. MB BS††; Van Buynder, Paul MPH§‡‡; Richmond, Peter C. MB BS‡§§;; the WAIVE Study Team

Pediatric Infectious Disease Journal:
doi: 10.1097/INF.0b013e318201811c
Original Studies
Abstract

Background: The Western Australian Influenza Vaccine Effectiveness study commenced in 2008 to evaluate a new program to provide free influenza vaccine to all children aged 6 to 59 months. We aimed to assess the protective effect of inactivated influenza vaccination in these children.

Methods: We conducted a prospective case–control study in general practices and a hospital emergency department, testing all eligible patients for influenza and a range of other common respiratory viruses. Influenza vaccine effectiveness (VE) against laboratory-confirmed influenza was estimated with cases defined as children with an influenza-like illness who tested positive and controls as those with an influenza-like illness who tested negative for influenza virus. We calculated VE using the adjusted odds ratio from multivariate logistic regression. As a surrogate marker for adequate specimen collection, we explored the difference in VE point estimates defining controls as children in whom another respiratory virus was detected.

Results: A total of 75 children were enrolled from general practices and 214 through the emergency department, with 12 (27%) and 36 (17%), respectively, having laboratory-confirmed influenza. Using all the influenza-negative controls, the adjusted VE was 58% (95% confidence interval, 9–81). When controls were limited to those with another virus present, the adjusted VE was 68% (95% confidence interval, 26–86).

Conclusions: VE estimates were higher when controls included only those children with another respiratory virus detected. Testing for other common respiratory viruses enables the control group to be restricted to those for whom an adequate sample is likely.

Author Information

From the School of *Computer Science and Software Engineering, University of Western Australia, Perth, Western Australia, Australia; †Victorian Infectious Diseases Reference Laboratory, North Melbourne, Victoria, Australia; ‡Telethon Institute for Child Health Research, Centre for Child Health Research, University of Western Australia, Perth, Western Australia, Australia; §Communicable Disease Control Directorate, Department of Health, Perth, Western Australia, Australia; ¶PathWest Laboratory Medicine WA, Nedlands, Western Australia, Australia; ‖School of Biomedical, Biomolecular and Chemical Sciences, University of Western Australia, Perth, Western Australia, Australia; **School of Pathology and Laboratory Medicine, University of Western Australia, Perth, Western Australia, Australia; ††Department of Microbiology, PathWest Laboratory Medicine, Princess Margaret Hospital for Children, Perth, Western Australia, Australia; ‡‡School of Public Health, University of Western Australia, Perth, Western Australia, Australia; and §§School of Paediatrics and Child Health, University of Western Australia, Perth, Western Australia, Australia.

Accepted for publication August 11, 2010.

The Western Australian Influenza Vaccine Effectiveness (WAIVE) study team includes Revle Bangor-Jones, MB BS, Dale Carcione, PhD, Gabriela Dixon, MB BS, Paul Effler, MPH, Gary Geelhoed, MB BS, Marie Hobson, Peter Jacoby, Msc, Anthony Keil, MB BS, Heath Kelly, MPH, Alan Leeb, MB BCh, Hannah Moore, BSc, Larissa Rhind, Peter Richmond, PhD, Helen Shirley, David Smith, MB BS, Paul van Buynder, MPH, and Simon Williams, BSc.

Address for correspondence: Peter Jacoby, MSc, PO Box 855, West Perth, Western Australia 6872, Australia. E-mail: peterj@ichr.uwa.edu.au.

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© 2011 Lippincott Williams & Wilkins, Inc.