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Review
. 2016 Oct 20;21(42):30378.
doi: 10.2807/1560-7917.ES.2016.21.42.30378.

Herd effect from influenza vaccination in non-healthcare settings: a systematic review of randomised controlled trials and observational studies

Dominik Mertz  1 , Shaza A Fadel, Po-Po Lam, Dat Tran, Jocelyn A Srigley, Sandra A Asner, Michelle Science, Stefan P Kuster, Johannes Nemeth, Jennie Johnstone, Justin R Ortiz, Mark Loeb
Affiliations
Review

Herd effect from influenza vaccination in non-healthcare settings: a systematic review of randomised controlled trials and observational studies

Dominik Mertz et al. Euro Surveill. .

Abstract

Influenza vaccination programmes are assumed to have a herd effect and protect contacts of vaccinated persons from influenza virus infection. We searched MEDLINE, EMBASE, the Cumulative Index to Nursing and Allied Health Literature (CINAHL), Global Health and the Cochrane Central Register of Controlled Trials (CENTRAL) from inception to March 2014 for studies assessing the protective effect of influenza vaccination vs no vaccination on influenza virus infections in contacts. We calculated odds ratios (ORs) and 95% confidence intervals (CIs) using a random-effects model. Of 43,082 screened articles, nine randomised controlled trials (RCTs) and four observational studies were eligible. Among the RCTs, no statistically significant herd effect on the occurrence of influenza in contacts could be found (OR: 0.62; 95% CI: 0.34-1.12). The one RCT conducted in a community setting, however, showed a significant effect (OR: 0.39; 95% CI: 0.26-0.57), as did the observational studies (OR: 0.57; 95% CI: 0.43-0.77). We found only a few studies that quantified the herd effect of vaccination, all studies except one were conducted in children, and the overall evidence was graded as low. The evidence is too limited to conclude in what setting(s) a herd effect may or may not be achieved.

Keywords: herd effect; indirect effect; influenza; systematic review; vaccine-preventable diseases; vaccines and immunisation.

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Conflict of interest statement

SPK received travel grants from Pfizer and Novartis. DT received grant funding from GSK Canada. SAF, PL, JS, SAA, MS, JN, JJ, JRO, DM, ML: none declared.

Figures

Figure 1
Figure 1
Flowchart of included and excluded randomised control trials and observational studies identified in a systematic review of herd effect from influenza vaccination in non-healthcare settings
Figure 2
Figure 2
Meta-analysis of seven included randomised controlled trials reporting on influenza infections in contacts of influenza vaccinated vs unvaccinated individuals in non-healthcare settings
Figure 3
Figure 3
Meta-analysis of four included observational studies reporting on influenza infections in contacts of influenza vaccinated vs unvaccinated patients in non-healthcare settings
See this image and copyright information in PMC

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