Comparison 1. Inactivated parenteral influenza vaccine versus placebo or 'do nothing'.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 Influenza	25	71221	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.36, 0.47]
1.1 WHO recommended ‐ matching vaccine	15	46444	Risk Ratio (M‐H, Random, 95% CI)	0.41 [0.34, 0.49]
1.2 WHO recommended ‐ vaccine matching absent or unknown	7	15068	Risk Ratio (M‐H, Random, 95% CI)	0.45 [0.34, 0.59]
1.3 Monovalent not WHO recommended ‐ vaccine matching	2	9675	Risk Ratio (M‐H, Random, 95% CI)	0.22 [0.10, 0.52]
1.4 Monovalent not WHO recommended ‐ vaccine matching ‐ high dose	1	34	Risk Ratio (M‐H, Random, 95% CI)	0.11 [0.00, 2.49]
2 Influenza‐like illness	16	25795	Risk Ratio (M‐H, Random, 95% CI)	0.84 [0.75, 0.95]
2.1 WHO recommended ‐ matching vaccine	7	4760	Risk Ratio (M‐H, Random, 95% CI)	0.84 [0.77, 0.91]
2.2 WHO recommended ‐ vaccine matching absent or unknown	7	20942	Risk Ratio (M‐H, Random, 95% CI)	0.90 [0.69, 1.18]
2.3 Monovalent not WHO recommended ‐ vaccine matching	1	59	Risk Ratio (M‐H, Random, 95% CI)	1.02 [0.28, 3.70]
2.4 Monovalent not WHO recommended ‐ vaccine matching ‐ high dose	1	34	Risk Ratio (M‐H, Random, 95% CI)	0.46 [0.09, 2.30]
3 Physician visits	2	2308	Risk Ratio (M‐H, Random, 95% CI)	0.87 [0.40, 1.89]
3.1 WHO recommended ‐ matching vaccine	1	1178	Risk Ratio (M‐H, Random, 95% CI)	0.58 [0.37, 0.91]
3.2 WHO recommended ‐ vaccine matching absent or unknown	1	1130	Risk Ratio (M‐H, Random, 95% CI)	1.28 [0.90, 1.83]
4 Days ill	3	3133	Mean Difference (IV, Random, 95% CI)	‐0.21 [‐0.98, 0.56]
4.1 WHO recommended ‐ matching vaccine	2	2003	Mean Difference (IV, Random, 95% CI)	‐0.58 [‐0.85, ‐0.32]
4.2 WHO recommended ‐ matching absent or unknown	1	1130	Mean Difference (IV, Random, 95% CI)	0.66 [0.16, 1.16]
5 Times any drugs were prescribed	2	2308	Mean Difference (IV, Random, 95% CI)	‐0.01 [‐0.03, 0.01]
5.1 WHO recommended ‐ matching vaccine	1	1178	Mean Difference (IV, Random, 95% CI)	‐0.02 [‐0.04, ‐0.00]
5.2 WHO recommended ‐ matching absent or unknown	1	1130	Mean Difference (IV, Random, 95% CI)	0.0 [‐0.00, 0.00]
6 Times antibiotic was prescribed	2	2308	Mean Difference (IV, Random, 95% CI)	‐0.02 [‐0.03, ‐0.01]
6.1 WHO recommended ‐ matching vaccine	1	1178	Mean Difference (IV, Random, 95% CI)	‐0.02 [‐0.03, ‐0.01]
6.2 WHO recommended ‐ matching absent or unknown	1	1130	Mean Difference (IV, Random, 95% CI)	‐0.01 [‐0.03, 0.01]
7 Working days lost	4	3726	Mean Difference (IV, Random, 95% CI)	‐0.04 [‐0.14, 0.06]
7.1 WHO recommended ‐ matching vaccine	3	2596	Mean Difference (IV, Random, 95% CI)	‐0.09 [‐0.19, 0.02]
7.2 WHO recommended ‐ matching absent or unknown	1	1130	Mean Difference (IV, Random, 95% CI)	0.09 [0.00, 0.18]
8 Hospitalisations	3	11924	Risk Ratio (M‐H, Random, 95% CI)	0.96 [0.85, 1.08]
8.1 WHO recommended ‐ matching vaccine	1	1178	Risk Ratio (M‐H, Random, 95% CI)	0.0 [0.0, 0.0]
8.2 WHO recommended ‐ vaccine matching absent or unknown	1	1130	Risk Ratio (M‐H, Random, 95% CI)	2.89 [0.12, 70.68]
8.3 Monovalent not WHO recommended ‐ vaccine matching	1	9616	Risk Ratio (M‐H, Random, 95% CI)	0.96 [0.85, 1.08]
9 Clinical cases (clinically defined without clear definition)	3	4259	Risk Ratio (M‐H, Random, 95% CI)	0.87 [0.72, 1.05]
9.1 WHO recommended ‐ matching vaccine	2	2056	Risk Ratio (M‐H, Random, 95% CI)	0.89 [0.64, 1.25]
9.2 WHO recommended ‐ vaccine matching absent or unknown	1	2203	Risk Ratio (M‐H, Random, 95% CI)	0.83 [0.69, 0.99]
10 Local harms	20		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
10.1 Local ‐ tenderness/soreness	20	35655	Risk Ratio (M‐H, Random, 95% CI)	3.13 [2.44, 4.02]
10.2 Local ‐ erythema	9	29499	Risk Ratio (M‐H, Random, 95% CI)	2.59 [1.77, 3.78]
10.3 Local ‐ induration	3	7786	Risk Ratio (M‐H, Random, 95% CI)	4.28 [1.25, 14.67]
10.4 Local ‐ arm stiffness	1	50	Risk Ratio (M‐H, Random, 95% CI)	1.62 [0.54, 4.83]
10.5 Local ‐ combined endpoint (any or highest symptom)	11	12307	Risk Ratio (M‐H, Random, 95% CI)	2.44 [1.82, 3.28]
11 Systemic harms	17		Risk Ratio (M‐H, Random, 95% CI)	Subtotals only
11.1 Systemic ‐ myalgia	11	35008	Risk Ratio (M‐H, Random, 95% CI)	1.74 [1.41, 2.14]
11.2 Systemic ‐ fever	13	23850	Risk Ratio (M‐H, Random, 95% CI)	1.55 [1.26, 1.91]
11.3 Systemic ‐ headache	14	35999	Risk Ratio (M‐H, Random, 95% CI)	1.14 [0.99, 1.30]
11.4 Systemic ‐ fatigue or indisposition	12	35788	Risk Ratio (M‐H, Random, 95% CI)	1.19 [1.05, 1.36]
11.5 Systemic ‐ nausea/vomiting	4	6315	Risk Ratio (M‐H, Random, 95% CI)	1.80 [0.65, 5.04]
11.6 Systemic ‐ malaise	3	26111	Risk Ratio (M‐H, Random, 95% CI)	1.51 [1.18, 1.92]
11.7 Systemic ‐ combined endpoint (any or highest symptom)	6	2128	Risk Ratio (M‐H, Random, 95% CI)	1.16 [0.87, 1.53]