Does Omicron also escape treatments based on monoclonal antibodies?


With its S protein with 32 mutations, Omicron undermines the effectiveness of vaccines and also that of therapeutic antibodies developed to fight against severe forms of Covid-19. This is the conclusion of a study still in prepublication, published recently.

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Omicron seems to escape to vaccine antibodies, to those present in the serum of convalescent patients infected with another variant and also to monoclonal antibodies used as drugs. This is what an experiment shows in vitro, conducted between Switzerland and Australia, which has yet to be published in a peer-reviewed scientific journal. It is available on the pre-publication server MedRxiv.

Omicron is not neutralized by most therapeutic antibodies

In their experiment, the scientists tested monoclonal antibodies equivalent to those designed by several pharmaceutical companies including casirivimab and imdevimab from Regeneron (the mixture of the two is known under the trade name of Ronapreve), cilgavimab and tixagevimab from Regeneron.AstraZeneca, sotrovimab from Vir Biotechnology and bamlanivimab from AbCellera Biologics / Eli Lilly.

Neutralization tests were performed on cultures of Vero6 cells and a strain of variant Omicron. Increasing doses of monoclonal antibodies were tested until neutralization was observed or not. Of the six monoclonal antibodies, four are unable to neutralize the variant Omicron, both of which were created by Regeneron, at the highest dose tested. Sotrovimab and tixagevimab retain neutralizing action against Omicron, but at much larger doses. It takes 1,059 ng / mL of sotrovimab and 3,490 ng / mL of tixagevimab to get rid of Omicron, compared to only 372 ng / mL and 47 ng / mL to neutralize an older variant, close to Gamma. Therefore, approximately 2.8 times more sotrovimab and 73.8 times more tixagevimab are required against Omicron.

A study by the Institut Pasteur, published on December 16, 2021, presented similar results. They observed that six therapeutic antibodies lose their potency antiviral against Omicron, including the Ronapreve. The others are between 3 to 80 times less effective against Omicron, compared to the Delta variant. These results, still preliminary, could call into question the use of monoclonal antibodies, and Ronapreve, authorized for prophylaxis in patients at risk by the ANSM (National Agency for the Safety of Medicines and Health Products), for an infection due to Omicron.

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