Table 7 Meta-regression analysis of factors associated with VE against severe COVID-19

Study region^a

 Western Pacific region

Ref

–

–

–

1

–

 Region of Americas

0.463

(0.035, 0.891)

0.034

0.214

1.589

(1.036, 2.438)

 European region

2.587

(1.757, 3.418)

 < 0.001

0.416

13.290

(5.795, 30.508)

 Region of South-East Asia

0.077

(− 0.663, 0.816)

0.837

0.370

1.080

(0.515, 2.261)

 Eastern Mediterranean region

 − 0.001

(− 0.505, 0.502)

0.996

0.252

0.999

(0.604, 1.652)

VOC

 Alpha

Ref

–

–

–

1

–

 Gamma

0.786

(0.063, 1.510)

0.034

0.362

2.195

(1.065, 4.527)

 Delta

0.983

(0.413, 1.553)

0.001

0.286

2.672

(1.511, 4.726)

 Omicron

1.138

(0.479, 1.798)

0.001

0.330

3.121

(1.614, 6.038)

 Others

0.415

(− 0.283, 1.112)

0.240

0.350

1.514

(0.754, 3.040)

Population type

 General

Ref

–

–

–

1

–

 HCWs

0.757

(− 0.717, 2.230)

0.309

0.738

2.132

(0.488, 9.300)

 COVID-19 inpatient

1.346

(0.738, 1.955)

 < 0.001

0.305

3.842

(2.092, 7.064)

 Chronical patient

0.512

(− 0.147, 1.171)

0.126

0.330

1.669

(0.863, 3.225)

Age range

 18–59

Ref

–

–

–

1

–

  < 18

 − 0.546

(− 1.184, 0.093)

0.093

0.320

0.579

(0.306, 1.097)

  ≥ 60

0.568

(0.290, 0.847)

 < 0.001

0.140

1.765

(1.336, 2.333)

 Others^b

0.503

(− 0.180, 1.186)

0.146

0.342

1.654

(0.835, 3.274)

Vaccine doses

 Primary

Ref

–

–

–

1

–

 Booster

 − 0.614

(− 0.972, − 0.257)

0.001

0.179

0.541

(0.378, 0.773)

Study design

 Cohort study^c

Ref

–

–

–

1

–

 Retrospective cohort study

0.883

(0.447, 1.319)

 < 0.001

0.218

2.418

(1.564, 3.740)

 Case–control study

0.103

(− 0.290, 0.496)

0.603

0.197

1.108

(0.748, 1.642)

 Descriptive study

 − 1.863

(− 2.685, − 1.040)

 < 0.001

0.412

0.155

(0.068, 0.353)

 Constant

 − 2.789

(− 3.549, − 2.029)

 < 0.001

0.381

0.061

(0.029, 0.131)