Summary of findings 15. Booster compared to placebo/no booster for vaccination against COVID‐19a.
| Outcomes | Anticipated absolute effects* (95% CI) | Relative effect (95% CI) | № of participants | Certainty of the evidence | Comments | |
| Risk with placebo/no booster | Risk with booster | |||||
| Confirmed SARS‐CoV‐2 infection | Outcome not yet measured or reported | |||||
| Confirmed symptomatic COVID‐19 | Outcome not yet measured or reported | |||||
| Severe or critical COVID‐19 | Outcome not yet measured or reported | |||||
| All‐cause mortalityb | 63 per 100,000 | 80 per 100,000 (33 to 191) | RR 1.27 (0.52 to 3.05) | 28,254 (1 RCT)c | ⊕⊖⊖⊖ Very lowd,e | — |
| Systemic reactogenicity eventsf | 102 per 1000 | 183 per 1000 (72 to 464) | RR 1.80 (0.71 to 4.56) | 119 (1 RCT)g | ⊕⊕⊖⊖ Lowd | — |
| Any adverse event | Outcome not yet measured or reported | |||||
| Serious adverse events | Outcome not yet measured or reported | |||||
| Local reactogenicity eventsf | 119 per 1000 | 766 per 1000 (377 to 1000) | RR 6.46 (3.18 to 13.13) | 119 (1 RCT)g | ⊕⊕⊕⊖ Moderateh | — |
| *The risk in the intervention group (and its 95% CI) 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. | ||||||
| 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: 1.7 months (median) cToledo‐Romani 2021: FINLAY‐FR‐2/booster FR‐1 versus FINLAY‐FR‐2 dImprecision: downgraded two levels due to wide CIs consistent with the possibility of benefit and the possibility of harm and few events. eRisk of bias downgraded one level: some concerns regarding adequate randomization and deviation from intended intervention. fFollow‐up: seven days gHall 2021: mRNA‐1273 booster versus placebo (solid organ transplant recipients). hImprecision: downgraded one level due to low number of participants.