US researchers have claimed that blood group does not make a person vulnerable to Covid-19 infection nor does it increase the severity, debunking the earlier theories that SARS-CoV-2 infection is linked to certain blood groups.
For the new study, researchers from the University of Utah included more than 11,000 individuals who were newly infected with SARS-CoV-2.
The findings, published in the journal JAMA Network Open, showed that the blood types A, B, AB and O were not associated with disease susceptibility or severity.
Compared with type O blood, type A was not associated with increased viral positivity, hospitalization or ICU admission. Similarly, types B and AB were not associated with worse outcomes than type O.
"Given the large and prospective nature of our study and its strongly nil results, we believe that important associations of SARS-CoV-2 and Covid-19 with ABO groups are unlikely and will not be useful factors associated with disease susceptibility or severity on either an individual or population level for similar environments and ancestries," said the research team led by Jeffrey Anderson, from the varsity's School of Medicine in Salt Lake City.
Earlier, a report from China had suggested that blood group A was linked with increased susceptibility to SARS-CoV-2 infection, while blood group O was associated with reduced susceptibility.
Another set of studies from Italy and Spain reported that blood group A was associated with an increased risk of severe Covid-19 and blood group O was associated with a reduced risk.
In contrast, a large Danish study implicated disease susceptibility but not severity. However, result of studies from Boston, Massachusetts, and New York, did not confirm any specific associations between ABO blood group and disease.
These reports led to widespread interest in examining ABO blood groups as potential Covid-19 risk factors, researchers said.
"The smaller sample sizes and retrospective, observational nature of many prior studies, in addition to their striking heterogeneity of ABO associations with disease susceptibility and severity, could be due to chance variations, publication bias, differences in genetic background, geography and environment, and viral strains," the researchers noted.
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