New Omicron subvariant largely evades neutralising antibodies: Lancet study

The BA.2.75.2 variant of Omicron largely evades neutralising antibodies in the blood and is resistant to several Covid-19 antibody therapies, according to a study published in The Lancet Infectious Diseases journal.

The findings by researchers at Karolinska Institutet, Sweden suggest a risk of increased SARS-CoV-2 infections this winter, unless the new updated bivalent vaccines help to boost immunity in the population.

"While antibody immunity is not completely gone, BA.2.75.2 exhibited far more dramatic resistance than variants we've previously studied, largely driven by two mutations in the receptor binding domain of the spike protein," said the study's corresponding author Ben Murrell, an assistant professor at Karolinska Institutet.

The SARS-CoV-2 virus uses the spike protein to enter and infect the human cells.

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The study shows that antibodies in random serum samples from 75 blood donors in Stockholm, Sweden were approximately only one-sixth as effective at neutralising BA.2.75.2 compared with the now-dominant variant BA.5.

The serum samples were collected at three time points: In November last year before the emergence of Omicron, in April after a large wave of infections, and at the end of August to early September after the BA.5 variant became dominant.

Only one of the clinically available monoclonal antibody treatments that were tested, bebtelovimab, was able to potently neutralise the new variant, according to the researchers.

Monoclonal antibodies are used as antiviral treatments for people at high risk of developing severe Covid-19.

BA.2.75.2 is a mutated version of another Omicron variant, BA.2.75. Since it was first discovered earlier this year, it has spread to several countries but so far represents only a minority of registered cases.

"We now know that this is just one of a constellation of emerging variants with similar mutations that will likely come to dominate in the near future," said Murrell adding "we should expect infections to increase this winter."

However,the researchers noted that it is unclear whether these new variants will drive an increase in hospitalisation rates.

While current vaccines have, in general, had a protective effect against severe disease for Omicron infections, they said, there is not yet data showing the degree to which the updated Covid vaccines provide protection from these new variants.

"We expect them to be beneficial, but we don't yet know by how much," Murrell added.