Comparison 2.

Inactivated vaccine versus placebo or no intervention (RCTs by age group)

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Influenza	5	1628	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.29, 0.59]
1.1 under 2 years	2	786	Risk Ratio (M‐H, Random, 95% CI)	0.55 [0.18, 1.69]
1.2 under 6 years	2	132	Risk Ratio (M‐H, Random, 95% CI)	0.61 [0.34, 1.08]
1.3 over 6 years	3	710	Risk Ratio (M‐H, Random, 95% CI)	0.31 [0.22, 0.45]
2 Influenza‐like illness	5	19388	Risk Ratio (M‐H, Random, 95% CI)	0.64 [0.54, 0.76]
2.1 under 2 years	0	0	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
2.2 under 6 years	3	476	Risk Ratio (M‐H, Random, 95% CI)	0.39 [0.21, 0.69]
2.3 over 6 years	4	18912	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.66, 0.78]