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immunity, blood type…why some people don’t get it?

Despite well-respected barrier gestures, some people have been infected with covid-19. Others, conversely, seem to have never contracted the disease, even being contact cases on several occasions. How to explain it?


One of the hypotheses that can be put forward to explain that some of us pass “between the drops” would be that of a discreet contamination. Some develop asymptomatic forms. Without an antigen test or PCR, these people do not realize that they are carriers of the virus. Thus, the latter think they have never contracted covid-19, when in reality they have had it in a form with no or very few symptoms.

On the other hand, the purpose of the vaccine is to prevent serious forms of the disease and to reduce contamination. Vaccinated people therefore have less risk of developing symptomatic forms of the disease, and therefore their contamination can sometimes go unnoticed.


We are not all equal when it comes to immunity. An infection with the virus or a vaccination allow patients to develop, among other things, neutralizing antibodies to defend themselves in the event of new contact with the disease. Some individuals produce a large amount of antibodies, and over the long term. Others, on the contrary, produce little, and their number drops rapidly. This is why some people are infected despite vaccination, or are reinfected after a first contamination.

It is important to remember that the vaccine does not provide the same protection to everyone. The serum will be more or less effective depending on the patient. The variability of immunity from one person to another can be explained by the great genetic diversity in humans. This is why the response to infections against a given pathogen is not the same from person to person!

>> Read also: Everything you need to know about how immunity works


Recently, a study by researchers at Imperial College London showed that immune T cells developed following infection with other human coronaviruses such as the common cold may play a protective role.

The study involved 52 individuals who lived with someone infected with SARS-CoV-2. The 52 volunteers were tested by PCR on D+4 and D+7. Samples of their blood were collected within a week of their exposure to the virus in their household. The researchers found that the 26 people who did not contract covid had a much higher level of T cells, compared to those who were infected by the member of their household.

These lymphocytes recognize SARS-CoV-2 and target its internal proteins rather than the virus’ spike protein to protect themselves from infection. In the 26 uncontaminated individuals, these T cells were created following a previous infection, due to a cold of the family of coronaviruses. These pre-existing cells would therefore have protected them from covid contamination, according to the researchers. It should be noted, however, that the participants in this study being very few in number, the data must be supplemented with a larger cohort.

In addition, the researchers insist on this point: having contracted a cold does not offer complete protection against covid, and recall that the best way to protect yourself from the disease remains vaccination with a booster dose.


This is a surprising and yet not new singularity: already, in 2005, the team of Jacques Le Pendu, director of research at the Nantes-Angers oncology and immunology laboratory, had looked into this link between blood group and immunity, following the SARS epidemic.

Since then, a Chinese study published in 2020 has shown that people with blood group O are less likely to be infected with covid than people from another group.

A new study, published in June 2021, went even further: it suggests that blood group compatibility could promote contamination. Thus, there would be more risk of being infected by a person of the same blood group as his.

Immunity, blood group, vaccination… are all ways to explain the non-contamination of certain individuals. But they remain leads: they are not exhaustive, and do not take into account potential known factors (the environment for example), or even unknown ones.

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