Two recently published studies, in the journal Blood Advances, added to the growing evidence linking blood type and severe COVID-19.
In early March, researchers in China looked at the blood group distribution of over 2,000 hospitalized patients from across Wuhan and Shenzhen. They found a higher prevalence of blood type A in COVID-19 patients. However, the study was found to have multiple limitations. Researchers, therefore, suggested additional research to establish a link.
Since then, multiple studies have looked at the link between the blood type and the risk of contracting severe COVID-19. Most recently, two studies, one from Denmark and another from Canada, have found evidence for the hypothesized risk.
Prevalence of Blood Type O in the Danish Population
Scientists in Denmark conducted a retrospective cohort study on all Danish individuals tested for SARS-CoV-2 between February and July 2020. The blood type of these 473 654 individuals was compared to a control group comprising of 2.2 million untested individuals.
It was discovered that fewer people with blood group O caught COVID-19, which is around 38%. Whereas, 44% of the COVID-19 patients had blood type A compared to just 42% of the Danish population.
We do not know whether this is some kind of protection of group O, or whether it’s some kind of vulnerability in the other blood groups
Dr. Torben Barington, the senior author of the Danish paper
84% of Blood Group A Required Mechanical Ventilation
In the second study, Canadian researchers investigated data from 95 critically ill patients hospitalized with COVID-19 in Vancouver, Canada.
The study found those with blood type A or AB required a longer stay in the ICU (intensive care unit), as compared to those with blood group O. Furthermore, 61% of the patients with blood group O or B required mechanical ventilation, as compared to 84% in blood group A or AB.
As a clinician … it is at the back of my mind when I look at patients and stratify them. But in terms of a definitive marker we need repeated findings across many jurisdictions that show the same thing
Dr. Mypinder Sekhon, author of the Canadian study.
While evidence for the hypothesis has definitely been growing, researchers argue a causal relationship has yet to be established between blood groups and the risk of severe COVID-19.
Reference:
Mike Bogetofte Barnkob, et al. Reduced prevalence of SARS-CoV-2 infection in ABO blood group O. Blood Adv 2020; 4 (20): 4990–4993. doi: https://doi.org/10.1182/bloodadvances.2020002657
Ryan L. Hoiland, et al. The association of ABO blood group with indices of disease severity and multiorgan dysfunction in COVID-19. Blood Adv2020; 4 (20): 4981–4989. doi: https://doi.org/10.1182/bloodadvances.2020002623
Shelton, J. F., et al. (2020). Trans-ethnic analysis reveals genetic and non-genetic associations with COVID-19 susceptibility and severity. doi:10.1101/2020.09.04.20188318
