A Covid variant that has become known as “kraken” may spread almost 40 per cent faster than Britain’s currently dominant strain and could take over as the country’s most common form of the virus, health officials have said.
The variant is a mutant form of omicron, technically called XBB.1.5, which was created when two other omicron variants merged and forged a new set of mutations.
Dr Maria Van Kerkhove, the World Health Organisation’s Covid technical lead, said last week that XBB.1.5 is “the most transmissible sub-variant that has been detected yet”, with mutations allowing it to latch on to human cells and replicate easily.
XBB.1.5 increased quickly in the US and became the dominant Covid strain, but it accounted for just one in 20 Covid infections in the UK at the end of last year.
A technical briefing released by the UK Health Security Agency (UKHSA) on Wednesday revealed that “kraken” has a weekly growth advantage of 38.9 per cent when compared to the currently dominant BQ1.1 sublineage of omicron, which currently causes around half of all Covid cases in Britain.
Not yet a variant of concern
“The growth advantage associated with XBB.1.5 is biologically plausible given the combination of immune escape properties and ACE-2 affinity that are expected based on available laboratory data,” the UKHSA said.
XBB.1.5, and another emerging variant called CH.1.1, “are currently the variants most likely to predominate in the UK following BQ.1”, it added, saying it is “plausible that XBB.1.5 will cause an increase in incidence after the current wave. However, it is currently too early to confirm this trajectory”.
Omicron has diverged into a host of sub-lineages, re-combinants and mutated forms of SARS-CoV-2, but none has been sufficiently different to warrant a new Greek letter. Nicknames have emerged on social media, leading to “kraken”, which has no scientific grounding, meaning or validity.
The UKHSA only sequences a small proportion of all Covid tests but has so far only confirmed 161 known cases of XBB.1.5 in the UK, with 136 in England. The most so far have come in the North West (35) and London (27), it said.
Officials have said this analysis is early and done on a small number of tests, meaning estimates are highly uncertain and may change. In the US, for example, the Centers for Disease Control and Prevention recently revised estimated for how many cases were caused by “kraken” from 41 per cent to 18 per cent.
XBB.1.5 is now formally recognised as a variant by the UKHSA, but is not yet a variant of concern.
‘Vaccination remains best defence’
Dr Meera Chand, the UKHSA director of clinical and emerging infections, said: “Through our genomic surveillance, we continue to see evolution of variants in the omicron family. UKHSA is constantly monitoring the situation and working to understand the implications for public health.
“Vaccination remains our best defence against future Covid-19 waves, so it is still as important as ever that people come take up all the doses for which they are eligible as soon as possible.”
An assessment from the WHO, published on Wednesday, said XBB.1.5 “may contribute to increases in case incidence globally” based on its growth rate advantage and genetic characteristics.
The WHO is hoping to get better growth rate estimates in a week, to have data on whether XBB.1.5 can evade prior immunity in a fortnight, and to know whether it causes more or less severe disease in a month.
There is as yet no real-world data on whether the variant is more severe or evades immunity from either natural infection or vaccination. However, lab studies indicate that it is as immune evasive as other XBB variants.