Comparison 2. Inactivated vaccine versus placebo (RCTs).

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)	0.36 [0.28, 0.48]
2 Influenza‐like illness	4	19044	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.65, 0.79]
2.1 Inactivated vaccines (1 dose)	2	267	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.15, 0.81]
2.2 Inactivated vaccines (2 doses)	2	18777	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.69, 0.76]
3 Acute otitis media	3	884	Risk Ratio (M‐H, Random, 95% CI)	1.15 [0.95, 1.40]
3.1 Inactivated vaccines (1 dose)	1	136	Risk Ratio (M‐H, Random, 95% CI)	1.52 [0.10, 23.76]
3.2 Inactivated vaccines (2 doses)	2	748	Risk Ratio (M‐H, Random, 95% CI)	1.15 [0.95, 1.40]
4 School absenteeism	1		Risk Ratio (M‐H, Random, 95% CI)	Totals not selected
5 Influenza‐like illness (clustering sensitivity analysis)	4	6126	Risk Ratio (M‐H, Random, 95% CI)	0.70 [0.60, 0.82]
5.1 Inactivated vaccines (1 dose)	2	267	Risk Ratio (M‐H, Random, 95% CI)	0.35 [0.15, 0.81]
5.2 Inactivated vaccines (2 doses)	2	5859	Risk Ratio (M‐H, Random, 95% CI)	0.72 [0.66, 0.79]