Omicron: resistant to most monoclonal antibodies but neutralized by a booster dose

The Omicron variant was detected for the first time in South Africa in November 2021 and has since spread to many countries. It is expected to become the dominant variant within a few weeks or months. Initial epidemiological studies show that the Omicron variant is more transmissible than the currently dominant virus (the Delta variant). It is capable of spreading to individuals who have received two vaccine doses and to previously infected individuals. 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. The scientists then analyzed the blood of people who had received two doses of the Pfizer or AstraZeneca vaccine. Five months after vaccination, the antibodies in the blood were no longer capable of neutralizing Omicron. This loss of efficacy was also observed in individuals who had been infected with SARS-CoV-2 within the past 12 months. Administering a booster dose of the Pfizer vaccine or a single vaccine dose in previously infected individuals led to a significant increase in antibody levels that was sufficient to neutralize Omicron. Omicron is therefore much less sensitive to the anti-SARS-CoV-2 antibodies currently used in clinical practice or obtained after two vaccine doses.
 

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