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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 is most susceptible to Covid 19. That link was established pretty early on in the pandemic and scientists didn't let it go. Additional research has buttressed the possibility of a link.
But let's back up first. In 2020, scientists started talking about a link between blood type and Covid. That year, research in the journal PLOS Genetics revealed that people with Type A blood are more likely to have a severe case of Covid-19.
A previous study in the journal Blood Advances from 2020 also affirmed this research, adding that people with Type O blood seem to be more protected from Covid.
Researchers in China first shared this idea in March 2020, 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 who were diagnosed and hospitalized for Covid (this was prior to vaccines), 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 than those with other blood types, while those with Type O were 35 percent less likely.
Where are we now, in 2022, on blood type and Covid? Additional research and review papers have confirmed that we're in more or less the same place: It looks like there really is an association between Type A blood and susceptibility to Covid and Type O blood and less susceptibility. Yet no research so far has been able to pin down the molecular goings on that explain the mechanism behind why this might be so.
"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.
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 difference may be the type of 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 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. And clotting issues—including strokes, kidney failure, and pulmonary embolisms—come up a lot with Covid infections. In addition, a 2020 analysis in The Lancet found that compared to Covid 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 have died at a disproportionately high rate from Covid, tend to have higher levels of VWF, too.
So if I’m O, am I safe from Covid?
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, and 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 risk
People with Type O blood might be slightly more protected from the virus, and people with Type A slightly more vulnerable.
The discovery of Type O’s protective effect is crucial to building an understanding of how the virus works. But both docs agree it shouldn’t actually change anyone’s behavior. Vaccines are still important, as are smart choices to protect yourself from germs.
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