Most humans belong to one of these four blood groups: A, B, AB, O, and typically, blood type makes very little difference in daily life, except if you need a transfusion.
MEXICO CITY (CNN) – Scientists around the world have found that people with type A blood may have a higher risk of getting covid-19 and developing severe symptoms, recent research suggests, while people with type O blood have a lower risk. This study’s results follow the evidence from previous research that certain blood groups are more vulnerable to other diseases such as cancer.
It remains mostly unknown why we have different blood types and what purpose they serve, and very little is known about their links to viruses and diseases. Unlocking the role that blood types play could potentially help scientists better understand the risk of illness for people of different blood groups.
Why it matters.
Blood types were discovered in 1901 by Austrian immunologist and pathologist Dr. Karl Landsteiner, who later won a Nobel Prize for his work. Like other genetic traits, blood type is inherited from our parents.
Before discovering blood types, a transfusion, a standard procedure that now saves lives, was a high-risk process. Pioneering physician James Blundell, who worked in London in the early 1800s, gave blood transfusions to 10 of his patients, and only half survived.
What was not known was that humans should only obtain blood from certain other humans.
The ABO blood grouping system is identified by antibodies, part of the body’s natural defense system, and antigens, a combination of sugars and proteins that cover the surface of red blood cells. The antibodies recognize any foreign antigen and tell your immune system to destroy it. That’s why giving someone blood from the wrong group can be life-threatening.
For example, I have type A+ blood. If a doctor accidentally injected me with type B, my antibodies would reject it and work to break down the foreign blood. As a result, my blood would clot, disrupt my circulation, bleed and breathe hard, and potentially die. But if I received type A or type O blood, I would be fine.
Your blood type is also determined by your Rh status, an inherited protein found on the surface of red blood cells. If you have it, you’re positive. If not, you’re negative.
Most people are Rh-positive, and they can get blood from compatible blood types that are either negative or positive. But people with Rh-negative blood usually should only get Rh-negative red blood cells (because their antibodies can react with the incompatible donor).
That leaves us with eight possible primary blood types, although there are some rarer ones.
In the center of each figure are the donors, and on the edges are the possible recipients. As we can see, type O negative blood can be used in transfusions to people with any type of blood.
Not only humans have blood types, at least 17 different types of primates as well, including chimpanzees and gorillas. Evolutionary biologists have discovered that blood types are ancient, dating back 20 million years to a distant ancestor that we share with primates. “Many primate species … also have the differences of being A, being B, being AB,” Segurel said. “Whether it’s a great ape or a new ape, it’s quite curious that differences have been found or maintained in so many different species,” he added.
The ABO blood type gene doesn’t just influence our blood. It is also active in the wider variety of tissues and organs, including our digestive or respiratory system. This can be important when our bodies face infections with different blood types that offer us protection against various pathogens and diseases.
For example, blood type B has been associated with a reduced risk of cancer. In contrast, group O has been associated with a reduced risk of dying from severe malaria, but it appears to be more susceptible to norovirus. This winter vomiting virus also causes diarrhea.
A team of European researchers published their findings in the New England Journal of Medicine in June. They found that people with type A blood had a 45% greater risk of becoming infected than people with other blood types, and people with type O blood were 65% more likely to become infected than people with different blood types. They studied more than 1,900 severely ill coronavirus patients in Spain and Italy and compared them to 2,300 people who were not sick.
A similar effect was seen in Hong Kong health workers with blood type O during the SARS outbreak, which infected 8,098 people from November 2002 to July 2003 from the same virus family.
There are two hypotheses about the link between blood groups and covid-19, said Jacques Le Pendu, director of research at Inserm, a French medical research organization. One is that people with type O are less prone to clotting problems, and clotting had been a significant factor in the severity of covid-19 cases.
Le Pendu said it could also be explained by the likelihood that the virus carries the antigen of the infected person’s blood type. As such, antibodies produced by a person with blood type O can neutralize the virus when infected by a person with blood type A, similar to the rules for blood transfusions. “However, this protective mechanism would not work in all situations. A person with blood type O could infect another person with blood type O, for example,” he explained, adding that any protective effect is unlikely to be great and that antibody amounts are highly variable from person to person.
“People with type A should not be alarmed. People with type O should not relax”, said Sakthivel Vaiyapuri, an associate professor of cardiovascular pharmacology at the University of Reading in the United Kingdom.
Vaiyapuri, in collaboration with Thi-Qar University in Iraq, is conducting a study of the role of blood types based on data from more than 4,000 people in Iraq who had covid-19 and 4,000 who did not become ill. He said early results suggest that type O might have a protective effect, but that is not definitive. And given the number of underlying variables that exist, it’s likely that any result, protective or not, is quite small.
For example, the idea that having type O blood is protective is not consistent with covid-19 infections in the United States. Type O blood is more common among black people, who have experienced disproportionately high rates of disease.
“People in group O should not think that they will not get this disease. They shouldn’t be running around and not keeping social distance, (just as) group A shouldn’t panic,” he said. “There are so many underlying factors. We think of this as a respiratory virus, but it’s a whole collection of things that are happening that we don’t yet understand,” he said.
Blood-type research has sometimes fallen into different academic disciplines. Still, a better understanding of why we have different blood groups and the relationship between blood-type antibodies and disease risk will likely help us develop vaccines and design new drugs, even for covid-19.