Back in June, a meta-analysis study across China and the USA investigated the relationship between different blood groups (O, A, B, & AB) and relative risk of COVID-19 infection. Blood group O was found to be protective (odds Ratio 0.73) whilst blood group A was found to have a higher risk (odds Ratio 1.16). A comparable but smaller study across Italy and Spain used genome-wide association analysis, and suggested correlations between the gene locus forblood group and the genes associated with immune response (interleukin-6) and blood coagulation.
This was particularly interesting as those with blood group O are typically more vulnerable to infections, but are more protected against the risk of heart disease. This would be consistent with the central role of ACE2 receptors to the development and progression of COVID-19, given the receptors' role in regulation of blood pressure.
These initial findings sparked a flurry of further research, and two major studies have reported further insights over the last month. A four month study of 1 million volunteers by 23andMe, the direct to consumer genetics insights company, provided clear evidence for the role of blood group on both susceptibility and severity in COVID-19, suggesting a potential link between blood group and the ability of internalise SARS-CoV-2 viral particles. And this last week, a Danish study of almost 500,000 individuals tested for COVID-19 confirmed that those with blood group O experienced a decreased risk of SARS-CoV-2 infection (Odds Ratio 0.67).
All of these studies are highly relevant to current research on the importance of superspreaders to SARS-CoV-2. In vitro studies have suggested that anti-A and anti-B antibodies may be neutralising the virus. The hypothesis put forward previously suggests that virus particles are covered by the ABO antigens of their current host, and hence allow viruses to be rejected by new hosts with an incompatible blood group by the same process as blood transfusions. This would not only explain why those with blood group O are least likely to get infected, but also predict that these "universal donors" would generate the highest number of subsequent infections. It further implies that you should be wary around those with the same blood group as you. The question is - do you know your blood group?