Table 3.
The effectiveness of booster immunization of the COVID-19 vaccine to prevent SARS-CoV-2 infection and COVID-19 caused by the Delta variant*.
| Type of disease | Variant | No. of studies | RR/OR (95% CI) | P h/I 2 (%)& | VE (%) (95% CI)# | P | Vaccine name |
|---|---|---|---|---|---|---|---|
| Comparison between one dose booster vaccinees and unvaccinated group | |||||||
| Cohort studies | |||||||
| SARS-CoV-2 infection | Overall | 9 | 0.141 (0.084, 0.238) | <0.001/98.9 | 85.9 (76.2, 91.6) | <0.001 | |
| RNA-based vaccine | 6 | 0.145 (0.067, 0.313) | <0.001/99.3 | 85.5 (68.7, 93.3) | <0.001 | BNT16b2; mRNA-1273 | |
| Symptomatic COVID-19 | Overall | 5 | 0.252 (0.162, 0.392) | <0.001/97.4 | 74.8 (60.8, 83.8) | <0.001 | |
| RNA-based vaccine | 4 | 0.211 (0.144, 0.307) | <0.001/95.2 | 78.9 (69.3, 85.6) | <0.001 | BNT16b2; mRNA-1273 | |
| Severe COVID-19 | Overall | 5 | 0.056 (0.043, 0.071) | <0.001/92.9 | 94.4 (92.9, 95.7) | <0.001 | |
| RNA-based vaccine | 4 | 0.061 (0.046, 0.083) | <0.001/88.9 | 93.9 (91.7, 95.4) | <0.001 | BNT16b2; mRNA-1273 | |
| COVID-19-related death | Overall | 2 | 0.040 (0.036, 0.045) | 1.000/0.0 | 96.0 (95.5, 96.7) | <0.001 | |
| RNA-based vaccine | 1 | 0.040 (0.020, 0.070) | NA | 96.0 (93.0, 98.0) | <0.001 | BNT16b2; mRNA-1273 | |
| Case–control studies | |||||||
| SARS-CoV-2 infection | Overall | 5 | 0.062 (0.036, 0.105) | <0.001/85.8 | 93.8 (89.5, 96.4) | <0.001 | |
| RNA-based vaccine | 4 | 0.052 (0.027, 0.093) | <0.001/87.9 | 94.8 (90.7, 97.3) | <0.001 | BNT16b2; mRNA-1273 | |
| Symptomatic COVID-19 | Overall | 8 | 0.052 (0.042, 0.064) | <0.001/89.8 | 94.8 (93.6, 95.8) | <0.001 | BNT16b2; mRNA-1273 |
| Severe COVID-19 | Overall | 6 | 0.021 (0.009, 0.043) | <0.001/96.4 | 97.9 (95.7, 99.1) | <0.001 | BNT16b2; mRNA-1273 |
| COVID-19-related death | Overall | 1 | 0.040 (0.010, 0.120) | NA | 96.0 (88.0, 99.0) | <0.001 | BNT16b2; mRNA-1273 |
| Comparison between one-dose booster vaccinees and non-booster vaccinees groups | |||||||
| Cohort studies | |||||||
| SARS-CoV-2 infection | Overall | 10 | 0.179 (0.124, 0.259) | <0.001/96.4 | 82.1 (74.1, 87.6) | <0.001 | BNT162b2; mRNA-1273 |
| Symptomatic COVID-19 | Overall | 2 | 0.092 (0.077, 0.105) | 0.699/0.0 | 90.8 (89.5, 92.3) | <0.001 | BNT162b2 |
| Severe COVID-19 | Overall | 3 | 0.074 (0.038, 0.142) | 0.097/57.2 | 92.6 (85.8, 96.2) | <0.001 | BNT162b2, mRNA-1273 |
| Case–control studies | |||||||
| Symptomatic COVID-19 | Overall | 3 | 0.155 (0.136, 0.176) | 0.012/77.3 | 84.5 (82.4, 86.4) | <0.001 | BNT162b2; mRNA-1273 |
*Comparison between booster vaccinees and unvaccinated group; #Vaccine effectiveness = 100*(1–RR) % or 100* (1-OR) %; &NA, not available.