Table 1 Effectiveness of a single dose and two doses of SARS-CoV-2 vaccines
| Â | No. cohorts | Vaccine effectiveness (%) (95% CI) | I2 (%) | P value for heterogeneity | P value for subgroup differences | Weight (%) |
|---|---|---|---|---|---|---|
The first dose | ||||||
Prevention of SARS-CoV-2 infection | ||||||
Overall | 44 | 41 (28–54) | 99.6 |  < 0.001 |  < 0.001 | 100 |
 < 7 days after the first dose | 3 | 1 (− 25–27) | 84.0 | 0.002 |  | 6.92 |
 < 14 days after the first dose | 4 | 12 (0–24) | 0.0 | 0.759 |  | 6.78 |
 ≥ 7 days after the first dose | 5 | 17 (− 20–55) | 95.3 |  < 0.001 |  | 10.61 |
 ≥ 14 days after the first dose | 20 | 48 (31–66) | 99.4 |  < 0.001 |  | 46.63 |
 ≥ 21 days after the first dose | 8 | 56 (42–70) | 92.6 |  < 0.001 |  | 19.45 |
1 dose | 3 | 32 (9–54) | 83.4 | 0.002 |  | 7.11 |
 ≥ 1 dose | 1 | 95 (94–96) | .. | .. |  | 2.50 |
Prevention of symptomatic COVID-19 | ||||||
Overall | 14 | 52 (31–73) | 99.2 |  < 0.001 |  < 0.001 | 100 |
 < 7 days after the first dose | 1 | 19 (0–45) | .. | .. |  | 6.79 |
 ≥ 7 days after the first dose | 2 | 45 (− 43–100) | 99.8 |  < 0.001 |  | 14.63 |
 ≥ 14 days after the first dose | 5 | 53 (43–62) | 64.2 | 0.025 |  | 35.24 |
 ≥ 21 days after the first dose | 2 | 63 (7–100) | 99.1 |  < 0.001 |  | 14.56 |
1 dose | 3 | 44 (14–74) | 94.4 |  < 0.001 |  | 21.43 |
 ≥ 1 dose | 1 | 95 (92–97) | .. | .. |  | 7.34 |
Prevention of COVID-19 hospital admissions | ||||||
Overall | 8 | 66 (50–81) | 98.5 |  < 0.001 | 0.005 | 100 |
 < 7 days after the first dose | 1 | 74 (71–77) | .. | .. |  | 13.47 |
 ≥ 7 days after the first dose | 1 | 61 (47–75) | .. | .. |  | 12.27 |
 ≥ 14 days after the first dose | 5 | 61 (41–81) | 97.9 |  < 0.001 |  | 60.93 |
 ≥ 21 days after the first dose | 1 | 82 (77–88) | .. | .. |  | 13.33 |
Prevention of COVID-19 ICU admissions | ||||||
Overall | 3 | 45 (42–49) | 39.5 | 0.192 | .. | 100 |
 ≥ 14 days after the first dose | 3 | 45 (42–49) | 39.5 | 0.192 |  | 100 |
Prevention of COVID-19-related death | ||||||
Overall | 4 | 53 (15–91) | 98.9 |  < 0.001 |  < 0.001 | 100 |
 ≥ 14 days after the first dose | 3 | 44 (23–64) | 58.1 | 0.092 |  | 70.60 |
 ≥ 1 dose | 1 | 97 (91–99) | .. | .. |  | 29.40 |
The second dose | ||||||
Prevention of SARS-CoV-2 infection | ||||||
Overall | 34 | 85 (81–89) | 99.5 |  < 0.001 |  < 0.001 | 100 |
 < 7 days after the second dose | 3 | 75 (51–99) | 95.7 |  < 0.001 |  | 8.72 |
 < 14 days after the second dose | 2 | 70 (49–91) | 70.8 | 0.064 |  | 4.77 |
 ≥ 7 days after the second dose | 14 | 91 (88–93) | 76.5 |  < 0.001 |  | 42.72 |
 ≥ 14 days after the second dose | 13 | 81 (71–92) | 99.8 |  < 0.001 |  | 37.35 |
 ≥ 21 days after the second dose | 1 | 94 (78–98) | .. | .. |  | 2.91 |
2 doses | 1 | 98 (96–99) | .. | .. |  | 3.52 |
Prevention of symptomatic COVID-19 | ||||||
Overall | 17 | 97 (97–98) | 83.6 |  < 0.001 | 0.008 | 100 |
 < 7 days after the second dose | 1 | 100 (94–100) | .. | .. |  | 5.53 |
 < 14 days after the second dose | 2 | 75 (59–92) | 46.5 | 0.171 |  | 0.47 |
 ≥ 7 days after the second dose | 5 | 97 (96–98) | 17.4 | 0.304 |  | 32.25 |
 ≥ 14 days after the second dose | 7 | 96 (94–98) | 87.9 |  < 0.001 |  | 46.53 |
 ≥ 21 days after the second dose | 1 | 99 (94–100) | .. | .. |  | 5.67 |
2 doses | 1 | 99 (96–100) | .. | .. |  | 9.54 |
Prevention of COVID-19 hospital admissions | ||||||
Overall | 8 | 93 (89–96) | 99.0 |  < 0.001 | 0.991 | 100 |
 ≥ 7 days after the second dose | 3 | 93 (84–100) | 72.5 | 0.026 |  | 35.70 |
 ≥ 14 days after the second dose | 5 | 93 (85–100) | 99.4 |  < 0.001 |  | 64.3 |
Prevention of COVID-19 ICU admissions | ||||||
Overall | 8 | 96 (93–98) | 96.4 |  < 0.001 | 0.414 | 100 |
 ≥ 7 days after the second dose | 4 | 97 (93–100) | 18.2 | 0.300 |  | 38.11 |
 ≥ 14 days after the second dose | 4 | 94 (87–100) | 98.4 |  < 0.001 |  | 61.89 |
Prevention of COVID-19-related death | ||||||
Overall | 8 | 95 (92–98) | 96.3 |  < 0.001 | 0.851 | 100 |
 < 14 days after the second dose | 1 | 96 (83–99) | .. | .. |  | 8.68 |
 ≥ 7 days after the second dose | 3 | 97 (95–98) | 11.7 | 0.322 |  | 37.91 |
 ≥ 14 days after the second dose | 3 | 93 (82–100) | 98.9 |  < 0.001 |  | 42.36 |
2 doses | 1 | 98 (87–100) | .. | .. |  | 11.06 |