Blood type may predict your COVID-19 risk, study shows

A new study published in Blood Advances this week suggests that individuals with Type O blood may be less likely to contract COVID-19 and less likely to experience severe outcomes if they do. The researchers used health registry data from Denmark to analyze the blood types of 473,000 individuals who tested positive for COVID-19 and compared it to the 2.2 million people in the overall population.

A surgical-gloved hand holds a red-topped glass vial that appears to be filled with blood.
A new study suggests that people with Type O blood are less likely to get COVID-19 and less likely to get severely ill if they do contract it. (Photo: Getty Images)

Their results suggest that those with Type A, B or AB blood may be at increased risk of contracting the virus and that those with Type A or AB blood may be more likely to become severely ill and need mechanical ventilation. The results imply that those with Type O blood may have some protection against COVID-19 and the potential outcomes with severe illness, including organ damage.

“The unique part of our study is our focus on the severity effect of blood type on COVID-19. We observed this lung and kidney damage, and in future studies, we will want to tease out the effect of blood group and COVID-19 on other vital organs,” one of the study’s authors, Dr. Mypinder S. Sekhon from the University of British Columbia told Science Daily. “Of particular importance as we continue to traverse the pandemic, we now have a wide range of survivors who are exiting the acute part of COVID-19, but we need to explore mechanisms by which to risk stratify those with longer-term effects.”

The study isn’t the only one to suggest that blood type may be an indicator of how individuals with COVID-19 will fare — and how likely they are to get it in the first place. A study from the New England Journal of Medicine in June concluded that Type O blood may be associated with a lower risk of contracting COVID-19 and that those with Type A may be more likely to contract it. The authors also mentioned a 2005 study from the Journal of the American Medical Association, which showed a similar connection between Type O blood and the original SARS virus.

Dr. Amesh Adalja, a senior scholar at Johns Hopkins University Center for Health Security, says blood type has been identified as a factor in other illnesses. “We’ve seen in the past — for example, having certain blood types has some influence on norovirus susceptibility,” he says. “But with COVID-19 it seems to be that there are several lines of converging evidence pointing to blood type playing some role. It hasn’t quite been unraveled completely yet, but it looks to me like this is probably a real signal.”

Dr. William Schaffner, an infectious disease expert at Vanderbilt University School of Medicine, agrees. “We know that everyone who gets exposed to an infection doesn’t get sick or gets sick to varying degrees, and we’ve wondered whether there are genetic predispositions to that,” says Schaffner. “Very few of those have been discovered with any frequency... So this is very provocative.”

While it’s too soon to know exactly what about O blood acts as a protective measure, Adalja says it may have something to do with immune response. “Blood type is intricately connected to immune system function,” says Adalja. “That’s exactly why you can only get a blood type from somebody that has the same blood type because there are antibodies.”

Schaffner agrees that may explain it but offers another idea. “Maybe they have a different immune response, or maybe it’s something different on their cells that makes it more difficult for the virus to multiply in their bodies,” says Schaffner. “Type O could be what we call a marker. It might not be the core reason. There might be other genetic aspects that ... are the determining factors. Typo O is just easy to measure.”

Overall, both say the study is mainly of use to science at this point — and shouldn’t be taken as a reason to modify behavior. “It’s more exciting to those of us trying to study how viruses make people sick than it [is] for the general population,” says Schaffner. “What this does not mean is that everybody should go out and get their blood types and the O people can be careless and not wear masks. No, that’s not what this means. This is just a fascinating scientific piece of information that needs further study to understand.”

“It’s not ironclad,” adds Adalja. “It doesn't mean that if you have Type O blood that you can live as if there’s not a pandemic ... It just means that this might be something that helps us explain why some people have severe illness and others people do not.”

For the latest coronavirus news and updates, follow along at According to experts, people over 60 and those who are immunocompromised continue to be the most at risk. If you have questions, please reference the CDC’s and WHO’s resource guides.

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