So far, age, gender and comorbidities have been considered determinants of the COVID-19 disease’s progression. Now, an unexpected factor seems to be influencing susceptibility to COVID-19, according to two recent studies: blood type.

In both studies published in the journal Blood Advances last week, researchers said that people with blood type O could be less vulnerable to the disease than people with other blood types.

While the outcome of the two research papers was the same, there were a few differences worth noting. The Danish study said that more COVID-19 positive people had blood types A, B and AB, while fewer people with blood type O tested positive with the coronavirus infection.

On the other hand, the Canadian study demonstrated that, along with blood type O, even blood type B seemed to provide some immunity against the novel coronavirus and its complications. According to the study, more people with types A and AB required treatment, especially when compared to blood groups O or B. More people in the former category also underwent treatment at intensive care units (ICUs) with ventilators for potential lung damage and dialysis for kidney malfunction.

Nevertheless, the authors maintained further research is needed to establish a cause and effect relationship between blood type and susceptibility. More importantly, previous studies published earlier this year found that belonging to a particular blood group does not mean that one should be any less careful against COVID-19, and cautioned against relaxing vigilance.

Danish Research

Both the Danish and the Canadian studies compared people with COVID-19 to control groups -- which always lends accuracy to a study. The studies compared cases to national registries in their respective countries of people without COVID-19, including their blood groups.

In the Denmark study, 7,422 individuals who tested positive between Feb. 27 and July 30, 2020, were weighed against 38% of Denmark’s population who were not tested for SARS-CoV-2 infection. “Among the SARS-CoV-2 individuals, considerably fewer [blood] group O individuals were found; conversely, more A, B, and AB individuals were noted. When blood group O was excluded, no significant difference was seen among A, B, and AB,” the paper explained.

According to the researchers based in Denmark, blood groups did not figure as a risk factor when it came to assessing hospitalization and death due to COVID-19. Similarly, age, comorbidities and not working in the health sector did not explain the advantage enjoyed by blood group O individuals, making this correlation a bit of a medical mystery for the time being.

“Our findings of similar relative protection by blood group O in young individuals, in health care personnel, and in individuals without a registered cardiovascular diagnosis suggest that associations between non-O blood groups and comorbidities do not explain the apparent protection enjoyed by group O individuals,” the paper said.

Henceforth, more research may be able to throw some light on why this happens.

The Canadian Paper

In the study based in Vancouver, Canada, 125 patients admitted to the ICU in six metropolitan Vancouver hospitals from March 1 to April 28, 2020, were analyzed. Of those patients, 95 had the required information on their blood groups. For the sake of establishing contrasting factors, these participants were then divided into two groups: those who had blood group O or B and others with blood group A or AB respectively.

The following are the study’s findings:

  • People belonging to blood groups A and AB needed more medical attention.
  • From blood groups A and AB, about 84% required a ventilator to help them breathe. However, among people with blood groups O and B, 61% required the same.
  • Among A and AB patients, about 32% needed dialysis, a treatment that supports kidney function when the kidneys are failing. Not as many patients with blood groups O and B needed dialysis.

"The unique part of our study is our focus on the severity effect of blood type on COVID-19. We observed this lung and kidney damage, and in future studies, we will want to tease out the effect of blood group and COVID-19 on other vital organs," Mypinder S. Sekhon, MD, of the University of British Columbia, said in a news release.

On the contrary, another study published in the Annals of Hematology this July said disease severity could not be predicted by blood groups. “We showed through a multi-institutional study that there is no reason to believe being a certain ABO blood type will lead to increased disease severity, which we defined as requiring intubation or leading to death,” Anahita Dua, assistant professor of surgery at Massachusetts General Hospital and senior author, said in a news release.

Seema Prasad is a freelance health reporter based in Bengaluru, India. She tweets @SeemaPrasad_me