Covid-19: Omicron variants, champions of immune escape

From his emergencethe variant Omicron (B.1.1.529) demonstrated a great ability to evade neutralization by antibody because of the many mutations carried by its protein S. The latter was gradually replaced by BA2, responsible for the sixth vague epidemic last April, then by BA5 which feeds the current wave – the 7^e – which continues to grow. How well do BA4 and BA5 evade antibodies? Researchers have answers to this question.

Disarmed antibodies against Omicron BA4 and BA5 variants

BA2, BA4 and BA5 have mutations on their S protein which were absent in BA1, this is one of the reasons for their epidemiological success. Among them, F486V gives these variants a resistance class 1 and 2 neutralizing antibodies, according to a study recently published in Nature. Class 1 neutralizing antibodies bind only to the RBD in “open” configuration, and those of class 2 on the open or closed RBD. This mutation decreases the affinity of virus for its receptor – a problem solved by the presence of another mutation, R493Q, which restores the lost affinity.

In another studyGerman researchers tested the neutralizing abilities of vaccine antibodies after three doses of Pfizer : the neutralizing power of the antibodies is eight times lower with respect to BA4 and BA5 than that observed with B.1.1.529. Therapeutic antibodies are a complementary treatment to anti-Covid vaccines and several formulations already authorized lose their effectiveness against BA4/5.

Sotrovimab (trade name Xevudy), effective against BA1, significantly loses potency against BA2 and BA4/5. Cilgavimab (trade name Evusheld) is effective against all Omicron subvariants except BA.1. Only bebtelovimab, which obtained an emergency use authorization from the FDA in February 2022, but not available in Europe, represents an effective treatment against all variants of the Omicron family.

While the summer will be placed under the sign of the Covid, the respect for barrier gestures is more important than ever. In case of symptoms and with a test of screening positive for the Covid-19, isolation is required. In closed and crowded places, and on public transport, wearing a mask is strongly recommended.