Blood type A associated with critical COVID-19 and death in a Swedish cohort—a critical comment

Excerpt

I read with great interest the letter by Hultström et al. entitled “Blood type A associates with critical COVID-19 and death in a Swedish cohort” [1]. The authors report an association of blood group A with the risk of requiring critical care as well as with an increased risk of death within 30 days. The study is based on the blood group distribution from a Swedish critical care cohort (n = 64) compared to the blood type distribution in the population as a whole. It is stated that this latter study confirms earlier papers on blood type and COVID-19 severity such as a genome-wide association study by Ellinghaus et al. [2] and a clinical/serological study by Zietz and Tatonetti [3] both identifying blood group A as a risk factor for disease severity and death in COVID-19. Nevertheless, the letter gives rise to concerns. …