There's more evidence that blood type may affect a person's risk for COVID-19 and severe illness from the disease.
The findings are reported in a pair of studies published Oct. 14 in the journal Blood Advances.
In one, researchers compared more than 473,000 people in Denmark with COVID-19 to more than 2.2 million people in the general population.
Among the COVID-19 patients, there was a lower percentage of people with blood type O and higher percentages of those with with types A, B and AB.
The findings suggest that people with A, B or AB blood may be more likely to be infected with COVID-19 than people with type O blood. Infection rates were similar among people with types A, B and AB blood.
The other study included 95 critically ill COVID-19 patients hospitalized in Canada. Patients with type A or AB blood were more likely to require mechanical ventilation, suggesting that they had greater rates of lung injury from COVID-19.
More patients with type A and AB blood required dialysis for kidney failure, the study added.
The results suggest that COVID-19 patients with A and AB blood types may have an increased risk of organ dysfunction or failure than those with type O or B blood, according to the researchers.
They also found that while people with blood types A and AB didn't have longer overall hospital stays than those with types O or B, on average, they were in intensive care longer, which may indicate more severe COVID-19.
"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," said study author Dr. Mypinder Sekhon, a clinical instructor in the Division of Critical Care Medicine at the University of British Columbia in Vancouver, Canada.
"Of particular importance as we continue to traverse the pandemic, we now have a wide range of survivors who are exiting the acute part of COVID-19, but we need to explore mechanisms by which to risk stratify those with longer-term effects," he added in a news release.
The U.S. Centers for Disease Control and Prevention has more on COVID-19.