Several studies have identified a possible association between ABO blood group and COVID-19. However, studies are of variable quality and results are inconsistent. The aim of this systematic review was to synthesize the evidence on the association between ABO and the risk of COVID-19 infection and prognosis. Searches were conducted in PubMed, MedRxive and BioRxive to identify observational studies published up to May 2021. The incidence of COVID-19 and, among the COVID-19 positive patients, the risk of hospitalization, ICU admission, mechanical ventilation and mortality were also analyzed. A total of 63 studies were included, with 6,470,438 participants. Group O was associated to a significantly lower risk of COVID-19 infection (OR O vs non-O 0.88 95%CI: 0.82–0.94; I²: 91%) and group A with a higher risk (OR A vs non-A 1.08 95%CI: 1.02–1.15). No effect of ABO on the risk of hospitalization, ICU admission or ventilation was observed. Group A was associated with higher mortality (OR A vs non-A: 1.13 95%CI 1.03–1.13), group B with lower mortality (OR B vs non-B 0.88; 95%CI 0.80–0.96), and no effect with group O was observed. The quality of the evidence was rated as “very low” and “low”. Group O would present a reduced risk of COVID-19 infection, but would not influence the prognosis of the disease. Group A would be risk factor for COVID-19 infection and mortality. Group B would not modify the risk of COVID-19 infection, but would be associated to a lower mortality risk.

Drug allergy alert systems (DAAS), have been considered an effective strategy to reduce preventable adverse drug events (ADEs), improving patient's safety. To date, no review has been conducted analyzing characteristics of DAAS in the hospital setting. Therefore, the aim of this study is to identify, describe and summarize the DAAS used in hospitals. The secondary objectives are to analyse drug allergy alerts (DAA) characteristics, the override rate (OvR) and the clinical consequences of alert overrides. Searches were conducted in Medline and Cochrane Library to identify studies describing DAAS. Systems characteristics, generated alerts, DAA, OvR, and its clinical consequences were extracted and analyzed. Twenty-eight articles were included in the review. Seventeen different electronic DAAS were identified, of which 53% were commercially available. Systems differed in drug allergy information and rules for generating alerts. DAA were generally interruptive, triggered by non-exact match at drug prescribing and when ignored, an override reason was mandatory. The OvR ranged from 43.7% to 97%. The main override reason given by providers was that 'patient had previously tolerated or had taken the drug without allergic reaction'. Clinical consequences of overriding DAA were only analyzed in four studies, with an ADE incidence between 0% and 6%. Different DAAS are used in hospitals with some degree of heterogeneity. Accurate and updated drug allergy information is important to generate only high value alerts. A regular review of DAAS and a standardization of alert rules, alert information and override reasons are necessary to optimize systems. Future studies should evaluate the impact of the DAAS aspects on preventing ADEs.