Probability of infection and blood group membership
The so-called secondary attack rate statistically describes the likelihood that a sick person will infect other people in the same household. According to a Nordwegen study, this is around 25% in the case of the omicron variant. This means that in a family of five, an infected family member infects at most one other person in the household, on average.
Secondary attack rate index cases are people in a household who are infected first, i.e. those who bring the infection with them from outside. The secondary infestation rate is defined as the number of non-index household members with a positive test result within 7 days of the index case sampling date divided by the total number of non-index household members.
A team by Rachida Boukhari and Adrien Breiman from the University of Nantes interviewed hospital staff infected with Corona and their partners who live in the same house. They took the blood group and separated the couples in which both partners were infected with the virus at about the same time. In total, they were able to observe in more than 300 couples with more than 600 people how likely they were to transmit the virus depending on blood group affiliation.
Incompatible blood groups: 40% lower risk of infection
In the journal Frontiers in Microbiology, the researchers confirm what British researcher Peter JJ Ellis of the University of Kent had already mathematically modeled in the summer of 2020 in relation to data on the infection process in the first wave of corona: the probability of infecting one partner ran along the blood group transmissibility.
When the blood types were compatible—for example, if the index case had blood type O and the recipient had blood type A, B, or AB—the secondary attack rate was 47.2%. So every second partner was infected. If, on the other hand, it was incompatible, that is, the recipient had blood group 0 and the index case was A, B or AB, then the probability of infection was only 27.9%. The risk of infection was 41% lower if the blood groups did not match.
Blood Group Compatibility There are four main blood groups and the so-called Rhesus factor. People whose blood cells carry antigen A belong to blood group A, those with antigen B to blood group B, those with both antigens to group AB, and those without these antigens to blood group 0. (Positives and negatives indicate the presence or absence of activated Rhesus factor). In principle, blood groups are compatible if their own antigen matches or is not present. Anyone with A+ blood group can transmit their blood to people with A+ and AB+ blood groups. People with blood group 0- can transmit their blood to all other blood groups, people with AB+ only to other people with AB+.
Probably cause antibodies against blood group antigens
According to the study authors, the cause of this very different risk may have to do with antibodies directed against the A and B antigens. “Taken together, our observations may explain why partial protection occurs more often in people with O blood group than than in people with blood groups A and B”. Protection is apparently based on the frequencies of anti-A and anti-B antibodies. “Because blood type A is more common than blood types B and AB, blood type A individuals are less likely to find incompatible infected individuals in a population of Western European descent. blood group O had a lower risk of Covid-19.”
At the same time, the researchers reject a thesis proposed by Shang-Chuen Wu and colleagues. This team suspected that the viruses might be better able to bind to blood group A antigens. In experiments, however, Boukari and Breimann were unable to identify any properties within the blood groups that could explain an infection. A person with blood group 0 has as high a risk of becoming infected with an index case of blood group 0 as all other blood groups.
AB positive: The super recipients of Corona
According to the current model, people with AB+ blood group should have the highest risk of infection of all. This has not yet been noticed in Europe, as this blood group is very rare here. However, researchers from other countries, including India, Pakistan, Saudi Arabia and Iran, have noticed this pattern.
In fact, the French study did not record the severity of the disease. Therefore, it is quite possible that blood group compatibility can also predict the severity of an infection. So incompatible infections would tend to lead to quite mild infections.