Summary of results in outcomes with pairwise meta-analysis
| Outcome | Comparison | Number of studies (number of participants) | OR/IRR (95% CI) (95% PI) | VE (95% CI) | tau2 (95% CI) | Q; Q df; Q P value | I2 | Certainty of evidence |
| Primary outcomes | ||||||||
| LCI | IIV3-HD : IIV3-SD | 3(41,753) | OR: 0.75 (0.63 to 0.88) (0.25,2.19) | . | 0.00 (0.00 to 2.72) | 1.00;2;0.61 | 0% | |
| IIV3-SD : Placebo | 2(330) | OR: 0.31 (0.13 to 0.75) | . | 0.33 | 1.40;1;0.25 | 26% | ||
| LC—matched strains (DiazGranados 2014 defined as Match) | IIV3-HD : IIV3-SD | 2(330) | OR: 0.74 (0.63 to 0.88) | . | 0.00 | 0.86;1;0.35 | 0% | |
| LCI—mismatched strains (DiazGranados 2014 defined as Match) | IIV3-HD : IIV3-SD | 1(9,158) | OR: 0.87 (0.56 to 1.36) | . | . | . | . | |
| LCI—matched strains (DiazGranados 2014 defined as Mismatch) | IIV3-HD : IIV3-SD | 1(612) | OR: 0.52 (0.35 to 0.77) | . | . | . | . | |
| LCI—mismatched strains (DiazGranados 2014 defined as Mismatch) | IIV3-HD : IIV3-SD | 2(31,141) | OR: 0.76 (0.64 to 0.90) | . | 0.00 | 0.11;1;0.75 | 0% | |
| ILI | IIV3-HD : IIV3-SD | 2(41141) | OR: 0.98 (0.93 to 1.02) | VE: 1.76 (−1.75 to 7.18) | 0.00 | 0.14;1;0.71 | 0% | High |
| IIV3-SD : Placebo | 2(854) | OR: 0.39 (0.15 to 1.02) | VE: 57.79 (−1.75 to 83.22) | 0.21 | 1.08;1;0.30 | 8% | Low | |
| Secondary outcomes | ||||||||
| ER Visit for ILI | IIV3-HD : IIV3-SD | 2(41,141) | OR: 0.94 (0.74 to 1.19) | . | 0.00 | 0.20;1;0.66 | 0% | Moderate |
| Hospitalisation for ILI | IIV3-HD : IIV3-SD | 2(41,141) | OR: 0.72 (0.57 to 0.92) | . | 0.00 | 0.40;1;0.52 | 0% | High |
| Hospitalisation for ARI | IIV3-HD : IIV3-SD | 2(84,991) | OR: 0.87 (0.79 to 0.95) | . | 0.00 | 0.00;1;0.98 | 0% | Moderate |
| Number of vascular events | IIV3-Adj : IIV3-SD | 2(7,577) | IRR: 0.83* (0.54 to 1.27) | . | 0.00 | 0.00;1;0.89 | 0% | |
| IIV3-HD : IIV3-SD | 4(45,656) | IRR: 0.74* (0.43 to 1.29) (0.21,2.58) | . | 0.23 (0.00 to 0.20) | 4.90;3;0.18 | 39% | ||
| Inpatient hospitalisation (any cause) | IIV3-HD : IIV3-SD | 3(38,816) | OR: 0.76 (0.40 to 1.42) (0.01,50.27) | . | 0.27 (0.01 to 3.22) | 14.00;2;0.00 | 86% | Low |
| Inpatient hospitalisation (any cause)—low RoB subgroup | IIV3-HD : IIV3-SD | 2(34,940) | OR: 0.76 (0.52 to 1.13) | . | 0.27 | 14.00;1;0.00 | 93% | Moderate |
| Inpatient hospitalisation (any cause)—over 80 years subgroup | IIV3-HD : IIV3-SD | 2(35,859) | OR: 0.92 (0.86 to 0.99) | . | 0.00 | 0.20;1;0.66 | 0% | Moderate |
| Outpatient visit | IIV3-HD : IIV3-SD | 2(41,141) | OR: 1.04 (0.99 to 1.09) | . | 0.00 | 0.80;1;0.38 | 0% | |
| IIV3-SD : Placebo | 2(814) | OR: 0.40 (0.07 to 2.14) | . | 1.09 | 4.30;1;0.04 | 77% | ||
| All-cause mortality | IIV3-Adj : IIV3-SD | 2(7,577) | OR: 1.09 (0.73 to 1.62) | . | 0.00 | 0.50;1;0.47 | 0% | |
| IIV3-HD : IIV3-SD | 6(101,187) | OR: 0.97 (0.92 to 1.02) (0.90,1.04) | . | 0.00 (0.00 to 0.02) | 1.20;5;0.95 | 0% | ||
| IIV4-SD : IIV3-SD | 3(3864) | OR: 1.08 (0.38 to 3.09) (0.00,970.40) | . | 0.00 (0.00 to 15.12) | 0.70;2;0.70 | 0% | ||
| IIV3-SD : Placebo | 2(854) | OR: 1.47 (0.43 to 5.06) | . | 0.00 | 0.20;1;0.66 | 0% | ||
| Influenza-related mortality | IIV3-Adj:IIV3-SD | 1(6,961) | OR: 0.75 (0.17 to 3.36) | . | ||||
| IIV4-SD:IIV3-SD | 1(1,741) | OR: 3.01 (0.12 to 73.19) | . | |||||
*Incidence rate ratios were reported for number of vascular events. Other outcomes included ORs.
Adj, adjuvanted; ARI, acute respiratory infection; HD, high dosage; IIV3, inactivated influenza vaccine trivalent; IIV4, IIV quadrivalent; ILI, influenza-like illness; IRR, incidence rate ratio; LCI, laboratory-confirmed influenza; PI, prediction interval; RR, relative risk; SD, standard dosage; VE, vaccine efficacy.