UK's Omicron Covid variant cases nearly double in a day, tally at 817

The number of cases of the Omicron variant of COVID-19 in Britain has nearly doubled in one day after a further 249 cases were confirmed on Thursday, bringing the UK total to 817.

The UK Health Security Agency (UKHSA) said if the growth rate and doubling time continue at the rate seen in the last two weeks, they expect to see at least 50 per cent of coronavirus (COVID-19) cases to be caused by Omicron variant in the next two to four weeks.

Prime Minister Boris Johnson had earlier said that the variant's doubling rate could be between two to three days as he announced tougher measures of expanded compulsory face masks in indoor settings, work from home guidance and COVID vaccine certification for entry into venues.

"It is increasingly evident that Omicron is highly infectious and there is emerging laboratory and early clinical evidence to suggest that both vaccine-acquired and naturally acquired immunity against infection is reduced for this variant. It is therefore absolutely critical that we all do everything that we can to help break the chains of transmission and slow the spread of this new variant, said UKHSA Chief Medical Advisor Dr Susan Hopkins.

"Vaccination is critical to help us bolster our defences against becoming severely ill from this new variant please get your first, second, third or booster jab without delay, she said.

The agency said that whilst there is insufficient data to quantify either vaccine effectiveness or risk of reinfection in the UK exactly, the observed growth, case distribution and early analyses in both South Africa and the UK are consistent with some loss of immune protection against infection. New studies are being undertaken to assess this further, it added.

In a related study, early data has suggested the new variant could result in less severe disease than previous waves. However, Tim Spector, lead scientist on the UK's Zoe app-based COVID Study, warned against complacency.

"Even with Omicron appearing to be more transmissible than Delta, early signs, including new reports from Zoe users, show that it is breaking through in vaccinated people, but it's causing milder cold-like symptoms. However, this is not a reason to be relaxed about Omicron, said Spector, professor of genetic epidemiology at King's College London and co-founder of the Zoe app that tracks the spread of COVID-19.

"COVID is unpredictable and, even if most only feel like they've got a cold, there are far more long-term risks than a cold carries. If numbers skyrocket, it doesn't matter if the percentage of people being hospitalised or dying remain low - it's about volume, not percentages, he said.

The Zoe study, whose incidence figures are based on reports from around 650,000 weekly contributors, has introduced a new feature into the app that allows people to share their Omicron experiences and symptoms.