CHICAGO (NewsNation Now) — Two new studies suggests that people with blood type O may be less likely to contract coronavirus and have milder symptoms if they do become infected. It’s not clear yet what causes the statistical connection found in the studies released Wednesday.

The studies were both published in the journal Blood Advances, a publication of the American Society of Hematology. A Danish study found that among 7,422 people who tested positive for Covid-19, only 38.4% were blood type O, despite people in that blood group making up 41.7% of the roughly 2.2 million untested people in the population.

However, those with type A blood made up 44.4% of the infected patients, the study found. The wider Danish population that blood type makes up 42.4%.

The Canadian study looked at 95 patients who became critically ill with COVID-19 and examined their outcomes. Those with type A or type AB ended up needing treatment with a ventilator, compared to 61% when it came to patients with type O or B.

“A higher proportion of Covid-19 patients with blood group A or AB required mechanical ventilation and had a longer ICU stay compared with patients with blood group O or B,” the study finds.

Those with type A or AB blood had a median stay in the intensive care unit of 13.5 days, compared to 9 days for those with type O or B.

NewsNation interviewed Dr. Amesh Adaljaa, a senior scholar at the Johns Hopkins University Center for Health Security. Watch the full interview in the player above.

There are four major blood groups: A, B, AB or O. In the U.S. the most common blood groups are O and A.

Nexstar Media Wire contributed to this report.