“Do you think we are going to have a medal, the last French people who have never had Covid-19? “It’s crazy that having spent a week locked up taking care of my son, I didn’t catch him”…
Olivier Véran explained Wednesday evening on BFM-TV that one in two French people “at least” had been affected by Covid-19 since the start of the pandemic. Why did some get sick three times… and others zero?
Two years after the arrival in our lives of the coronavirus, there are still many mysteries. Among the hypotheses, one track intrigues a lot and is explored by French researchers: that of the blood group. Are French people with blood group O really more protected? And why ? 20 Minutes make the point.
What do the studies say?
Many studies have addressed this question. including a British one, published in the scientific journal Epidemics in June 2021, which concluded that blood type had an impact on the risk of transmission.
If all the studies do not all point in the same direction, we can remember that “there is a small link, not considerable, between blood group and infection with Sars-Cov-2, summarizes Jacques Le Pendu,
research director at Inserm in Nantes in immunology. There is a small difference, well documented, via a body of studies and a meta-analysis [une méthode scientifique combinant les résultats d’une série d’études indépendantes sur une même question] showing that people in group 0 would have a reduced risk of 20% compared to other citizens and those in group A an increased risk of about 20%. »
How to explain it?
To be able to follow, you must have two important pieces of information in mind. The first is that blood groups are unevenly distributed in France. Basically, the groups A (44%) and O (42%) are the most common, B (10%) and AB (4%) much rarer. “As a result, the data is less solid,” explains Jacques Le Pendu. Second basic data: the blood group tells us about the antibodies that this person produces. A French person who belongs to group A has anti-B antibodies, that of group B has anti-A antibodies, on the other hand that of group O has anti-A and anti-B antibodies. This is why a person with group O can donate blood to both group A and group B, but can only receive blood from group O.
Jacques Le Pendu’s team wondered if the logic of blood transfusion could apply to Covid-19 infection. “Because the virus carries the blood group of the person”, specifies the immunologist.
How to verify this intuition? “We looked at what happens in a couple, infected and symptomatic, who share the same room, therefore for whom the risk of being infected is maximum, he explains. We asked not only their blood group but in which way the virus is transmitted. What the study concludes is that in cases of incompatibility between the two spouses, the risk of the partner catching symptomatic Covid-19 is reduced by half. “Basically, if your partner cannot give you blood, you are less likely to catch Covid if he is positive. This observational study was published on January 5, 2022 in Frontiers in Microbiology.
Very relative protection
Does this mean that when you belong to blood group O, there is no need to respect restrictions and barrier gestures? Far from there. For four reasons. First of all, the blood group is only one data among others which provides information on the health of an individual and we are talking about partial protection. If a 75-year-old person (we know that old age is the first comorbidity for Covid-19), diabetic, very exposed to the virus, belongs to group O, he still has immense risks of catching the virus. !
Second limit: “everyone is at risk anyway, it’s just a question of probability, insists Jacques Le Pendu. For example, if you are A, you are only partially protected if the donor is B or AB. However, only 10% of French people are B or AB, so you are in a situation of incompatibility with 10% people met. For the O, on the other hand, it is in 58% of the cases. So everyone can benefit from this protective effect, but this probability is higher for Os than for As.
Third obstacle: this protective effect has been confirmed within a couple. “On a more global scale, the effect is diluted because you will have other people of the same compatible blood group, nuances the researcher. In a party with thirty people, for example, there is a good chance that you will come across someone who has the same blood type as you! »
Finally, and this is a major detail, all the studies on this question date from before the arrival of the Delta and Omicron variant. “On this last variant, we have no data, recognizes the immunologist. I will not be surprised if faced with such a contagious virus, this protection disappears. »
An effect also on the severity of the disease?
So much for the infection part. But are people in group O, if they catch Covid-19, less likely to die from it? “There are some data that go in this direction, but it is only seen in patients who are at a very serious stage”, answers Jacques Le Pendu. Basically, in patients on sheaves, there is a protective effect for the O. “Which is only partial once again! If you are O, you still risk being hospitalized and going to the sheave. But you have a better chance of getting out of it… and a little faster. »
Why ? “It is due to a completely different phenomenon, known for a long time and visible in other diseases. Group O people are less prone to thrombosis and coagulation defects. “However, when the condition of a Covid patient deteriorates, the immune system can overreact, damage blood circulation and lead to death. A good reason to fetch your lost blood group card in the depths of a file?