Planas D, Saunders N, Maes P, Guivel-Benhassine F, Planchais C, Buchrieser J, Bolland WH, Porrot F, Staropoli I, Lemoine F, Péré H, Veyer D, Puech J, Rodary J, Baele G, Dellicour S, Raymenants J, Gorissen S, Geenen C, Vanmechelen B, Wawina-Bokalanga T, Martí-Carreras J, Cuypers L, Sève A, Hocqueloux L, Prazuck T, Rey FA, Simon-Loriere E, Bruel T, Mouquet H, André E, Schwartz O.
The SARS-CoV-2 Omicron variant was first identified in November 2021 in Botswana
and South Africa1–3. It has since spread to many countries and is expected to rapidly
become dominant worldwide. The lineage is characterized by the presence of
around 32 mutations in spike—located mostly in the N-terminal domain and the
receptor-binding domain—that may enhance viral fitness and enable antibody
evasion. Here we isolated an infectious Omicron virus in Belgium from a traveller
returning from Egypt. We examined its sensitivity to nine monoclonal antibodies that
have been clinically approved or are in development4, and to antibodies present in 115
serum samples from COVID-19 vaccine recipients or individuals who have recovered
from COVID-19. Omicron was completely or partially resistant to neutralization by all
monoclonal antibodies tested. Sera from recipients of the Pfizer or AstraZeneca
vaccine, sampled five months after complete vaccination, barely inhibited Omicron.
Sera from COVID-19-convalescent patients collected 6 or 12 months after symptoms
displayed low or no neutralizing activity against Omicron. Administration of a booster
Pfizer dose as well as vaccination of previously infected individuals generated an
anti-Omicron neutralizing response, with titres 6-fold to 23-fold lower against
Omicron compared with those against Delta. Thus, Omicron escapes most
therapeutic monoclonal antibodies and, to a large extent, vaccine-elicited antibodies.
However, Omicron is neutralized by antibodies generated by a booster vaccine dose.