According to two studies released recently, people with blood type O may be less vulnerable to COVID-19 and have a decreased chance of becoming seriously ill. Experts add that there is a need for further research.
The study provides further proof that the blood group (also known as the blood type) can play a role in the susceptibility of a person to infection and their chance of having a severe case of the disease. The reasons for this relation are not clear and further research is needed to establish what consequences it has for patients, if any.
Study from Denmark
The study, conducted in Denmark, found that only 38.4 percent of the 7,422 people who tested positive for COVID-19 were blood type O, while that blood type made up 41.7 percent of the total population.
By comparison, 44.4% of group A tested positive, while the blood type accounts for 42.4% in the larger Danish population.
Study from Canada
In another study, researchers in Canada found that among 95 patients critically ill with COVID-19 a higher proportion (84%) of blood type A or AB required mechanical assistance in breathing compared with patients with blood group O or B, which was 61 percent.
The Canadian study also showed that those with type A or AB blood had a longer stay in the intensive care unit, a medium of 13.5 days , compared to those with O or B blood group who spent an average of nine days in the ICU.
“As a clinician it is at the back of my mind when I look at patients and stratify them. But in terms of a definitive marker we need repeated findings across many jurisdictions that show the same thing,” said Dr. Mypinder Sekhon, one of the authors of the Canadian study.
“I don’t think this supersedes other risk factors of severity like age and co-morbities and so forth,” added Mr. Sekhon. “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.”
Why could it be?
Although there are many hypotheses, scientists do not yet know what mechanism might explain the association between different blood groups and COVID-19.
Sekhon said it could be described by people with type O blood having less of a main clotting factor that makes them less susceptible to blood coagulation issues. Clotting has been an important driver of COVID-19’s severity.
Other potential theories include antigens in the blood group and how they affect the production of antibodies that combat infection. Or it may be related to genes associated with blood types and their effects on immune system receptors.
“It’s a repeated, interesting scientific observation that really warrants further mechanistic work,” he said.
Don’t be concerned
The majority of humans fall into one of four classes of blood: A, B , AB or O. If you have to have a blood transfusion, it makes very little difference to most people’s everyday lives. Dr. Torben Barington, senior author of the Danish paper said that people should not worry unduly about the association between the blood type and COVID-19.
“We do not know whether this is some kind of protection of group O, or whether it’s some kind of vulnerability in the other blood groups,” he said. “I think this has scientific interest, and when we find out what the mechanism is, perhaps we’re able to use that proactively in some way in regard to treatment.”
In the Danish study, researchers analyzed data on Danish individuals who were tested between 27 February and 30 July and compared the distribution of blood types among those individuals to data from individuals who were not tested. They found that the risk factor for hospitalization or death from COVID-19 was not the blood group.
Need for more research
Dr. Amesh Adalja, senior scholar at a US university, who was not involved in any of the studies, said the results of the two new studies provide “more convergent evidence that blood type can play a role in a person’s susceptibility to COVID infection and their risk of getting a serious bout of COVID-19.”
In a separate study published in The New England Journal of Medicine in June, evidence was found that in some COVID-19 patients and healthy individuals with type A blood had a higher risk of being infected and those with type O blood had a lower risk. The previous genetic research, combined with the two recent studies is “suggestive that this is a real phenomenon that we are seeing,” says Adalja, whose work focuses on emerging infectious diseases.
“While we’re not quite to the point where this is ironclad, it’s clearly suggestive, and we have not seen anything inconsistent with this. The same pattern has been emerging with O blood type tending to be the one that’s standing out,” Adalja said.
Adalja said that in the medical literature, blood types and their susceptibility to different infections have been studied widely. For instance research shows that individuals with blood type O tend to be more vulnerable to infection from norovirus (causes vomiting and diarrhea).
As for the novel coronavirus that causes COVID-19, “We need to figure out the mechanism and understand it at the molecular level to be able to say for sure how this is occurring, that this is really the O blood type and not something that kind of tracks with O blood type,” Adalja said.
“We’re starting to see enough now that I think it’s an important research question to answer,” he said. “There’s more science to be done here, but it seems to me that there’s more evidence accumulating for this hypothesis.”
