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Systematic review and meta-analysis of the effect of ABO blood group on the risk of COVID-19 infection

We have been experiencing a global pandemic with baleful consequences
for mankind, since the Severe Acute Respiratory Syndrome Coronavirus 2
(SARS-CoV-2) was first identified in Wuhan of China, in December 2019. 
So far, several potential risk factors for SARS-CoV-2 infection have
been identified. Among them, the role of ABO blood group polymorphisms
has been studied with results that are still unclear. The aim of this
study was to collect and meta-analyze available studies on the
relationship between SARS-CoV-2 infection and different blood groups, as
well as Rhesus state. We performed a systematic search on PubMed/MEDLINE
and Scopus databases for published articles and preprints. Twenty-two
studies, after the removal of duplicates, met the inclusion criteria for
meta-analysis with ten of them also including information on Rhesus
factor. The odds ratios (OR) and 95% confidence intervals (CI) were
calculated for the extracted data. Random-effects models were used to
obtain the overall pooled ORs. Publication bias and sensitivity analysis
were also performed. Our results indicate that blood groups A, B and AB
have a higher risk for COVID-19 infection compared to blood group O,
which appears to have a protective effect. An association between Rhesus
state and COVID-19 infection could not be estabished.