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Influenza vaccine effectiveness in general practice and in hospital patients in Victoria, 2011–2013

Heath A Kelly, Courtney Lane and Allen C Cheng
Med J Aust 2016; 204 (2): 76. || doi: 10.5694/mja15.01017

Summary

Objective: To compare influenza vaccine effectiveness in the general practice and hospital settings.

Design: Analysis of annual case test-negative studies.

Setting: Victorian sentinel hospitals and general practices, 2011–2013.

Participants: Patients presenting to general practitioners, or those admitted to hospital with an influenza-like illness who were tested for influenza using a polymerase chain reaction assay. Cases were patients with a positive test result for influenza; non-cases (controls) had a negative test result.

Main outcome measures: Vaccine effectiveness against laboratory-confirmed influenza.

Results: Hospitalised patients were on average older and reported a higher proportion of comorbidities than general practice patients. The pooled estimate of influenza vaccine effectiveness against laboratory-confirmed infection for the 3 years was 50% (95% CI, 26%–66%) for general practice patients and 39% (95% CI, 28%–47%) for patients admitted to hospital.

Conclusions: Influenza vaccines appeared to be similarly modestly effective in the general practice and hospital settings. Influenza vaccination appears to prevent hospital admission by preventing symptomatic infection rather than by attenuating the severity of illness.

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  • Heath A Kelly1
  • Courtney Lane2
  • Allen C Cheng3,4

  • 1 Victorian Infectious Diseases Reference Laboratory, Melbourne, VIC
  • 2 University of Melbourne, Melbourne, VIC
  • 3 Alfred Health, Melbourne, VIC
  • 4 Monash University, Melbourne, VIC

Correspondence: heath.kelly@mh.org.au

Acknowledgements: 

We gratefully acknowledge the contributions to the two surveillance schemes of the following people: Tom Kotsimbos, Paul Kelly, Deborah Friedman, Tony Korman and Louis Irving (FluCAN investigators); Kylie Carville and James Fielding (VicSPIN investigators) and Kristina Grant (VicSPIN data manager). We thank all hospital staff and general practices participating in the two surveillance schemes. FluCAN is funded by the Australian Department of Health. VicSPIN is supported by the Victorian Government Department of Health. Allen Cheng is supported by an NHMRC Career Development Fellowship.

Competing interests:

No relevant disclosures.

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access_time 10:41, 10 February 2016
Mark Jones

I have two comments/queries:
1. Was assessment of vaccination status performed blinded to case-control status?

2. Unfortunately this study design carries little clinical relevance, telling us very little about effectiveness in terms of preventing severe outcomes, absolute risk reduction and NNT. It really only tells us the odds of producing a negative PCR test with and without a record of vaccination. The discussion provides a hint of true efficacy where the authors discuss the need to carry out a randomised controlled trial with tens of thousands of participants to enable sufficient statistical power. This suggests the effect of vaccine is very small.

Competing Interests: No relevant disclosures

Dr Mark Jones
University of Queensland

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