Summary of findings 4. ChAdOx1 – AstraZeneca + University of Oxford compared to placebo for vaccination against COVID‐19a.
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants (studies) | Certainty of the evidence | Comments | |
| Risk with placebo | Risk with ChAdOx1 | |||||
| Confirmed SARS‐CoV‐2 infectionb | 3199 per 100,000 | 1300 per 100,000 (1017 to 1663) |
VE 59.35 (48.00 to 68.22) |
43,390 (5 RCTs)c | ⊕⊕⊕⊖ Moderated,e | Substantial heterogeneity (I² = 68%) between included studies: Falsey 2021 (VE 64.35%, 95% CI 56.10% to 71.00%; n = 26,212); Voysey 2021a (VE 54.10%, 95% CI 44.70% to 61.90%; n = 17,178) |
| Confirmed symptomatic COVID‐19b | 2207 per 100,000 | 657 per 100,000 (516 to 836) |
VE 70.23 (62.10 to 76.62) |
43,390 (5 RCTs)c | ⊕⊕⊕⊕ Highd | — |
| Severe or critical COVID‐19 | Outcome not yet measured or reported | |||||
| All‐cause mortalityf | 52 per 100,000 | 25 per 100,000 (10 to 59) | RR 0.48 (0.20 to 1.14) | 56,727 (5 RCTs)g | ⊕⊕⊖⊖ Lowh | 2 additional trials (Asano 2022; Kulkarni 2021) reported this outcome in 1392 participants (192 ChAdOx1 versus 64 placebo and 900 SII‐ChAdOx1 versus 300 placebo, respectively). There were no events in either group in either trial and they did not contribute to the pooled effect estimate. |
| Systemic reactogenicity eventsi | 141 per 1000 | 553 per 1000 (297 to 1000) | RR 3.93 (2.11 to 7.29) | 256 (1 RCT)j | ⊕⊕⊕⊖ Moderatek | — |
| Any adverse eventl | Outcome not pooled due to considerable heterogeneity (I² = 90%) between included studies: Asano 2022 (RR 2.54, 95% CI 1.73 to 3.74; n = 256); Falsey 2021 (RR 1.37, 95% CI 1.33 to 1.42; n = 32,379); Kulkarni 2021 (RR 1.39, 95% CI 1.12 to 1.74; n = 1200); Voysey 2021a (RR 0.74, 95% CI 0.56 to 0.96; n = 23,745) | — | 57,580 (7 RCTs)m | ⊕⊕⊖⊖ Lown | — | |
| Serious adverse eventso | 794 per 100,000 | 699 per 100,000 (572 to 850) | RR 0.88 (0.72 to 1.07) | 58,182 (7 RCTs)p | ⊕⊕⊕⊖ Moderateq | — |
| Local reactogenicity eventsi | 94 per 1000 | 604 per 1000 (279 to 1000) | RR 6.44 (2.98 to 13.92) | 256 (1 RCT)j | ⊕⊕⊕⊖ Moderatek,r | — |
| *The risk in the intervention group (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). COVID‐19: coronavirus disease 2019 CI: confidence interval; RCT: randomized controlled trial; RR: risk ratio; SARS‐CoV‐2: severe acute respiratory syndrome coronavirus 2; VE: vaccine efficacy. | ||||||
| GRADE Working Group grades of evidence High certainty: we are very confident that the true effect lies close to that of the estimate of the effect. Moderate certainty: we are moderately confident in the effect estimate; the true effect is likely to be close to the estimate of the effect, but there is a possibility that it is substantially different. Low certainty: our confidence in the effect estimate is limited; the true effect may be substantially different from the estimate of the effect. Very low certainty: we have very little confidence in the effect estimate; the true effect is likely to be substantially different from the estimate of effect. | ||||||
aLast updated: 4 May 2022 bFollow‐up: from 14 days after second dose up to 1.34 months (median) and 2 months (median) cFalsey 2021; Voysey 2021a (data from four pooled RCTs) dDespite some concerns with deviations from intervention, not downgraded for risk of bias. eInconsistency: downgraded one level (I² = 68%). fFollow‐up: 2 months, 4.2 months and 2 months (median) gFalsey 2021; Voysey 2021a (data from four pooled RCTs); Madhi 2021a (participants with HIV, trial already counted in Voysey 2021a) hImprecision: downgraded two levels due to small number of events observed and wide CIs that encompass a potential benefit and a potential harm with the intervention. iFollow‐up: seven days jAsano 2022 kImprecision: downgraded one level due to low number of participants/few events observed. lFollow‐up: 1 month, 1.16 months, 1.9 months, and 3.4 months mAsano 2022; Falsey 2021; Kulkarni 2021; Voysey 2021a (data from four pooled RCTs) nInconsistency: downgraded two levels (I² = 90%). oFollow‐up: 1 month, 1.9 months, 6 months, and 3.64 months (median) pAsano 2022; Falsey 2021; Kulkarni 2021; Voysey 2021a (data from four pooled RCTs). Madhi 2021a (participants with HIV, trial already counted in Voysey 2021a) qImprecision: downgraded one level due to wide CIs consistent with the possibility of benefit and the possibility of no effect. rDespite some concerns with selection of reported results, not downgraded for risk of bias.