Every person infected with the Omicron COVID variant is believed to be passing it on to between three and five others on average, a senior government scientist has said.
Dr Susan Hopkins, the UK Health Security Agency’s chief medical adviser, told MPs on the Commons health committee that for Omicron, the R value in the UK is between 3 and 5.
The number of cases is spreading rapidly – doubling in size every two days.
The current R value of the Delta epidemic in the UK is estimated to be between 1.1 and 1.2.
A million could be isolating with COVID on Christmas Day – live COVID updates
Dr Hopkins also told the hearing that reliable data on Omicron will not be available until the week between Christmas and New Year at the earliest, and may not appear before early January.
There are currently 15 people being treated in hospital with Omicron, she added.
That number needs to rise to 250 before any meaningful assessment can be made of the variant’s severity, and of vaccine effectiveness.
Dr Hopkins said measures are being taken to improve “data linkage” and new figures would be released on Thursday afternoon.
England’s chief medical officer, Professor Chris Whitty, clarified: “The real number will be much bigger than that (15). That is simply the number who are proven, just to be clear.”
Daily COVID hospital admissions could exceed record set in January
Prof Whitty also said it is “entirely possible” that the number of daily hospital admissions because of the Omicron variant could exceed the record set for COVID in January.
Committee chair, Jeremy Hunt MP, asked him if the previous peak – 4,583 – could be exceeded.
He replied: “It is possible – because this is going to be very concentrated – that even if it is milder, because it’s concentrated over a short period of time, you could end up with a higher number than that going into hospital on a single day – that is entirely possible.”
But he added that it may be fewer than than, and there are still “huge uncertainties”.
Prof Whitty said the time people spend in hospital is an important indicator of pressure on the NHS.
He explained: “One of the things that really matters to the NHS is how long people stay.
“If, for example, people stay in hospital for a shorter period, because they’re protected by prior vaccination, that means that the total number could still be lower even if the peak number per day is higher.”
Predicting the effect on the NHS over the coming month or so is not easy, he said.
“The range of possibilities is really quite wide and that’s why it’s very difficult to make definitive views about where the NHS is going to end up in the next four weeks.”
He added: “It is possible that, with a boost, we’re better off with Omicron than we are with two vaccines with Delta for severe disease. I don’t think that’s likely for infection, but it’s possible, but we honestly don’t know.”
Omicron may peak quickly – and fall quickly too
Prof Whitty added that the “whole point” about Omicron is that it is “going to be really concentrated in a very short period of time, very possibly”.
Omicron may also peak quickly, and fall away quickly too, the CMO told MPs.
“I think what we will see with this – and I think we are seeing it in South Africa – is that the upswing will be incredibly fast, even if people are taking more cautious actions, as they are.
“That will help slow it down, but it’s still going to be very fast.
“It’ll probably therefore peak really quite fast. My anticipation is it may then come down faster than previous peaks but I wouldn’t want to say that for sure. I’m just saying that that is a possibility.”