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Clin Infect Dis. 2017 Sep 1;65(5):719-728. doi: 10.1093/cid/cix420.

Systematic Review and Meta-analysis of Indirect Protection Afforded by Vaccinating Children Against Seasonal Influenza: Implications for Policy.

Yin JK1,2,3, Heywood AE4, Georgousakis M1,2,3, King C1,2,5, Chiu C1,2,5, Isaacs D2,5, Macartney KK1,2,5.

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National Centre for Immunisation Research and Surveillance, Westmead.
The Children's Hospital at Westmead.
Sydney School of Public Health, Faculty of Medicine, University of Sydney.
School of Public Health and Community Medicine, University of New South Wales.
Discipline of Child and Adolescent Health, Faculty of Medicine, University of Sydney, New South Wales, Australia.



Universal childhood vaccination is a potential solution to reduce seasonal influenza burden.


We reviewed systematically the literature on "herd"/indirect protection from vaccinating children aged 6 months to 17 years against influenza.


Of 30 studies included, 14 (including 1 cluster randomized controlled trial [cRCT]) used live attenuated influenza vaccine, 11 (7 cRCTs) used inactivated influenza vaccine, and 5 (1 cRCT) compared both vaccine types. Twenty of 30 studies reported statistically significant indirect protection effectiveness (IPE) with point estimates ranging from 4% to 66%. Meta-regression suggests that studies with high quality and/or sufficiently large sample size are more likely to report significant IPE. In meta-analyses of 6 cRCTs with full randomization (rated as moderate quality overall), significant IPE was found in 1 cRCT in closely connected communities where school-aged children were vaccinated: 60% (95% confidence interval [CI], 41%-72%; I2 = 0%; N = 2326) against laboratory-confirmed influenza, and 3 household cRCTs in which preschool-aged children were vaccinated: 22% (95% CI, 1%-38%; I2 = 0%; N = 1903) against acute respiratory infections or influenza-like illness. Significant IPE was also reported in a large-scale cRCT (N = 8510) that was not fully randomized, and 3 ecological studies (N > 10000) of moderate quality including 36% reduction in influenza-related mortality among the elderly in a Japanese school-based program. Data on IPE in other settings are heterogeneous and lacked power to draw a firm conclusion.


The available evidence suggests that influenza vaccination of children confers indirect protection in some but not all settings. Robust, large-scaled studies are required to better quantify the indirect protection from vaccinating children for different settings/endpoints.


children; immunization policy; indirect protection; influenza vaccine; seasonal influenza

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