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On a day-to-day basis, your blood group doesn’t affect your health. Now, however, studies are looking into the link between blood group and susceptibility to the COVID-19 infection.
Here’s what they have found: People with blood type A seem to be more prone to the new coronavirus infection and more severe illness as a result of COVID-19, whereas people with blood group O are less susceptible to it than every other blood type. There are three studies that support this currently.
Study 1 was done by researchers associated with the COVID-19 Host Genetics Initiative—a group of geneticists from all over the world—who published a paper to this effect in The New England Journal of Medicine on 17 June 2020. In a controlled study, these scientists looked at data from 1,980 patients admitted in hospitals across Spain and Italy and found that “in this cohort, a blood-group–specific analysis showed a higher risk in blood group A than in other blood groups... and a protective effect in blood group O as compared with other blood groups”.
While their findings clearly pointed to a link between blood type and incidence/severity of COVID-19 in the group under scrutiny, the reasons for it are less clear. To be sure, these are early days in genes-led research on COVID-19. And the scientists had started with a simple question: COVID-19 seems to affect different people differently, so could this have something to do with their genetic makeup?
Of course, these scientists aren’t the only ones—or even the first ones—to ponder the connection between blood type and the risk of COVID-19.
Earlier this month, 23and Me, a private company that does genetics testing for customers, also published early findings from ongoing research. Looking at 7.5 lakh people, the American company said they found that “individuals with O blood type are between 9-18% less likely than individuals with other blood types to have tested positive for COVID-19”. In populations where the exposure to COVID-19 coronavirus SARS-CoV-2 was higher, people with O blood type were 13-26% less likely to test positive than people with other blood groups. The people at 23andMe did not, however, find any difference in infection rate or severity among the other blood groups.
It is important to remember that the 23andMe data is part of ongoing research—the company is still recruiting participants and the data has not been pressure-tested by scientists and the medical community.
A third study—pre-print, and not yet peer-reviewed—took data from over 2,000 patients across three hospitals in Wuhan (where the new viral infection first spread in 2019). The researchers found that people with A blood group had “higher risk for acquiring COVID-19 compared with non-A blood groups, whereas blood group O was associated with a lower risk for the infection compared with non-O blood groups”. The researchers also pointed out that these are early days in this research, and these findings should not be used to make clinical recommendations.
While the three studies said different things about blood group A, all three concurred that there is a lower prevalence of COVID-19 among people with O type blood. That said, the reasons for this are less clear.
Doctors have tried to unpack why this could be. One theory is that people with O type blood have 25% less von Willebrand factor in their blood, so they are less susceptible to blood clots than everyone else. Research has shown blood clots in the lungs of severely ill COVID-19 patients.
The second theory has to do with a key difference between the A, B, and O blood types: everyone with blood group A has A antigens (proteins) and B antibodies (proteins to fight B antigens). People with B blood type have B antigens and A antibodies. People with O blood type have no corresponding antigens but antibodies for both A and B.
It has been proposed that when cough droplets from a COVID-19 patient travel in an enclosed space, they carry blood type antigens from the patient's body along with the virus. So, when someone with blood group A or B coughs or sneezes near someone with blood group O, then the immune system in the person with blood group O would become alert and ready to fight the A or B antigens—the conjecture is that when the immune system is awakened to fight A or B proteins, it is also able to mount an early and more effective challenge to SARS-CoV-2.
As of now, though, these theories are just conjecture. A lot more research needs to be done to really unpack the genetic factors (blood type included) that affect the hugely different outcomes (from no symptoms to multiorgan failure) of COVID-19 in patients.
