Comparison 1. Inactivated influenza vaccine versus placebo.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Total exacerbations per participant	2	180	Mean Difference (IV, Fixed, 95% CI)	‐0.37 [‐0.64, ‐0.11]
2 Early exacerbations per participant	2	180	Mean Difference (IV, Fixed, 95% CI)	0.01 [‐0.11, 0.13]
3 Late exacerbations per participant	2	180	Mean Difference (IV, Fixed, 95% CI)	‐0.39 [‐0.61, ‐0.18]
4 Participants with at least one exacerbation or acute respiratory illness	3	222	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.81 [0.44, 1.48]
4.1 Clinical exacerbations	2	97	Peto Odds Ratio (Peto, Fixed, 95% CI)	1.06 [0.48, 2.33]
4.2 Any acute respiratory illness	1	125	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.56 [0.22, 1.42]
5 Participants with early exacerbations	2	180	Peto Odds Ratio (Peto, Fixed, 95% CI)	1.08 [0.52, 2.26]
6 Participants with late exacerbations	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected
7 Hospital admissions	2	180	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.33 [0.09, 1.24]
7.1 Clinical exacerbations	1	55	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.14 [0.01, 2.39]
7.2 Influenza‐related exacerbations	1	125	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.41 [0.09, 1.89]
8 Mortality (all cause)	2	180	Peto Odds Ratio (Peto, Fixed, 95% CI)	0.87 [0.28, 2.70]
9 Mortality (acute respiratory illness‐related)	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
10 Overall change in lung function (FEV¹, L)	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
11 Change in early lung function (FEV¹, L)	1		Mean Difference (IV, Fixed, 95% CI)	Totals not selected
12 Systemic adverse effects	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
13 Local effects at injection site	1		Odds Ratio (M‐H, Fixed, 95% CI)	Totals not selected
14 Participants with early breathlessness	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected
15 Participants with early tightness	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected
16 Participants with early wheeze	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected
17 Participants with early cough	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected
18 Acute respiratory illness subsequently documented as influenza‐related	2	180	Odds Ratio (M‐H, Fixed, 95% CI)	0.19 [0.07, 0.48]
18.1 FEV¹ ≥ 70% predicted	1	45	Odds Ratio (M‐H, Fixed, 95% CI)	0.12 [0.01, 1.11]
18.2 Participants with chronic bronchitis	1	55	Odds Ratio (M‐H, Fixed, 95% CI)	0.19 [0.04, 0.96]
18.3 FEV¹ < 50% predicted	1	47	Odds Ratio (M‐H, Fixed, 95% CI)	0.11 [0.01, 0.99]
18.4 FEV¹ 50% to 69% predicted	1	33	Odds Ratio (M‐H, Fixed, 95% CI)	0.46 [0.07, 2.98]
19 Early acute respiratory illness (ARI)	1	250	Odds Ratio (M‐H, Fixed, 95% CI)	0.72 [0.34, 1.50]
19.1 ARI within 1 week of vaccination	1	125	Odds Ratio (M‐H, Fixed, 95% CI)	1.02 [0.24, 4.26]
19.2 ARI between 1 and 4 weeks after vaccination	1	125	Odds Ratio (M‐H, Fixed, 95% CI)	0.63 [0.27, 1.50]
20 Participants with early sputum production	1		Peto Odds Ratio (Peto, Fixed, 95% CI)	Totals not selected