Omicron is now the dominant Covid-19 variant in London, new analysis suggests.
Some 51.8% of a sample of new coronavirus cases in London with specimen dates for December 11 and 12 were found to have "S gene target failure" – a way of detecting the likely presence of Omicron.
Most samples of Omicron that have been sequenced in a laboratory have been found to contain a slight but identifiable difference from other Covid-19 variants such as Delta.
This difference – a deletion in the S gene – shows up in certain laboratory PCR tests and can be used as way of estimating the spread of Omicron.
Of the 1,391 Covid-19 cases in London recorded on December 11 and 12 where the S gene status could be determined, 721 were classed as SGTF.
The figures, which have been published by the UK Health Security Agency, also show that 26.9% of a sample of detectable cases in eastern England from December 11 and 12 were classed as SGTF, along with 25.4% in south-east England and 20.8% in north-west England.
Levels were lower in all other regions, with north-east England having the lowest estimate of 6.2%.
The level for the whole of England was estimated at 24.0%.
All figures are based only on samples tested at four of the UK Lighthouse laboratories – Alderley Park, Glasgow, Milton Keynes and Newcastle – which means there are likely to be parts of the country where the prevalence of Omicron is underreported.
Health Secretary Sajid Javid refused to rule out the prospect of fresh measures over the coming weeks but insisted the steps currently in place “are the right ones”.
Asked whether more guidance would be issued – rather than legislation – he told reporters at The Gordon Hospital in Westminster: “We keep the whole situation under review. It is fast-moving, I think people understand that.
“The case numbers are still sadly rising rapidly, we have been very open about how quickly this new variant spreads, we have seen it double in terms of infections every two to three days across the country.
“In London, now, for example, it is our understanding that it is 60% of all cases already.”
Asked at the vaccination centre whether restrictions could be ruled out before the new year, Mr Javid said: “We have to observe the situation and learn more about this all the time.
“We are buying time to assess this virus and build our defences.”
Pressed on whether people should prepare for new restrictions in the new year, Mr Javid replied: “You should be preparing yourselves to get boosted.”