A study published Wednesday in the New England Journal of Medicine says that patients with blood type A are at increased risk for COVID-19-induced respiratory failure than other blood groups.

Researchers compared the genomes of roughly 1600 people with severe COVID-19 at 7 hospitals in 4 cities in Italy and Spain with over 2200 uninfected population-based controls.

Blood group A was associated with a 45% increased risk for COVID-19 respiratory failure, while blood group O was associated with a 35% lower risk, relative to other blood groups.