A man receives a dose of vaccine against the Covid-19 coronavirus in a social center in the popular district of La Gavotte Peyret, in Septeme-Les-Vallons (Bouches-du-Rhône), on January 12, 2022. CLEMENT MAHOUDEAU / AFP The variant Omicron, decidedly, is a UFO. This avatar of the SARS-CoV-2 virus, whose global influence has become almost hegemonic, is well known for differing from its predecessors by its numerous mutations. When it was detected in South Africa in November 2021, in its BA.1 version (the one that swept across Europe in December), it was already carrying about fifty, compared to the historic Wuhan strain. Since then, its successive later versions have acquired new ones, in particular BA.2, and now BA.4 and BA.5. However, the latter “will be ultra-majority in about three weeks in France”, according to Mahmoud Zureik, professor of epidemiology and public health at the University of Versailles-Saint-Quentin (Yvelines). Read also Article reserved for our Covid-19 subscribers: BA.2, the Omicron sub-variant whose features are gradually taking shape Researchers are gradually discovering how, thanks to these mutations, Omicron escapes our immune defences. “Omicron is clearly a variant apart. On the genealogical tree of the SARS-CoV-2 virus, it comes from a branch distant from those of the other variants, recalls Professor Olivier Schwartz, head of the virus and immunity unit at the Institut Pasteur in Paris. For example, it is not detected at all by the antibodies of doubly vaccinated people who have not received a third dose. And very poorly detected by the antibodies of those who have been infected with the Wuhan strain. Conversely, in in vitro studies, the antibodies of people infected with Omicron recognize very little of the above variants. Can people infected with BA.1 be infected with the latest versions of Omicron, such as BA.5? Three recent studies shed light on this question. A South African study, unreviewed by peers and published on April 24, suggests that antibodies from unvaccinated people infected with BA.1 neutralize BA.4 and BA.5 about 7.5 times less well. Clearly, a person infected with Omicron at the beginning of the year is not completely protected against the risk of reinfection with BA.4 or BA.5, especially if they are not vaccinated. Different sub-variants However, are reinfections with BA.4 or BA.5 more frequent than with BA.1? Not sure. “About 15% of the BA.4 and BA.5 cases investigated reported a previous infection with SARS-CoV-2”, writes Public Health France, on June 17, in its risk analysis on the variants. This corresponds to “a rate of reinfection similar to the cases of BA.1” noted by the agency. Read also Article reserved for our Covid-19 subscribers: with the Omicron variant, increasingly frequent reinfections Another study, published in the journal Nature on June 17, looked at the antibodies produced after an infection with BA.1 , in people triple vaccinated with Coronavac (a Chinese inactivated virus vaccine). Results: these antibodies neutralize more and more badly the various sub-variants of Omicron, as they follow one another. “This study therefore raises the question of the relevance of vaccines under development that target only the BA.1 sub-variant of Omicron,” said Mahmoud Zureik. You have 51.96% of this article left to read. The following is for subscribers only.
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