Europe is currently experiencing a seventh wave of COVID-19, which is largely explained by the new variants’ immune escape, i.e. a strong ability to withstand the protection provided by vaccination and previous infections.
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Erosion of immunity over time
Europe plunged again into a seventh wave earlier in the summer, marked by a surge in contamination almost everywhere.
In question, a relaxation of rear gestures, but also a drop in our immunity.
We now know that the protection offered by vaccination and previous infections wears off after a few months.
“People who contracted Omicron BA.1 in December are less well protected than at the beginning of the year,” Samuel Alizon, head of research at the French research center CNRS, told AFP. “The same applies to the immunity conferred by vaccines: even if it remains very robust against severe forms, it weakens somewhat against less severe infections.”
BA.4 and BA.5 in ambush
But this new wave, according to scientists, is also explained by the progression of new subvariants 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 the detection of BA.5 (41%) and BA.4 (6%) increasing in week 13 to 19 June.
These subvariants spread all the faster as they seem to benefit from a dual advantage of contagiousness and immune evasion, ie a strong ability to evade the immune response.
This was already the case with the subvariant Omicron BA.1, which was much better able than Delta to infect vaccinated or already infected hosts.
For a long time it was thought that an infection at least temporarily serves as protection.
However, this does not appear to be the case with the Omicron family, according to a study by Imperial College published in Science in mid-June.
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 showed that people previously infected with Omicron had a good immune response against the original strain of coronavirus and its early variants, but weak against Omicron itself.
It was thought that the Omicron infection could be downright “beneficial, like a kind of ‘natural memory’,” Rosemary Boyton, co-author of the study, told AFP. “What we found is that it stimulates immunity against itself poorly, or in some cases not at all. This, together with the decline in the immune system after vaccination, could explain the renewed massive increase in infections, with many people becoming reinfected at short intervals.”
Increase the level of protection
“We’re faced with highly contagious variants that are a bit like stealth agents that go under the immune system’s radar; it is a real complexity of the Omicron band,” underlined Gilles Pialoux, service manager at the Tenon Hospital in Paris, last week.
These “very contagious” variants require that we increase the level of protection for the most vulnerable,” he added.
Because, and this is good news, vaccines remain effective against severe forms of the disease.
For most European countries, getting a second booster shot is a top priority for the elderly and immunocompromised.
“Currently, the level of immunity in the population is good, but not perfect,” stressed Sunday Alain Fischer, President of the French Vaccination Strategy Orientation Council. “Therefore, a second booster should be recommended for those over 60 and for frail individuals whose immune systems and memory are less robust.”