A growing body of research suggests a link between blood type and coronavirus risk.
New studies have found that people with Type O blood have a lower risk of getting the coronavirus and are less likely to get severely sick if they do get infected.
Some research has also found that COVID-19 patients with Type O or B blood spent less time in the ICU and were less likely to need a ventilator.
But blood type shouldn't be used to judge an individual patient's risk.
Research is coalescing around the idea that people with Type O blood may have a slight advantage during this pandemic.
One of the new studies specifically found that COVID-19 patients with Type O or B blood spent less time in an intensive-care unit than their counterparts with Type A or AB. They were also less likely to require ventilation and less likely to experience kidney failure.
These new findings echo similar findings about Type O blood seen in previous research, creating a clearer picture of one particular coronavirus risk factor.
Patients with Type O or B blood had less severe COVID-19
Both new studies came out Wednesday in the journal Blood Advances. One looked at 95 critically ill COVID-19 patients at hospitals in Vancouver, Canada, between February and April.
They found that patients with Type O or B blood spent, on average, 4.5 fewer days in the intensive-care unit than those with Type A or AB blood. The latter group stayed, on average, 13.5 days in the ICU. The researchers did not see any link between blood type and the length of each patient's total hospital stay, however.
They did, however, find that only 61% of the patients with Type O or B blood required a ventilator, compared to 84% of patients with Type A or AB.
Patients with Type A or AB, meanwhile, were also more likely to need dialysis, a procedure that helps the kidneys filter toxins from the blood.
"Patients in these two blood groups may have an increased risk of organ dysfunction or failure due to COVID-19 than people with blood types O or B," the study authors concluded.
A June study found a similar link: Patients in Italy and Spain with Type O blood had a 50% reduced risk of severe coronavirus infection (meaning they needed intubation or supplemental oxygen) compared to patients with other blood types.
People with Type O blood had 'reduced susceptibility' to infection
The second new study found that people with Type O blood may be at a lower risk of getting the coronavirus in the first place relative to people with other blood types.
The team examined nearly half a million people in Denmark who were tested for COVID-19 between late February and late July. Of the roughly 4,600 people who tested positive and reported their blood type, 38.4% had Type O blood.
That's lower than the prevalence of Type O in a population of 2.2 million Danish people, 41.7%, so the researchers determined that people with Type O blood had disproportionately avoided infection.
"Blood group O is significantly associated with reduced susceptibility," the authors wrote.
Other studies found a similar link between blood type and COVID-19 risk
In general, your blood type depends on the presence or absence of proteins called A and B antigens on the surface of red blood cells — a genetic trait inherited from your parents. People with O blood have neither antigen. It's the most common blood type: About 48% of Americans have Type O blood, according to the Oklahoma Blood Institute.
The new studies about blood type and coronavirus risk align with prior research on the topic. A study published in July found that people with Type O were less likely to test positive for COVID-19 than those with other blood types. An April study, too, (though it has yet to be peer-reviewed) found that among 1,559 coronavirus patients in New York City, a lower proportion than would be expected had Type O blood.
And in March, a study of more than 2,100 coronavirus patients in the Chinese cities of Wuhan and Shenzhen also found that people with Type O blood had a lower risk of infection.
Past research has also suggested that people with Type O blood were less susceptible to SARS, which shares 80% of its genetic code with the new coronavirus. A 2005 study in Hong Kong found that most individuals infected with SARS had non-O blood types.
Despite this growing body of evidence, however, Mypinder Sekhon, a co-author of the Vancouver study, said the link is still tenuous.
"I don't think this supersedes other risk factors of severity like age and comorbidities and so forth," he told CNN, adding, "if one is blood group A, you don't need to start panicking. And if you're blood group O, you're not free to go to the pubs and bars."
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