CNN  — 

Most humans fall into one of four blood groups — A, B, AB or O.

Ordinarily, your blood type makes very little difference in your daily life except if you need to have a blood transfusion.

However, some studies have people wondering if blood type affects coronavirus risk. One, for instance, suggests that people with Type A may have a higher risk of catching Covid-19 and of developing severe symptoms while people with Type O blood may have a lower risk.

A study published this week counters some these early findings, a reminder that scientific discovery is an evolving process. Researchers at Massachusetts General Hospital and Beth Israel Deaconess Hospital published a study Thursday that found no evidence that blood type affects whether someone develops severe symptoms (defined as intubation or death) from a coronavirus infection.

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

Why they matter

Why we have blood types and what purpose they serve is still largely unknown, and very little is known about their links to viruses and disease.

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

“I think it’s fascinating, the evolutionary history, even though I don’t think we have the answer of why we have different blood types,” said Laure Segurel, a human evolutionary geneticist and a researcher at the National Museum of Natural History in France.

Blood types were discovered in 1901 by the Austrian immunologist and pathologist Dr. Karl Landsteiner, who later won a Nobel Prize for his work. Like other genetic traits, your blood type is inherited from your parents.

Prior to the discovery of blood groups, a transfusion, a now common lifesaving procedure, was a high-stakes process fraught with risk. Pioneering physician Dr. James Blundell, who worked in London in the early 1800s, gave blood transfusions to 10 of his patients — only half survived.