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Experts say past studies have shown a connection between blood types and certain conditions and illnesses. Getty Images
  • In a new study, researchers report that people with type O blood appear to be at lower risk for contracting the novel coronavirus that causes COVID-19.
  • In a June study, researchers concluded that people with type A blood have a higher risk of contracting the novel coronavirus.
  • In March, a study from China concluded that people with type A blood may have a higher risk of contracting the new coronavirus than people with type O.
  • The experts add that past research has shown some connection between blood type and illnesses such as the stomach flu, as well as the risk of stroke and cognitive impairment.

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A new study indicates that people with type O blood have a lower risk of contracting the novel coronavirus that causes COVID-19 than people with other blood types.

The researchers also noted that people with type O blood are less likely to develop a serious illness if they do have the virus.

The findings are similar to a study published in June where researchers concluded that people with type A blood were associated with having a 45 percent higher risk of contracting the novel coronavirus.

Those researchers studied 1,900 people in Spain and Italy who were seriously ill with COVID-19 and compared their results with 2,000 people who were not sick.

In March, a study out of China suggested that people with type A blood might be more susceptible to getting the virus and people with type O blood might have more protection against the virus.

The reports have some experts worried that people with type A blood might panic or worry and that people with type O blood might let their guard down or get too complacent.

“These results can’t be used to lessen the serious precautions that everyone needs to take, regardless of their blood type,” Dr. Mary Cushman, MSc, a hematologist and professor at the Larner College of Medicine at the University of Vermont, said in March.

“Someone on social media this weekend wondered if the type O people in families should be the ones sent out for shopping, for instance,” Cushman told Healthline. “We definitely don’t want people thinking they can be protected and don’t have to take precautions because they are type O.”

The March study came out of Wuhan, China, where the first known cases of COVID-19 were discovered.

In the study, scientists looked at the blood types of 2,173 people who had been diagnosed with COVID-19 and compared that with the blood types of the general population in that region.

They found that in the normal population, type A was 31 percent, type B was 24 percent, type AB was 9 percent, and type O was 34 percent.

In those with the virus, type A was 38 percent, type B was 26 percent, type AB was 10 percent, and type O was 25 percent.

The researchers concluded that “blood group A had a significantly higher risk for COVID-19 compared with non-A blood groups. Whereas blood group O had a significantly lower risk for the infectious disease compared with non-A blood groups.”

The CDC recommends that all people wear cloth face masks in public places where it’s difficult to maintain a 6-foot distance from others. This will help slow the spread of the virus from people without symptoms or people who do not know they have contracted the virus. Cloth face masks should be worn while continuing to practice physical distancing. Instructions for making masks at home can be found here.
Note: It’s critical to reserve surgical masks and N95 respirators for healthcare workers.

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Experts expressed concerns after the recent study that people with blood types other than type A might “let their guard down.”

Similar sentiments were expressed after the March study.

“This is an interesting study,” said Patricia Foster, PhD, a microbiologist and professor emerita of biology at Indiana University, told Healthline in March. “But it needs verification. If they can come up with more solid numbers and bigger studies, it’s something to look out for.”

“It still requires full peer review, but it looks like the methods were generally appropriate,” Cushman said. “They interpret specific findings for certain blood groups, but I think the essence of what they observed is that people with O blood group have a lower risk of infection than all the other blood groups.”

“It’s very compelling and the results are not entirely surprising since we know blood group is important in other settings and other viruses,” she added.

Experts say research shows many diseases have been linked to blood types.

“We found that type AB is related to stroke risk and in general, to cognitive impairment risk. Although not all studies have observed that,” Cushman said.

“Type O, compared to other types, also protects against heart attacks and blood clots in the veins, known as venous thrombosis,” she added.

“We don’t know the mechanisms yet, but we know there are differences by blood type in certain clotting factors and factors in the circulation that relate to blood vessel lining cell connections,” Cushman said.

Dr. Foster has looked at the connection between intestinal illnesses such as norovirus and blood types.

“Norovirus has a clear biological reason why blood type would make a difference,” she said. “The norovirus actually uses the sugars on the cell surface to attach itself to the cell.”

In general, people who don’t make the H1-antigen and those with B type blood will tend to be resistant, whereas people with A, AB, or O blood types will tend to get sick.

“At the end of the day, we won’t know what to do about this information to prevent or treat infection,” Cushman said. “For example, I wouldn’t ease precautions for healthcare workers who are type O. This finding does not mean they are immune.”

“Everyone needs to continue washing their hands, keeping a physical distance from others, and following all the things public health experts are recommending,” she said.