The Omicron variant was detected for the first time in South Africa in November 2021 and has since spread to many countries.

Initial epidemiological studies show that the Omicron variant is more transmissible than the currently dominant virus (the Delta variant).

Scientists from the Institut Pasteur and the Vaccine Research Institute, in collaboration with KU Leuven (Leuven, Belgium), Orléans Regional Hospital, Hôpital Européen Georges Pompidou (AP-HP), Inserm and the CNRS, studied the sensitivity of the Omicron variant to monoclonal antibodies used in clinical practice to prevent severe forms of the disease in people at risk, as well as to antibodies in the blood of individuals previously infected with SARS-CoV-2 or vaccinated.

They compared this sensitivity with that of the Delta variant.

The scientists demonstrated that Omicron is much less sensitive to neutralizing antibodies than Delta.

Initial epidemiological studies demonstrate that the Omicron variant is more transmissible than the Delta variant.

In a new study supported by the European Union’s Health Emergency Preparedness and Response Authority (HERA), scientists from the Institut Pasteur and the Vaccine Research Institute, in collaboration with KU Leuven (Leuven, Belgium), Orléans Regional Hospital, Hôpital Européen Georges Pompidou (AP-HP) and Inserm, studied the sensitivity of Omicron to antibodies compared with the currently dominant Delta variant.

The aim of the study was to characterize the efficacy of therapeutic antibodies, as well as antibodies developed by individuals previously infected with SARS-CoV-2 or vaccinated, in neutralizing this new variant.

The scientists from KU Leuven isolated the Omicron variant of SARS-CoV-2 from a nasal sample of a 32-year-old woman who developed moderate COVID-19 a few days after returning from Egypt.

The isolated virus was immediately sent to scientists at the Institut Pasteur, where therapeutic monoclonal antibodies and serum samples from people who had been vaccinated or previously exposed to SARS-CoV-2 were used to study the sensitivity of the Omicron variant.

The scientists used rapid neutralization assays, developed by the Institut Pasteur’s Virus and Immunity Unit, on the isolated sample of the Omicron virus.

The scientists began by testing nine monoclonal antibodies used in clinical practice or currently in preclinical development.

Six antibodies lost all antiviral activity, and the other three were 3 to 80 times less effective against Omicron than against Delta.

The Tixagevimab/Cilgavimab combination (developed by AstraZeneca under the name Evusheld) was 80 times less effective against Omicron than against Delta.

“We demonstrated that this highly transmissible variant has acquired significant resistance to antibodies.

Most of the therapeutic monoclonal antibodies currently available against SARS-CoV-2 are inactive,” comments Olivier Schwartz, co-last author of the study and Head of the Virus and Immunity Unit at the Institut Pasteur.

The scientists observed that the blood of patients previously infected with COVID-19, collected up to 12 months after symptoms, and that of individuals who had received two doses of the Pfizer or AstraZeneca vaccine, taken five months after vaccination, barely neutralized the Omicron variant.

Five to 31 times more antibodies were nevertheless required to neutralize Omicron, compared with Delta, in cell culture assays.

“This study shows that the Omicron variant hampers the effectiveness of vaccines and monoclonal antibodies, but it also demonstrates the ability of European scientists to work together to identify challenges and potential solutions.

The scientists concluded that the many mutations in the spike protein of the Omicron variant enabled it to largely evade the immune response?