Table II.
Summary of findings table. Relationship between ABO blood group and occurrence and severity of COVID-19
| Patient or population: COVID-19 infected subjects and uninfected controls. Settings: Inpatients and Outpatients. Comparison: ABO prevalence among COVID-19 infected and non-infected individuals; ABO prevalence in patients with severe or non-severe COVID-19 infections. | ||||||
|---|---|---|---|---|---|---|
| Outcomes | Illustrative comparative risks* (95% CI) | Relative effect (95% CI) | N. of Participants (studies) | Quality of the evidence (GRADE) | Comments | |
| Assumed risk | Corresponding risk | |||||
| Non-O group | O group | |||||
| Overall comparison | 382,537/892,496 (42.8%) | 34.6% (32.1/36.8%) | OR, 0.81 (0.75/0.86) | 922,145 (16; 18 cohorts) | ⊕⊝⊝⊝ very low1 |
There was evidence that individuals with blood group 0 had a decreased risk of SARS-COV-2 infection |
| Case-control studies | 81,183/184,966 (43.8%) | 31.9% (28.0/36.3%) | OR, 0.73 (0.64/0.83) | 193,112 (10; 12 cohorts) | ⊕⊝⊝⊝ very low1 |
There was evidence that individuals with blood group 0 had a decreased risk of SARS-COV-2 infection |
| Cohort studies | 301,354/707,530 (42.5%) | 37.8% (36.1/39.9%) | OR, 0.89 (0.85/0.94) | 729,033 (7) | ⊕⊕⊝⊝ low2 |
There was evidence that individuals with blood group 0 had a decreased risk of SARS-COV-2 infection. However, compared to case-control studies, the magnitude of the effect size in cohort studies was significantly lower |
| Severity of infections (endpoint severe infection/ICU admission) | 1,083/5,541 (19.5%) | 19.5% (17.7/21.2%) | RR, 1.00 (0.91/1.09) | 9,147 (7) | ⊕⊕⊝⊝ low3 |
Overall, individuals with blood group 0 had the same risk of severe SARS-CoV-2 infection compared to individuals with non-0 blood group |
The assumed risk is the mean control group risk across studies. The corresponding risk (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).
Downgraded for inconsistency due to heterogeneity, and twice for risk of bias in case-control studies (confounding, selection, ascertainment);
downgraded twice for inconsistency, and because not all the studies performed matching or adjustment of plausible prognostic variables;
downgraded for imprecision (95% CI includes line of no effect), and because not all the studies adjusted for prognostic factors
GRADE Working Group grades of evidence
High quality: Further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: Further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: Further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: We are very uncertain about the estimate. CI: confidence interval; RR: risk ratio.