Variations at two spots in the human genome are associated with an increased risk of respiratory failure in patients with Covid-19, the researchers found. One of these spots includes the gene that determines blood types.

Having Type A blood was linked to a 50 percent increase in the likelihood that a patient would need to get oxygen or to go on a ventilator, according to the new study.

The study was equally striking for the genes that failed to turn up. The coronavirus attaches to a protein called ACE2 on the surface of human cells in order to enter them, for example. But genetic variants in ACE2 did not appear to make a difference in the risk of severe Covid-19.

The findings suggest that relatively unexplored factors may be playing a large role who develops life-threatening Covid-19.