July 09, 2021
Bulletin interne de l'Institut Pasteur
Analysis of the sensitivity of the Delta variant to monoclonal antibodies and sera from convalescent and vaccinated individuals
The Delta variant was detected for the first time in India in October 2020 and has since spread throughout the world. It is now dominant in many countries and regions (India, the UK, Portugal, Russia, etc.) and is predicted to be the most prevalent variant in Europe within weeks or months. Epidemiological studies have shown that the Delta variant is more transmissible than other variants. Scientists from the Institut Pasteur (CNRS joint unit), in collaboration with Hôpital Européen Georges Pompidou (part of the Paris Public Hospital Network or AP-HP), Orléans Regional Hospital and Strasbourg University Hospital, studied the sensitivity of the Delta variant to monoclonal antibodies used in clinical practice to prevent severe forms of the disease in people at risk, as well as to neutralizing antibodies in the sera of individuals previously infected with SARS-CoV-2 or vaccinated. They compared this sensitivity with that of the virus previously circulating in France (known as the Alpha or "British variant") and the "South African variant" (Beta variant).
The scientists demonstrated that the Delta variant is less sensitive to neutralizing antibodies than the Alpha variant. Three of the four therapeutic monoclonal antibodies tested are effective against the Delta variant, but one of them (Bamlanivimab) loses its antiviral activity. The scientists demonstrated that sera from convalescent patients collected up to 12 months post symptoms were 4 fold less potent against the Delta variant, relative to the Alpha variant. They also studied sera from people vaccinated with two doses of the Pfizer or AstraZeneca vaccine: their sera effectively neutralized the Delta variant, although efficacy was slightly lower than against the Alpha variant. Sera from individuals who had received a single dose of vaccine (Pfizer or AstraZeneca) were inactive or barely active against the Delta and Beta variants. In summary, the Delta variant is slightly more resistant to neutralizing antibodies than the Alpha variant.