The sensitivity of Omicron to antibodies is currently being studied in comparison with the currently dominant Delta variant.
The new COVID-19 Omicron variant is more transmissible than the Delta variant. However, its biological characteristics are still relatively unknown.
The study on this variant was published in 'Nature Journal'.
In South Africa, the Omicron variant replaced other viruses within a few weeks and caused a sharp increase in the number of diagnosed cases. Analyzes in several countries indicate that the doubling time of cases is about 2 to 4 days. Omicron has been detected in dozens of countries, including France, and became dominant at the end of 2021.
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 (Louvain, Belgium), the Orléans Regional Hospital, the Georges Pompidou European Hospital (AP-HP) and Inserm, studied the sensitivity of Omicron to antibodies compared to the currently dominant Delta variant.
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The objective of the study was to characterize the effectiveness of therapeutic antibodies, as well as antibodies developed by individuals previously infected with SARS-CoV-2 or vaccinated, to neutralize this new variant.
Scientists at 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 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 previously vaccinated or exposed to SARS-CoV-2 were used to study the sensitivity of the Omicron variant.
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 Bamlanivimab / Etesevimab (a combination developed by Lilly), Casirivimab / Imdevimab (a combination developed by Roche and known as Ronapreve) and Regdanvimab (developed by Celtrion) antibodies no longer had an antiviral effect against Omicron. The combination Tixagevimab / Cilgavimab (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 antibody resistance. Most of the therapeutic monoclonal antibodies currently available against SARS-CoV-2 are inactive," commented Olivier Schwartz, final co-author of the study and Head of the Virus and Immunity Unit at the Institut Pasteur.
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 vaccine, taken five months after vaccination, barely neutralized the Omicron variant. But sera from people who received a booster dose of Pfizer, tested one month after vaccination, were still effective against Omicron.
However, five to 31 times more antibodies were needed to neutralize Omicron, compared with Delta, in cell culture tests. These findings help shed light on the continued effectiveness of vaccines in protecting against severe forms of the disease.
"Now we must study the duration of protection of the booster dose. Vaccines will probably become less effective in providing protection against the spread of the virus, but they must continue to protect against severe forms," said Olivier Schwartz.
"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 possible solutions. While KU Leuven was able to describe the former case of Omicron infection in Europe thanks to the Belgian genome surveillance system, our collaboration with the Institut Pasteur in Paris enabled us to carry out this study in record time. Much work remains to be done, but thanks to the support of the European Union Health Emergency Preparedness and Response Authority (HERA), we have clearly reached a point where scientists from the best centers can work in synergy and advance towards a better understanding and more effective management of the pandemic ”, commented Emmanuel André , co-author of the study, a professor of medicine at KU Leuven (Katholieke Universiteit Leuven) and head of the National Reference Laboratory and the genome surveillance network for COVID-19 in Belgium.
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Scientists concluded that the numerous mutations in the spike protein of the Omicron variant allowed it to largely evade the immune response. Research is underway to determine why this variant is more transmissible from one individual to another and to analyze the long-term effectiveness of a booster dose.
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