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As scientists around the world have raced to understand COVID-19, the general public has been inundated with a flurry of early studies and ensuing recommendations, some of which have been contradictory, leaving us with “coronavirus whiplash.” A recent source of confusion has been the relationship between the coronavirus and blood type. Early in the pandemic, some scientists observed that people with type A blood seemed to be at a higher risk for developing a serious case of COVID-19. However, conflicting research has mounted, and it now looks like the link between the coronavirus and blood type is much weaker than early studies suggested.
Here’s what we know about the coronavirus and blood type.
In the early months of the pandemic, a handful of studies suggested that blood type could be a risk factor for both getting infected with the coronavirus and developing a severe case. In March, a study out of China compared blood samples of 2,173 coronavirus patients with samples from healthy individuals and found that 38 percent of the patients had type A blood, in comparison to 32 percent of the unaffected population in surrounding areas; they also found that those with type O blood appeared to have a reduced risk of getting infected. But in the study itself, researchers cautioned against using their findings to make clinical decisions, and instead urged for “further investigation of the relationship between the ABO blood group and the COVID-19 susceptibility.” (And as MIT Technology Review noted, the study was not peer-reviewed.)
In June, The New England Journal of Medicine published a peer-reviewed study on the subject, in which European researchers looked at more than 1,600 patients who contracted severe cases of COVID-19. (The study characterized serious illness by the need for a ventilator or another form of oxygen supplementation.) Overall, the study found that those with type A blood had a 45 percent higher risk of developing a serious case of COVID-19, while those with type O had a 35 percent reduction in risk.
Last week, the New York Times reported on two newer studies that indicate that blood type may not be as big of a risk factor as earlier research suggested. One study was conducted at Columbia Presbyterian Hospital, which reviewed medical records of 7,770 coronavirus cases. The researchers found that people with type A blood actually appeared less likely to develop a case of COVID-19 serious enough to require ventilation. (Researchers released the initial results from this study, involving 1,559 coronavirus patients, in April; per the Times, the entire study, involving the larger sample size, is still under review for publication in a scientific journal.)
A second study, by Massachusetts General Hospital, showed that blood type did not increase one’s likelihood of falling seriously ill, which researchers defined as requiring intubation or dying. Researchers did, however, find that people with type AB and B blood had a slightly higher risk of testing positive.
Per the Times, both studies found that people with type O had a slightly lower risk of getting the coronavirus. But Anahita Dua, a senior author of Massachusetts General Hospital’s study, cautioned against jumping to conclusions. “These findings need to be further explored to determine if there is something inherent in these blood types that might potentially confer protection or induce risk in individuals,” she told Harvard Medical School.
Public-health experts agree that, no matter what your blood type, no one should assume they’re protected from the coronavirus. “Everybody should practice exactly the same way, whatever your blood type is, in terms of appropriate masking and social distancing,” Dr. Aaron Glatt, chief of infectious diseases at Mount Sinai South Nassau in New York, told NBC News earlier this month. Dua told the Times she “wouldn’t even bring up” blood type when examining why a person might’ve tested positive for the coronavirus. Instead, public-health experts stress that people should place more weight on known risk factors — in particular, older age and underlying health conditions.