Official findings that Omicron may be less likely to result in serious illness than Delta offer a "glimmer of Christmas hope", the head of the UK Health Security Agency has said.
But Jenny Harries told the BBC it was too early to retract her statement that the variant was the most serious threat the UK had faced during the pandemic.
The UKHSA's findings are "preliminary", she said, and data around Omicron's impact on the elderly is still needed.
UK Covid cases have reached a new high.
A
record of 122,186 new infections were reported on Friday - while the Office for National Statistics estimates 1.74 million people in the UK had coronavirus on 19 December, up by more than 368,000 on the figure three days earlier.
This equates to 2.7% of the population or one in 35 people. In London, that figure is one in 20.
Meanwhile, the latest figures show 1,171 people with Covid or suspected Covid were admitted to hospital on Monday - the highest number since 19 February.
Responding to
UKHSA analysis that those cases with Omicron - now the UK's dominant strain - are less likely to need hospital care, Dr Harries told Radio 4's Today programme: "There is a glimmer of Christmas hope... but it definitely isn't yet at the point where we could downgrade that serious threat.
"What we have got now is a really fine balance between something that looks like a lower risk of hospitalisation - which is great news - but equally a highly transmissible variant and one that we know evades some of our immune defences, so it is a very balanced position."
The UKHSA estimates that someone with Omicron is between 31% and 45% less likely to attend A&E and 50% to 70% less likely to be admitted to hospital than an individual with the Delta variant.
However, Dr Harries warned there was much that is still unknown about Omicron.
"We don't yet know what the average length of stay for an individual is in a hospital," she said.
"We're not seeing very significant rises in intensive care utilisation or in the use of ventilation beds. Now that may be because a lot of the people who've been infected to date are actually younger people and we will see that coming through."
But if the severity of the disease is actually "significantly lower than Delta" then some of the impact on the NHS may be less severe, she added.
Office for National Statistics chief Sir Ian Diamond said there were "indications" the Omicron variant was encouraging people to adopt "safer" behaviour but it was "far too early to suggest that we will see anything other than a continued rise" in cases.
He told BBC Radio 4's World At One programme all areas of the UK, except for south-west England, were seeing increases - although in Scotland infections had "gone up just a little bit".
FULL ARTICLE - Covid: Glimmer of Christmas hope on Omicron, says Jenny Harries
