As Covid grinds on, Omicron mutations raise new infection threats

Omicron sub-variants are showing signs of “increased transmissibility and properties of immune escape”, the World Health Organisation has warned, but reduced surveillance has limited efforts to understand the ramifications.

Dr Maria Van Kerkhove, the head of the UN agency’s technical team for Covid, said more than 300 versions of Omicron are now circulating globally. These are not causing more severe disease, but they are developing qualities “of concern”.

Although no single variant is currently dominant, three are spreading quickly: XBB, which has driven a new wave of infections in Singapore, and BQ.1 and BQ.1.1, which are spreading in Europe and are now responsible for about 11 per cent of cases in the United States.

Available data suggests XBB, which has been spotted in 26 countries, may be the best at evading immunity. In one study by researchers in China, the variant partially evaded antibodies generated by a previous infection with BA.5, an older Omicron sub-variant.

Van Kerkhove suggested this could be because it is a recombinant variant. Unlike BQ.1 and BQ1.1, which are descendants of BA.5, XBB is a mashup of two Omicron sub-variants.

“We do know that this recombinant has a significant growth advantage,” she said. “We have one study that is based on a pseudo virus, so not a live virus, that is analysing antibody escape. And it’s showing significant immune evasion.

Dr Jesse Bloom, an expert on viral evolution at the Fred Hutchinson Cancer Research Centre in Seattle, added variants are evolving “strikingly rapidly” and it is “too early to predict” which one will have the biggest impact over winter.

But the WHO warned reduced global surveillance networks means it is harder to track and understand this swarm of new sub-variants.

“Countries need to be in a position to conduct surveillance and deal with increasing cases.”

In Singapore, the health minister has said a new wave has been triggered by XBB. Cases have jumped from about 3000 a day in late September to 8500 on October 18, although the number of people in intensive care has remained relatively steady.

Professor Dale Fisher, a professor in infectious diseases at the National University of Singapore, said the variant is unlikely to trigger a set of new restrictions.

“It seems to have capacity to partially evade the immune capacity to prevent infection and this is linked to a surge in mild cases.

“However other aspects of the immune response less related to antibodies remain strong in preventing severe disease.

There has been some debate about whether the new sub-variants should be re-categorised as a new letter of the Greek alphabet or not.

But Professor Ravi Gupta, a professor of clinical microbiology at the University of Cambridge, said they still have a “very common set” of characteristics and appear to be evolving in the same direction.

“That variants are picking up very similar sets of mutations is a sign that there’s quite a lot of population level immunity out there that the virus is trying to overcome,” he said.

“It would take a ‘super hot’ variant to take over the world.”

He added that the increased immune evasion was not comparable to previous jumps.