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COVID-19 | Study confirms efficacy of booster dose against Omicron

In a new study supported by the European Union Health Emergency Preparedness and Response Authority (HERA), scientists have shown that the variant Omicron it is resistant to most therapeutic antibodies, as well as to those acquired after passing the disease itself and by the vaccine. However, this variant has been found to be neutralized by a booster dose.

Thus, the researchers concluded that the numerous mutations in the protein ‘Spike’ of the variant Omicron they allowed him to largely evade the immune response.

Scientists from the Pasteur Institute and the Vaccine Research Institute (France) participated in the study, in collaboration with the KU Leuven (Leuven, Belgium), the Orleans Regional Hospital (France), the Georges Pompidou European Hospital (France) and at the National Institute of Health and Medicine Research of France, with the aim of studying the sensitivity of Ómicron to antibodies compared to the variant Delta, currently dominant.

Therefore, they sought to characterize the efficacy of therapeutic antibodies, as well as antibodies developed by individuals previously infected with SARS-CoV-2 or vaccinated, to neutralize this new variant.

Researchers at the KU Leuven isolated the Omicron variant of the SARS-CoV-2 from a nasal sample from a 32-year-old woman who developed a COVID-19 moderate a few days after returning from Egypt. The isolated virus was immediately sent to scientists at the Pasteur Institute, where therapeutic monoclonal antibodies and serum samples from people 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 Pasteur Institute’s Virus and Immunity Unit, on the Omicron virus isolated sample. Virologists from the Pasteur Institute and specialists in the analysis of viral evolution and protein structure also participated in this multidisciplinary collaborative effort, together with teams from the two aforementioned French hospitals.

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 antibodies bamlanivimab / etesevimab (a combination developed by Lilly), casirivimab / imdevimab (a combination developed by Roche and known as ‘Ronapreve’) and regdanvimab (developed by Celtrion) no longer had any antiviral effect against Ómicron. In fact, the tixagevimab / cilgavimab combination (developed by AstraZeneca under the name ‘Evusheld’) was 80 times less effective against Omicron than against Delta.

“We show that this highly transmissible variant has acquired significant resistance to antibodies. Most of the currently available therapeutic monoclonal antibodies against SARS-CoV-2 are inactive ”, comments Olivier Schwartz, co-author of the study and head of the Virus and Immunity Unit at the Pasteur Institute.

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


But serum from individuals who had received a booster dose of Pfizer, analyzed one month after vaccination, remained effective against Omicron. However, between five and 31 times more antibodies were needed to neutralize Omicron, compared to Delta, in cell culture assays. These results help shed light on the continued efficacy of vaccines in protecting against severe forms of the disease.

“Now we have to study the duration of protection from the booster dose. Vaccines are likely to become less effective in offering protection against contraction of the virus, but they should continue to protect against severe forms ”, explica Schwartz.

“This study shows that the Omicron variant hinders the efficacy of vaccines and monoclonal antibodies, but it also demonstrates the ability of European scientists to work together to identify challenges and possible solutions.”, says Emmanuel André, co-last author of the study, professor of Medicine at KU Leuven and director of the National Reference Laboratory and the COVID-19 genomic surveillance network in Belgium.

In fact, he continues, while KU Leuven was able to describe the first case of infection by Omicron in Europe using the Belgian genome surveillance system, its collaboration with the Institut Pasteur in Paris enabled this study to be carried out “In record time.”

“There is still a lot of work to be done, but thanks to the support of the European Union’s HERA, it is clear that we have now reached a point where scientists from the best centers can work in synergy and move towards better understanding and more effective management of the pandemic ”, reasons the researcher.

Research is currently underway to determine why this variant is more transmissible from one individual to another and to analyze the long-term efficacy of a booster dose.


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