Europe is currently experiencing a seventh wave of COVID-19, which is largely explained by the immune escape of the new variants, i.e. a strong capacity to resist the protections induced by vaccination and previous ones. infections.
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Erosion of immunity over time
Europe plunged again, at the start of the summer, into a seventh wave marked, almost everywhere, by a rebound in contamination.
In question, a relaxation of the rear gestures, but also, a drop in our immunity.
We now know that the protection conferred by vaccines and by previous infections is eroded after a few months.
“People who contracted an infection with Omicron BA.1 in December are less well protected than they were at the start of the year”, summarizes to AFP Samuel Alizon, research director at the French research center CNRS . “The same goes for the immunity conferred by vaccines: even if it remains very robust against severe forms, it decreases a little against less severe infections”.
BA.4 and BA.5 in ambush
But this new wave is also explained, according to scientists, by the progression of new sub-variants of Omicron, BA.4 and especially BA.5.
In France, according to the latest Public Health France bulletin, a gradual replacement of BA.2 has been observed for several weeks with an increase in the detection of BA.5 (41%) and BA.4 (6%) the week of 13 to June 19.
These sub-variants spread all the more rapidly as they seem to benefit from a double advantage of contagiousness and immune escape, that is to say a strong capacity to escape the immune response.
This was already the case for the Omicron BA.1 sub-variant which was much more capable than Delta of infecting vaccinated or already infected hosts.
Reinfections
It was long thought that an infection served as protection, at least for a while.
But with the Omicron family, it seems that this is not the case, underlines a study from Imperial College published in mid-June in Science.
Scientists analyzed blood samples from more than 700 healthcare workers in the UK. All had received three doses of the Covid-19 vaccine and had been infected with the historical strain or variants.
Their results highlighted that people previously infected with Omicron had a good immune response against the initial strain of the coronavirus and its first variants, but weak against Omicron itself.
It was thought that the Omicron infection could almost "be beneficial, like a kind of" natural reminder "", indicated to AFP Rosemary Boyton, co-author of the study. “What we have found is that it stimulates immunity against itself poorly, or not at all in some cases. This, together with the immune decline after vaccination, may explain the massive increase we are seeing again in infections, with many people being re-infected at short intervals.”
Raise the level of protection
“We are faced with highly contagious variants, which are a bit like stealth agents passing below the radars of immune defenses; it is a real complexity of the Omicron band”, underlined last week Gilles Pialoux, head of service at the Tenon hospital, in Paris.
These "very contagious" variants require that we increase the level of protection for the most fragile," he added.
Because, and this is good news, vaccines remain effective against serious forms of the disease.
For most European countries, the top priority is that the elderly and immunocompromised receive a second booster dose.
“Currently, the level of immunity of the population is good, but not perfect”, underlined Sunday Alain Fischer, president of the council of orientation of the French vaccine strategy. “This is why a second booster should be recommended for people over 60 and for fragile people, whose immune system and memory are less robust”.
