Question: I’ve been reading that some blood types are more at risk for contracting a severe version of the virus than others, was wondering if you could touch on this with more data? What I’m seeing is that people with Blood Type A are the most at risk and people with Blood Type O are the least.

Answer:I’m glad you asked. I had read some initial news reports about this finding a few weeks ago when the paper was a pre-print and then I set it aside to wait for the paper to be peer-reviewed. And now it has been! Published a few days ago, findings suggest that people with blood type A have higher odds of severe disease (45% increase in odds) than people with other blood types; people with blood type O have lower odds of severe disease (35% decrease in odds) compared with people of all other blood types. Let me give you an overview of the study and then some context regarding the blood type finding. One thing I want to note is that the difference in severity isn’t due to the form of virus contracted (e.g. a “more severe version”), but rather in how the body responds to the virus itself (e.g. a “more severe outcome”). So far, we do not have solid evidence about COVID-19 mutations causing more/less severe outcomes. Finally, if you have Blood Type O, do not rejoice — Lower odds does not mean no risk! Similarly, if you have Blood Type A, do not despair — Higher odds does not mean severe disease is a given!

Research overview: The new research, conducted by a group of scientists called the Severe COVID-19 GWAS Group (here, GWAS is Genome-Wide Association Study), was published in the New England Journal of Medicine a few days ago. Basically, in the search to understand why some people suffer more severe outcomes from the virus, this group of scientists turned to a relatively new study form — genome-wide association study. The scientists used the GWAS methodology to search people’s genes for small variations, called single nucleotide polymorphisms or SNPs (pronounced “snips”), that occur more frequently in people with a given disease compared to people without the disease. Here, the disease is severe COVID, defined as respiratory failure that necessitates use of oxygen therapy or ventilator support. The group compared the genomes of 1,980 study participants in Italy and Spain who had severe COVID with the genomes of 2,381 control participants in Italy and Spain whose infection status was unknown. The researchers found two gene clusters associated with severe COVID: Cluster 1 is involved in the regulation of the immune response, especially in the lungs, and Cluster 2 is involved in determining the ABO blood group type. When the scientists recognized Cluster 2’s relationship to blood type, they analyzed outcomes by blood type, controlling for age and sex, and found “a higher risk among persons with blood group A than among patients with other blood groups (odds ratio, 1.45; 95% CI, 1.20 to 1.75; P=1.48×10−4) and a protective effect for blood group O as compared with the other blood groups (odds ratio, 0.65; 95% CI, 0.53 to 0.79; P=1.06×10−5).” The authors further posit in the discussion section that blood group A may be more susceptible to acquiring the virus, but this is not a finding directly borne out in the data they present, so I wouldn’t put much weight in that component of the paper. As far as GWAS studies go, this one was quick and relatively small. Most (all?) scientists are waiting on more data before embracing the finding that blood type impacts disease severity. Indeed, the NIH is currently funding a set of researchers to use GWAS to study gene variants among 5,000 COVID patients in the US and Canada. That said, there is a body of science that supports the link between blood type and severity of other forms of disease, including other coronaviruses. And recent research out of Wuhan, “Association between ABO blood groups and risk of SARS-CoV2 pneumonia”, also supports the blood type findings. And if you want to explore blood type differences further, the Australian Academy of Science offers a really nice, easy to read synthesis (Figure 1).

Figure 1. Blood Type Differences (from: Australian Academy of Science)