title: Herd effect from influenza vaccination in non-healthcare settings: a systematic review of randomised controlled trials and observational studies.
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.
authors: Department of Medicine, McMaster University, Hamilton, Canada.
authors: Dominik
authors: D
authors: Mertz
authors: Shaza A
authors: SA
authors: Fadel
authors: Po-Po
authors: PP
authors: Lam
authors: Dat
authors: D
authors: Tran
authors: Jocelyn A
authors: JA
authors: Srigley
authors: Sandra A
authors: SA
authors: Asner
authors: Michelle
authors: M
authors: Science
authors: Stefan P
authors: SP
authors: Kuster
authors: Johannes
authors: J
authors: Nemeth
authors: Jennie
authors: J
authors: Johnstone
authors: Justin R
authors: JR
authors: Ortiz
authors: Mark
authors: M
authors: Loeb
mesh_terms: D006801:Humans; D007252:Influenza Vaccines / Q000008:administration & dosage*; D007251:Influenza, Human / Q000517:prevention & control*; D064887:Observational Studies as Topic; D016032:Randomized Controlled Trials as Topic; D014611:Vaccination
chemical_list: D007252:Influenza Vaccines
keywords: herd effect; indirect effect; influenza; systematic review; vaccine-preventable diseases; vaccines and immunisation