An intriguing study published last week found a link between covid-19 severity and having type A blood; type O blood, on the other hand, was linked to a lower chance of severe illness. But it’s unlikely that any potential connection between covid-19 and blood type will be very relevant to the average person.
The study, published in the New England Journal of Medicine, involved nearly 2,000 severely ill covid-19 patients in Spain and Italy. Researchers looked at these people’s genetic code, in what’s known as a genomewide association study, or GWAS. They compared their genetics to the genetics of a similar control group, looking for any differences that could plausibly influence someone’s risk of catching the infection or having a more serious case.
They ultimately found two possible regions of genes and several genetic variations associated with covid-19. One region seems to play a role in our immune response to infection and is also connected to the angiotensin-converting enzyme 2 (ACE2) protein, which is produced by the surface of many cells. That makes plenty of sense, given that the coronavirus infects our cells through the receptors for ACE2.
They also found an association between covid-19 and a region of genes that influences our blood type. And when they looked at the patients themselves, they found a clear link there as well. People with type A blood were found to have a 45 percent greater risk of contracting severe covid-19 compared to non-type A patients, while people with type O blood seemed to have a 35 percent lower risk of severe infection compared to non-O types. While those percentages may sound huge, it remains true that most people who contract the coronavirus will not become sick enough to need hospitalization, regardless of blood type.
The findings aren’t implausible, as blood type and genetics are already suspected to affect our risk of suffering from all sorts of medical conditions. The researchers laid out several hypotheses for how blood type could affect our vulnerability to infection, including its effects on proteins that help regulate clotting (severe covid-19 is known to cause heavy clotting of the blood).
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But there are a few important limitations here, according to Eric Gehrie, an assistant professor of pathology at the Johns Hopkins University School of Medicine who is also the medical director of Johns Hopkins Hospital’s blood bank.
Right off the bat is that no single study’s findings should be taken as the final word on a subject. This seems to be the first major published GWAS research of its kind, and similar studies on different groups of people would have to confirm the genetic links found here.
Gehrie noted that the authors weren’t able to account for other factors that may explain the link between blood type and covid-19 severity, as they readily admit.
“If it turned out that more people who are type A in the study had some other risk factor for coronavirus, like they were immunocompromised, then this methodology wouldn’t be able to pull that information in,” Gehrie told Gizmodo. “And I’m not criticizing the study—they did a outstanding job in collecting all this data across the world in so short a time. But the nature of this kind of research is that it’s not definitive; it’s hypothesis-generating.”
There’s also the history of medical research involving blood types to consider, Gehrie said. Studies have linked certain blood types to a greater risk of developing dozens of diseases and medical conditions, which range from the very serious, such as heart attacks, to the mundane, such as mosquito bites. But when you look deeper into these connections, they don’t matter much in the grand scheme of other things that make someone prone to getting sick.
“Everybody knows that regardless of your blood type, anybody can develop coronary artery disease. And regardless of your blood type, anybody can be bitten by a mosquito,” Gehrie said. “So now we have this information saying that based on your blood type, you might have a difference in risk for coronavirus. And I would just say, proceed with extreme caution.”
Right now, we don’t know how much a person’s blood type contributes to their risk of serious illness from coronavirus. Other well-known risk factors, such as age and pre-existing health problems like type 2 diabetes, will likely continue to matter much more than blood type, including to doctors treating these patients.
“It’s a big headline, but scientifically, if one of my colleagues in the emergency room were to call me up and say, ‘Hey, we were about to intubate somebody, but then we noticed their blood group was O. Should we still do it?’ I’d be like, ‘You’re crazy. You’re just absolutely crazy,’” Gehrie said.
The same logic applies to the genetics findings in the new research. A person’s genetic risk for any disease is absolutely important to study, but a lot of the time, it pales in comparison to other, non-genetic risk factors. For example, some people are more genetically predisposed to develop diabetes, but the genetic component of their risk is tiny compared to things like diet and exercise. In the case of covid-19, being genetically “lucky” is probably going to matter far less than simply avoiding crowded spaces, if you’re hoping to avoid a serious infection.
The authors of this new study don’t appear to include any absolute risk estimates. But preliminary findings from a study earlier this year, using 23andMe data, offer some related context. Within their sample, 1.3 percent of people with type O blood had tested positive for covid-19—a mere 0.2 percent difference from people with type B or AB blood. Of people with type A blood, 1.4 percent tested positive, which seems to somewhat conflict with the NEJM data but ultimately may not mean anything, either.
None of this means that blood type or genetics won’t be important areas of covid-19 research. It just means that you shouldn’t consider yourself doomed because you have type A blood, and you definitely shouldn’t think that you’re impervious because you have type O blood.
For his part, Gehrie wishes that people were more concerned with an actual urgent problem involving blood types that’s been worsened by the pandemic: blood donation.
“The biggest issue we have with blood types right now is that we’re extremely short of blood, and we are literally scraping the bottom of the barrel, inventory wise,” he said. “So I hope that people who are eligible would consider donating, because cancer, sickle cell disease, bone marrow transplants, etc—those things don’t care that covid-19 is going on. And the people who have those diseases still have them.”