Does blood type really connect with risk of contracting COVID-19?

Some studies have made people wonder if blood type affects coronavirus risk, with a previous study indicating that people with Type A may have a higher risk of catching COVID-19 and developing severe symptoms while people with Type O blood may have a lower risk.

However, a study published this week counters some early findings. Researchers at Massachusetts General Hospital and Beth Israel Deaconess Hospital published a study Thursday (July 16) that found no evidence that blood type affects whether someone develops severe symptoms from a coronavirus infection.

But the study also indicated that patients with blood types B and AB who received a test were more likely to test positive as were those who are Rh+ positive, and blood type O was less likely to test positive.

In addition, Sakthivel Vaiyapuri, an associate professor in cardiovascular and venom pharmacology at the University of Reading in the UK, is conducting a study into the role of blood types based on data from more than 4,000 people in Iraq who had COVID-19 and 4,000 who didn't get sick. He said that early results suggest type O might have a protective effect, but it's not definitive. And given how many underlying variables there are, any effect, protective or otherwise, is likely to be quite small.

For example, Type O blood is more prevalent among African Americans, yet African Americans have experienced disproportionately high infection rates of COVID-19.

"Group O shouldn't think they aren't going to get this disease. They shouldn't be running around everywhere and not maintain social distance, nor should group A panic," Vaiyapuri said.

Unlocking what role blood types play would potentially help scientists better understand the risk of disease for people in different blood groups.

Blood types were discovered in 1901 by the Austrian immunologist and pathologist Dr. Karl Landsteiner, who later won a Nobel Prize for his work. Prior to the discovery of blood groups, a transfusion was a high-stakes process fraught with risk.

Because people's blood types are identified by antibodies, part of the body's natural defense system, and antigens, a combination of sugars and proteins that coat the surface of red blood cells. Once antibodies recognize any foreign antigens, they would tell the immune system to destroy them. That's why giving someone blood from the wrong group can be life-threatening.

Other past research indicates that certain blood groups may affect vulnerability to other diseases, including cancer.

For example, blood type B has been associated with a reduced risk of cancer, while group O has been linked to a lower risk of dying from severe malaria but appeared to be more susceptible to norovirus infection, the winter vomiting bug that also causes diarrhea.