Quite a bit of research has been published lately about blood type and COVID-19 risk. Here, experts weigh in on what you really need to know.

By Korin Miller
October 16, 2020
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Quick, what's your blood type? If you don't know, you're not alone: Fewer than 57% of all Americans know their blood type, according to a 2019 survey from Quest Diagnostics. But now, more people may be scrambling to get that information as research continues to suggest a link between COVID-19 susceptibility and certain blood types.

Right off the bat, it's important to clarify that much more research is needed, and that even with more research, there's not a whole lot the average person can do about these findings. That said, that the data collected over the past few months suggest that certain blood groups—specifically that people with type O blood, or type A or type AB blood—may be either more or less vulnerable to coronavirus infections or severe illness from the disease.

There's a lot to cover here—including what a blood type is, what exactly the research says, and what the information can mean for the public—but here's what doctors want you to know right now.

What is a blood type?

Blood types are split up into four major groups, all dependent on the presence or absence of two certain antigens on the surface of the blood: A and B, according to the American Red Cross. A protein called the Rh factor can also be present (+) or absent (-) from the blood. Those two factors make up the eight most common blood types: A+, A-, B+, B-, O+, O-, AB+, and AB-.

While it's always helpful to know your blood type, the average person won't necessarily need to know that information. Knowledge of your blood type is usually only important if you're undergoing a blood transfusion or organ transplant—but in those situations, your medical team will test your blood type beforehand. It's also helpful to know your blood type—specifically the Rh factor–during pregnancy, so your doctor can troubleshoot if the unborn baby has a different Rh factor.

What does the research say about the link between COVID-19 and blood type?

There's actually a fair amount of research on this topic at this point. The most recent studies were published in the journal Blood Advances, both on October 14.

The first study, conducted by Danish researchers, analyzed data from 7,422 people in Denmark who tested positive, and compared that to blood type information available for 2,204, 742 people in Denmark (those people were not tested for COVID-19). Of the people who tested positive for COVID-19, 38.4% had type O blood—that's compared to 41.7% of the entire Danish population having type O blood. Conversely, 44.4% of those who tested positive for COVID-19 had type A blood, while only 42.4% of the Danish population has that blood type. It was through these findings, that the Danish researchers suggested "that blood group O is significantly associated with reduced susceptibility to SARS-CoV-2 infection."

The second study, this time from researchers in Canada, looked at data from 95 patients who were severely ill with COVID-19. Of those, 84% had either type A or AB blood and required mechanical ventilation. By comparison, only 61% of people with type O or B blood needed the same high level of intervention. It was this data that led Canadian researchers to suggest that those with type A or AB blood were at a higher risk of greater disease severity or requiring mechanical ventilation than those with type O or B blood.

Those two studies were preceded by an earlier study, first published in the The New England Journal of Medicine in June, which looked at data from 1980 people with COVID-19 and severe disease at seven hospitals in Italy and Spain. The researchers found that people with type O blood were at a lower risk of even being infected with the virus, while people with type A had a higher risk of infection.

The biotechnology company 23andMe—the same one that provides genetic testing an analysis—also shared in a June blog post that preliminary results from its ongoing genetic study of COVID-19 suggested that type O blood "appears to be protective" against the virus. The researchers noted that people with type O blood who participated in their study were up to 18% less likely to test positive for COVID-19 than people with other blood types.

And even before that, preliminary results from a study of more than 2,000 people in China found that those with type O blood had a lower risk of contracting COVID-19. On the flip side, people with type A and type AB had a higher risk of catching the virus. Yet another study of 1,559 people in New York found that those who had type O blood were less likely to test positive for the coronavirus; People with type A blood were 33% more likely to test positive.

What do experts make of this link between blood type and COVID-19 risk?

While it's unclear what's going on with the link between blood type and COVID-19, "there has been ongoing research work to identify the risk factors that increase the risk of COVID infection," Anupama Nehra, MD, an assistant professor at the Rutgers New Jersey Medical School and clinical director of hematology oncology at Rutgers Cancer Institute at University Hospital, tells Health.

There are some theories on why there might be a link: Your red blood cells are covered with molecules that are known as antigens, Thomas Russo, MD, professor and chief of infectious disease at the University at Buffalo, tells Health. These antigens help prompt a response from your body's immune system. It could be that antigens for people with type O blood block the spike protein in SARS-CoV-2, the virus that causes COVID-19, and keeps it from entering into your cells, Dr. Russo says. Blood types can also serve as receptors for viruses and bacteria, and that could be another factor, he says. Or, Dr. Russo says, there may be some other, completely different component of type O blood that works to prevent infection.

But again, experts really don't know what's behind all of this. "We still do not understand all the factors at play," Dr. Nehra says.

It's also important to note that there have been links between blood type and diseases in the past. "People with type O blood may be more susceptible to norovirus," infectious disease expert Amesh A. Adalja, MD, senior scholar at the Johns Hopkins Center for Health Security, tells Health. And people with some blood disorders like sickle cell disease are resistant to malaria, he points out.

But, overall, the link between blood type, genes, and infection risk is a growing area of research, William Schaffner, MD, an infectious disease specialist and professor at the Vanderbilt University School of Medicine, tells Health. "We all recognize that we're not the same, but we have not been able, on a genetic basis, very often, to determine whether certain people with certain genes are more or less susceptible to get an infection if they're exposed to a germ," he says.

What does all of this research around blood type and COVID-19 mean for the average person?

There have been plenty of suggestions thrown around on social media that people with type O blood don't need to stress about COVID-19 as much as everyone else—or that those with type A or AB need to be extra cautious. But experts say that's really not the case.

"There is no real benefit for the individual person," Torben Barington, DMSc, a clinical professor of immunology at the University of Southern Denmark and co-author of the Danish study, tells Health. "All may acquire COVID-19 and all should take the recommended precautions to reduce the risk."

Tom Hemming Karlsen, MD, PhD, head of research at Oslo University Hospital and co-author of the New England Journal of Medicine study, agrees: "I don't see immediate benefits," he tells Health. "As always with findings from so called 'hypothesis-free research,' one first has to understand the reason for the association"—which is something experts are still working on for COVID-19 and blood type.

So while it's tempting to want to run out and get your blood tested, Dr. Karlsen says that's not necessary. "We need to understand the biological mechanisms related to the ABO association first," he says. "Maybe in the end there will be COVID-19 patient subgroups for which it will be important to know the blood type but, for now, I would not recommend testing."

So what happens now, regarding blood type and COVID-19 risk?

Honestly, more research. "At the end of the day, we're still not sure if blood type makes a difference," Dr. Russo says. "As an individual, you have your blood type—there's nothing you can do about it."

Dr. Russo points out that none of the data found that people with type O blood couldn't get COVID-19 or wouldn't have a severe form of the disease: It's just that they seem to be less likely to. "This doesn't mean that you can't get infected, and that's the important message here," he says.

It's also unclear at this point if these findings could do anything in terms of treatment for COVID-19 or a vaccine. "It will be interesting to explore if these blood type antibodies are helpful for preventing infection. That might help better understanding of the disease," Dr. Russo says.

Dr. Karlsen says he hopes his work will help "feed information" to the research community. "Still, more time is needed to tell what this specifically will mean for patients," he says.

As a whole, experts recommend that people—regardless of blood type—keep following guidelines when it comes to preventing the spread of COVID-19. That means practicing social distancing, wearing a mask in public, and washing your hands regular, among other things. And, Dr. Schaffner warns, don't get cocky if you have type O blood. "It's not a suit of armor," he says.

The information in this story is accurate as of press time. However, as the situation surrounding COVID-19 continues to evolve, it's possible that some data have changed since publication. While Health is trying to keep our stories as up-to-date as possible, we also encourage readers to stay informed on news and recommendations for their own communities by using the CDCWHO, and their local public health department as resources.

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