‘Significant immune evasion’
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 mash-up 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.
“This is of concern for us because we need to ensure that the vaccines that are in use worldwide remain effective at preventing severe disease and death.”
Dr Jesse Bloom, an expert on viral evolution at the Fred Hutchinson Cancer Research Center in Seattle, added that 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 that reduced global surveillance networks means it is harder to track and understand this swarm of new sub-variants.
“There are millions of cases being recorded each week. But surveillance has declined, testing has declined, sequencing has declined – that in turn has limited our ability as an organisation, with our expert networks around the world, to assess these [variants],” Dr Van Kerkove said.
“Countries need to be in a position to conduct surveillance and deal with increasing cases.”
New restrictions unlikely
In Singapore, the health minister has said that a new wave has been triggered by XBB. Cases have jumped from around 3000 a day in late September to 8500 on October 18, although the number of people in intensive care has remained relatively steady.
Prof 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,” he told the Telegraph. “However other aspects of the immune response less related to antibodies remain strong in preventing severe disease.
“In reality, reintroduction of blunt community curbs will only be needed if hospitals are threatened because of increasing severe disease. More mild cases should not be a trigger.”
Dr Amesh Adalja, of the Johns Hopkins University Center for Health Security in America, added: “It’s important to remember that immunity is not an on or off switch. It’s a spectrum of protection.
“Even if XBB can get around some immunity that’s been provided by prior infections, it will still be unable to cause severe disease because other aspects of immunity such as T-cells are really really good nevertheless… we’re shifting Covid-19 to the outpatient side – to something that doesn’t require hospitalisation.”
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 is not comparable to previous jumps.
“People are recording three, four, fivefold changes and calling that immune evasion. Yes it’s relative, but it’s small. Remember beta versus Wuhan was at least 10 to 15 times, while omicron versus Wuhan was about 30 times.”
