Blood type doesn’t affect much in our daily lives. In fact, most people don’t even know whether they’re Type A, B, AB, or O. But the seemingly-banal detail might be a factor in who comes under the thumb of 2020’s world-wide tyrant—that is, coronavirus.
A new study in the journal Blood Advances backs up what researchers have been seeing for a while: People with Type A blood are at a much higher risk for contracting COVID-19 while people with Type O seem to be more protected from it, according to a growing body of research.
Researchers in China first shared this idea back in March, and the findings were echoed by a paper out of Columbia University a month later. Even DNA testing company 23andMe tapped their customers and found that among 750,000 people (by far the biggest study population yet) who were diagnosed and hospitalized for COVID-19, those with type O were more protected.
Then, a study published in the New England Journal of Medicine confirmed the idea with a peer-reviewed study: Folks with Type A blood were 45 percent more likely to become infected with COVID-19 than those with other blood types, while those with Type O were 35 percent less likely.
“It’s pretty clear that Type O is protective to some degree. I don’t think that having Type A or Type B is the problem—it’s just that they don’t have Type O,” says Mark Udden, MD, professor of hematology and oncology at Baylor College of Medicine in Houston.
Are people with Type A blood more likely to die from COVID-19?
So people with Type A may be more likely to catch the virus, but whether they also get it worse is still unclear: the NEJM study reports that people with Type A blood were also more likely to have respiratory failure.
However, the research out of Columbia University found there wasn’t really any difference among intubations or death and different blood types. And a recently released study in the Annals of Hematology looked specifically at the link between blood types and the need for intubation or death in confirmed COVID-19 patients. They found no link between blood type and the severity of the illness. The new research in Blood Advances, mentioned above, had similar findings. Although true to the unending questions aroung this new disease, another, smaller study, also in Blood Advances, suggested that blood types A or AB had higher risk of certain intense interventions and longer ICU stays, but the researchers themselves considered the link to be so far “unresolved.”
What’s different about Type O?
We don’t know why people with Type O might possibly be more protected—but there are a lot of theories.
The most basic idea is that blood type might influence a person’s ability to fight the virus, says David Aronoff, M.D., director of the division of infectious diseases at Vanderbilt University Medical Center in Nashville. It may affect your immune system’s strength or your inflammatory response to the infection.
Either way, that would color how likely you are to not only get the virus but also how strong your symptoms are, he explains.
The NEJM paper, however, highlights the antibodies we produce depending on blood type. “If you’re type O, you naturally make antibodies against Type A and Type B,” Dr. Udden says. These Type A antibodies might make it more difficult for SARS-CoV-2 to attach to its receptor in Type O blood and multiply in the body, he explains.
But there’s another interesting layer to a potential protective element in Type O blood: something called von Willebrand factor, which is a glycoprotein in charge of repairing damage to blood vessels by prompting your blood to clot.
We know the COVID-19 virus damages the lining of your blood vessels. Your body then releases von Willebrand factor, or VWF, into your blood so it can fix the damage to the vessel walls. But VWF also encourages clotting.
“In COVID-19 patients who die, we’re seeing unusually high clotting issues, like strokes, kidney failure, and pulmonary embolisms—so we know there is a clotting problem that stems from the virus,” Dr. Udden says.
A recent analysis in The Lancet found that compared to COVID-19 patients who weren’t in intensive care, those who were critically ill in the ICU and died had higher VWF antigens in their blood.
And guess what: People with Type A blood have higher levels of VWF naturally than people with type O blood, Dr. Udden points out. In addition, people who are Black, who are dying at a disproportionately high rate from COVID-19, tend to have higher levels of VWF, too.
So if I’m O, am I safe from the coronavirus?
Just because you’re Type O doesn’t mean you’re in the clear. All studies so far have only looked at blood type in connection to symptomatic cases of coronavirus, Dr. Aronoff points out.
We don’t know about asymptomatic carriers—that is, Type O could still pass along the virus to other people unknowingly just as much as Type A could.
“There are two possibilities: You’re Type O so you might not contract the virus because it has no landing strip—there’s nothing to attach to,” Dr. Udden explains. “Or by being Type O, the virus gets in but the A antibody prevents it from docking with enough cells to cause disease. But the virus is still in your system and you can still pass it to someone else.”
Is blood type the main risk factor?
No. Blood type is actually a pretty weak player, Dr. Udden says.
Socio-economic status is a big vulnerability—likely to need to work outside the home, in crowded buildings, and living in tighter quarters with more family members.
Age and health are next in line for susceptibility. If you’re older or have an underlying disease like cancer, diabetes, or heart disease, you’re more likely to develop a severe case of coronavirus, Dr. Udden adds.
Blood type is after all of these.
The bottom line on blood type and COVID-19 risk
People with Type O blood might be slightly more protected from the virus, and people with Type A slightly more vulnerable. But, as far as we know, everyone is still at risk of getting the virus, and definitely at risk of being an asymptomatic carrier—and therefore of spreading it to others.
The discovery of Type O’s protective effect is crucial to building an understanding of how the virus works—especially considering there aren’t many other patterns it follows, Dr. Udden points out.
But both docs agree it shouldn’t actually change anyone’s behavior.
“I’m Type O, and I’m not going to go hang out in bars just because of this slight protective effect,” Dr. Udden says.
“These findings shouldn’t change your behavior. Anyone can still get ill with SARS-CoV-2 and/or participate in the chain of transmission,” Dr. Aronoff adds.
The bottom line is clear: The safest and most effective way to prevent from getting coronavirus or unknowingly spreading it to others is to keep wearing a mask and socially distancing from people—regardless of your blood type.