Comparison 1. Influenza vaccines versus placebo: randomised controlled trials ‐ parenteral vaccine.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1.1 Influenza	3	2217	Risk Ratio (M‐H, Random, 95% CI)	0.42 [0.27, 0.66]
1.1.1 Outbreak ‐ vaccine matching ‐ community ‐ healthy and ill	1	1838	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.23, 0.74]
1.1.2 Outbreak ‐ vaccine matching ‐ psychiatric hospital	1	177	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.12, 1.06]
1.1.3 No outbreak ‐ vaccine matching ‐ nursing home ‐ healthy and ill	1	202	Risk Ratio (M‐H, Random, 95% CI)	0.50 [0.20, 1.25]
1.2 Influenza‐like illness	4	6894	Risk Ratio (M‐H, Random, 95% CI)	0.59 [0.47, 0.73]
1.2.1 Outbreak ‐ vaccine matching (circulating strains) ‐ community ‐ healthy	2	2047	Risk Ratio (M‐H, Random, 95% CI)	0.57 [0.42, 0.79]
1.2.2 Outbreak ‐ vaccine matching ‐ community ‐ risk groups	1	490	Risk Ratio (M‐H, Random, 95% CI)	0.87 [0.49, 1.53]
1.2.3 Outbreak ‐ vaccine matching ‐ nursing home ‐ healthy	1	4180	Risk Ratio (M‐H, Random, 95% CI)	0.54 [0.37, 0.80]
1.2.4 Outbreak ‐ vaccine matching ‐ psychiatric hospital	1	177	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.13, 0.92]
1.3 Pneumonia	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
1.3.1 Outbreak ‐ vaccine matching ‐ community ‐ healthy	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
1.4 All deaths	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
1.4.1 Outbreak ‐ vaccine matching ‐ community ‐ healthy	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected