COVID-19 and blood type: what to know about doctors

We are all painfully aware of the many unanswered questions about COVID-19. The relatively new disease caused by the new coronavirus has yet to be cured, and efforts to contain it have so far been difficult as states continue to reopen and people tire of social estrangement. One of the most important questions that haunt the experts is why otherwise healthy young people really got sick and died from COVID-19, while others had hardly any symptoms.

Researchers are studying a number of theories, including genetic mutations that can put people at higher risk for severe infection, and whether the viral load or the amount of virus a person is exposed to plays a role in the severity of symptoms of a person. But a series of new studies point to another factor that could affect a person’s experience with the coronavirus: their blood type.

While these studies are a scientifically important starting point, “it is too early to use this information to apply the risk of COVID-19 to a specific person based on their blood group,” says Eric A. Gehrie, MD, assistant professor of pathology and surgery and the co-director of the patient blood management program at Johns Hopkins Hospital in Baltimore, Maryland.

First of all: what are blood types and how do they work?

Your blood plays an important role in the ability of your immune system to defend the body. The white blood cells circulating in the bloodstream produce antibodies to attack foreign invaders like germs and viruses. And compounds on the surface of red blood cells called blood group antigens help recognize these foreign invaders.

Your blood type is determined by the presence (or absence) of those A or B antigens on the surface of your red blood cells, which varies by your blood type, says Raymond Comenzo, MD, hematologist and director of transfusion services at Tufts. Medical Center. The vast majority of people are divided into one of the four main blood types: A, B, O, or AB. The most common is group O, and the least common is group AB. People in group A have A antigens, group B has B antigens, group O does not have A or B antigens, and AB has A and B antigens.

Your cells also make antibodies A or B against blood type antigens that do not do it to have. People with group A blood produce anti-B antibodies and people with group B blood produce anti-A antibodies. People with group O blood produce anti-A and anti-B antibodies, while people in group AB do not produce anti-A or anti-B antibodies. If your cells come into contact with cells with a different set of antigens than you already have, your antibodies attack the cells, which are considered invaders.

What do blood types have to do with COVID-19?

Several recent studies suggest a link between blood type and susceptibility to SARS-CoV-2, the virus that causes COVID-19. The studies, however, “don’t even begin to address the mechanistic side of how it would work,” says Dr. Gehrie, which means that while there is a potential connection between the two, we don’t know why or how it would work. job.

The most compelling study, published this month in the New England Journal of Medicine, scanned the entire genome of more than 4,000 people in Spain and Italy for genetic differences between those who were diagnosed with COVID-19 and those who were not. They found a weak but significant link to blood type (which is determined by genetics): People with group A blood had a slightly higher risk of COVID-19 infection, while those with blood from group O appeared to be slightly protected against COVID- 19)

Another study in the British Journal of Hematology Group A COVID-19 patients were also found to have an increased risk of hospitalization compared to group O patients. And some other preliminary studies, including an analysis by the genetic testing company 23andMe, have reached similar conclusions. Although these have not been peer reviewed and published in a journal.

“The fact that several different research groups are reporting this association probably speaks to some kind of association. But at present, the strength of this association is highly uncertain, “says Dr. Gehrie.

Why would your blood type potentially affect your risk of COVID-19?

This is not the first time that researchers have made a connection between the blood type and other forms of the coronavirus. A 2005 study after the 2003 outbreak of the SARS-CoV-1 virus (which causes SARS disease) found that people with blood type A had a higher risk of infection with that coronavirus than people with other blood types.

Jacques Le Pendu, PhD, director of research at the University of Nantes in France studying viruses, was intrigued by these findings and came up with a blood group hypothesis to explain them. Their 2008 study manipulated cells in a laboratory setting to show that those that produced anti-A antibodies blocked the binding of the SARS-CoV-1 virus to the receptors in the cells, so the virus was unable to reproduce. “It is not a formal test … but it is a strong indication,” says Dr. Le Pendu.

For a virus to make you sick, it has to bind to the cells in your body where it can reproduce. The viruses that caused the 2003 SARS outbreak (SARS-CoV-1) and the current COVID-19 outbreak (SARS-CoV-2) reproduce in epithelial cells of the upper respiratory tract. Epithelial cells also express A or B antigens, so as a virus reproduces in an infected person, Dr. Le Pendu says that the copies likely contain the same antigens from that person. In a person with type A blood, for example, the virus will have group A antigens. If a person with type B or type O blood is exposed to that sick person with type A blood, they may not get sick, because their antibodies anti-A recognize A antigens and block the virus.

A second theory explains why people with some blood types may be more likely to have severe results from a COVID-19 infection. Having type A or B blood is linked to an increased risk of developing blood clots, and unusual blood clots are a notorious complication of COVID-19. These two concurrent hypotheses could work together. They are not mutually exclusive, ”says Dr. Le Pendu.

Doctors interviewed for this article emphasized that there is no evidence yet for any of these theories, and that you can explain almost anything you want with selected data. It is impossible to know if the link between COVID-19 and blood type is due to genetics or another factor without further investigation.

“The human body is really complex, with all these interacting characteristics,” says Eleanor J. Murray, ScD, an assistant professor of epidemiology at the Boston University School of Public Health who has been studying the COVID-19 outbreak. She notes that certain blood types are more common by race and ethnicity. Since race appears to be a factor in COVID exposure or treatment in the first place, which could better explain these findings.

What does this mean for the way we fight the virus?

All experts agree that more research is needed. “We need to understand the association more specifically to determine if there is valuable knowledge relevant to the development of vaccines or treatments,” says Dr. Comenzo.

Dr. Gehrie says this research can potentially give us a better understanding of how the virus infects people and causes symptoms, which could help scientists develop preventive measures and treatments based on a person’s individual risk. “For now, the strength of the association is unknown,” he says.

“The real question is how important [blood type] it is in terms of risk or protection against infection or disease … The truth will only be known when we understand how it really works, “says Dr. Le Pendu. His team is working on a document they hope to present for peer review in the coming weeks, which he says scientifically demonstrates his 2008 hypothesis.

If his theory works, it could work as “an imperfect natural vaccine …[but] it’s not true protection as a good vaccine would provide, “he says. If the blood group could offer any protection against the disease, it could ultimately delay the spread of the virus at the population level. And less spread would mean less chance of get sick, even if you have type A or B blood.

One catch is that people have varying levels of antibodies, and many of us have levels so low that they would not protect us from the virus. But Dr. Le Pendu is hopeful that researchers can find a way to increase antibody levels to increase protection. If you receive a blood transfusion with an incompatible blood type, that is, you have type A blood and receive type B blood, it stimulates the body to massively pump antibodies that can cause serious problems such as kidney failure. However, this also suggests that it is possible to increase antibody levels; experts would have to figure out how to do it safely and cheaply at scale. “We have nothing that works so far. We are beginning to see how that [could] let it be done, “says Dr. Le Pendu.

What are the conclusions for ordinary people?

Even if the blood group theory works, you can still get sick regardless of your blood type. If you are type O, for example, you can get sick if you are infected by another type O person. “Your overall risk [would be] a little lower, but that doesn’t mean you’re protected, “says Dr. Le Pendu.” It slows down virus transmission overall, but at the individual level it still carries almost the same risk as everyone else. “

Bottom Line: Anyone from any blood group can become seriously ill from COVID-19. Until we have a vaccine or a cure, it is essential to continue to follow current guidelines on wearing a mask, washing your hands frequently, and practicing social distancing. “The blood type is almost irrelevant,” says Dr. Comenzo.

The good news is that the best researchers in the world are working on the problem. “The number of trials for treatments is exploding,” says Dr. Murray. Hopefully we’ll have better treatments, and maybe even a full shot, soon.