Comparison 6. Case‐control studies.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Influenza vs influenza‐like illness (crude data)	9		Odds Ratio (M‐H, Random, 95% CI)	Subtotals only
1.1 Children aged below 6 years	9	4949	Odds Ratio (M‐H, Random, 95% CI)	0.59 [0.45, 0.77]
1.2 Children aged between 5 and 19 years	1	27	Odds Ratio (M‐H, Random, 95% CI)	0.76 [0.07, 8.66]
2 Influenza vs influenza‐like illness (adj. estimates)	9		Odds Ratio (Random, 95% CI)	Subtotals only
2.1 Children aged below 23 months ‐ fully vaccinated	7		Odds Ratio (Random, 95% CI)	0.60 [0.39, 0.94]
2.2 Children aged between 24 and 59 months ‐ fully vaccinated	4		Odds Ratio (Random, 95% CI)	0.40 [0.22, 0.70]
2.3 Children aged between 6 and 59 months ‐ fully vaccinated	5		Odds Ratio (Random, 95% CI)	0.45 [0.32, 0.62]
2.4 Children aged below 14 years old ‐ fully vaccinated	1		Odds Ratio (Random, 95% CI)	0.23 [0.06, 0.84]
3 Influenza‐like illness vs no symptoms	1	488	Odds Ratio (M‐H, Random, 95% CI)	0.49 [0.28, 0.86]
3.1 Inactivated vaccine (1 dose)	1	244	Odds Ratio (M‐H, Random, 95% CI)	0.53 [0.26, 1.07]
3.2 Inactivated vaccine (2 doses)	1	244	Odds Ratio (M‐H, Random, 95% CI)	0.44 [0.18, 1.10]