Booster dose neutralizes Omicron variant, study finds

Five to 31 times more antibodies were needed to neutralize Omicron, according to study (representative)


An international team of researchers recently investigated the antibody sensitivity of Omicron against the currently dominant Delta variant. The study on this variant was published in the “Natural Diary”.

The new COVID-19 Omicron variant is more transmissible than the Delta variant. However, its biological characteristics are still relatively unknown.

In South Africa, the Omicron variant replaced other viruses within weeks and led to a sharp increase in the number of diagnosed cases. Analyzes in various countries indicate that the doubling time for cases is around 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 Regional Hospital of Orleans, the European Hospital Georges Pompidou (AP-HP) and Inserm, studied the sensitivity of Omicron to antibodies compared to the currently dominant Delta variant.

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.

KU Leuven scientists isolated the Omicron variant of SARS-CoV-2 from a nasal sample of a 32-year-old woman who developed mild 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 vaccinated or previously exposed to SARS-CoV-2 were used to study the sensitivity of the Omicron variant.

The scientists used rapid neutralization tests, developed by the Virus and Immunity Unit of the Pasteur Institute, on the isolated sample of the Omicron virus. This multidisciplinary collaboration also involved virologists from the Institut Pasteur and specialists in the analysis of viral evolution and protein structure, as well as teams from the Orléans University Hospital and the Georges Pompidou European Hospital in Paris.

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 (combination developed by Lilly), Casirivimab/Imdevimab (combination developed by Roche and known as Ronapreve) and Regdanvimab (developed by Celtrion) no longer had any antiviral effect against Omicron. The Tixagevimab/Cilgavimab combination (developed by AstraZeneca under the name Evusheld) was 80 times less effective against Omicron than against Delta.

“We have demonstrated that this highly transmissible variant has acquired significant antibody resistance. 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 blood from patients previously infected with COVID-19, taken 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 the sera of individuals who received a booster dose of Pfizer, analyzed one month after vaccination, remained effective against Omicron.

Five to 31 times more antibodies were nevertheless required to neutralize Omicron, compared to Delta, in cell culture tests. These results help shed light on the continued effectiveness of vaccines in protecting against severe forms of the disease.

“We now need to study the duration of protection of the booster dose. Vaccines are probably becoming less effective in offering protection against contracting the virus, but they should continue to protect against severe forms,” explained Olivier Schwartz.

“This study shows that the Omicron variant hinders 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. While KU Leuven was able to describe the first case of Omicron infection in Europe thanks to the Belgian genome surveillance system, our collaboration with the Institut Pasteur in Paris allowed us to carry out this study in record time,” comments Emmanuel Andre, co-last author of the study, professor of medicine at KU Leuven (Katholieke Universiteit Leuven) and head of the national reference laboratory and genome surveillance network for COVID-19 in Belgium.

“There is still a lot of work to do, but thanks to the support of the European Union’s Health Emergency Preparedness and Response Authority (HERA), we have clearly 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,” added Emmanuel.

The scientists concluded that the many mutations in the spike protein of the Omicron variant allow it to largely evade the immune response. Ongoing research is being conducted to determine why this variant is more transmissible between individuals and to analyze the long-term effectiveness of a booster dose.

(This story has not been edited by NDTV staff and is auto-generated from a syndicated feed.)

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