1916. Herd Effect from Influenza Vaccination in Non-Healthcare Settings: a Systematic Review of Randomised Controlled and Observational Studies
Session: Poster Abstract Session: Vaccines: Influenza
Saturday, October 10, 2015
Room: Poster Hall
  • SR Herd immunity ID Week.pdf (158.6 kB)
  • Background: Influenza vaccine programs are expected to have a herd effect and protect close contacts of vaccinated persons from influenza virus infection. 

    Methods: We searched MEDLINE, EMBASE, CINAHL, Global Health and CENTRAL from inception to March 2014 for studies assessing the protective effect of influenza vaccination versus no vaccination on influenza virus infections in contacts. We excluded studies conducted in a health care setting, and ecological and modelling studies. We evaluated risk of bias and applied GRADE to assess the level of evidence. We calculated odds ratio (OR) and 95% confidence intervals (CI) using a random-effects model.

    Results: Out of 43,082 screened articles, nine randomized controlled trials (RCTs) and four observational studies were eligible. Most studies were conducted in North America (n=7). Among RCTs, no significant herd effect on the occurrence of influenza in contacts could be found (OR 0.62, 95% CI 0.34-1.12). However, two additional RCTs that could not be included in meta-analysis supported a herd effect, as did observational studies (OR 0.57, 95% CI 0.43-0.77). Data on hospital admission, pneumonia, and death were scarce, and no conclusions could be made. Applying GRADE, the evidence supporting a herd effect to prevent influenza was assessed to be low.

    Conclusion: Herd effects are expected with influenza vaccine programs, but there are only few studies that quantify the indirect effects of vaccination and the overall evidence was graded as low, with better evidence in studies conducted in a community setting. Further high-quality studies are needed.

    Dominik Mertz, MD, MSc1, Shaza Fadel, MSc2, Po-Po Lam, MSc3, Dat Tran, MD, MSc4, Jocelyn Srigley, MD, MSc5, Sandra Asner, MD, MSc6, Michelle Science, MD, FRCPC7, Stefan Kuster, MD, MSc8, Johannes Nemeth, MD8, Jennie Johnstone, MD, PhD, FRCPC9, Justin Ortiz, MD10 and Mark Loeb, MD, MSc, FSHEA1, (1)McMaster University, Hamilton, ON, Canada, (2)Centre for Global Health Research, Toronto, ON, Canada, (3)University of Toronto, Toronto, ON, Canada, (4)Division of Infectious Diseases, Department of Pediatrics, Hospital for Sick Children, The University of Toronto, Toronto, ON, Canada, (5)BC Children’s & Women's Hospitals, Vancouver, BC, Canada, (6)University Hospital Lausanne, Lausanne, Switzerland, (7)Pediatrics, The Hospital for Sick Children, Toronto, ON, Canada, (8)University Hospital Zurich, Zurich, Switzerland, (9)Infection Prevention and Control, Public Health Ontario, Toronto, ON, Canada, (10)World Health Organization, Geneva, Switzerland


    D. Mertz, None

    S. Fadel, None

    P. P. Lam, None

    D. Tran, None

    J. Srigley, None

    S. Asner, None

    M. Science, None

    S. Kuster, None

    J. Nemeth, None

    J. Johnstone, None

    J. Ortiz, None

    M. Loeb, None

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