The UK will exceed more than one million Omicron infections by the end of the month if current trends continue unchanged, the UK Health Security Agency (UKHSA) said on Friday.
It also expects Omicron to become the dominant variant across the whole UK by mid-December.
Earlier on Friday, First Minister Nicola Sturgeon said the Scottish Government expects Omicron to overtake Delta as the dominant strain in Scotland “within days, not weeks”.
She said: “Omicron right now is rising exponentially, indeed what we are seeing in the data just now is perhaps the fastest exponential growth that we have seen in this pandemic so far.
“If that continues, and we have no reason at this stage to believe that it won’t, Omicron is going to very quickly overtake Delta as the dominant strain in Scotland.”
Meanwhile, UKHSA analysis of 581 people with confirmed Omicron cases showed the AstraZeneca and Pfizer vaccines provided “much lower” levels of protection against Omicron when compared with the Delta variant.
But the UKHSA said that preliminary data showed vaccine effectiveness “considerably increased” in the early period after a booster dose, providing around 70 to 75% protection against symptomatic infection.
Dr Mary Ramsay, head of immunisation at the UKHSA, said: “These early estimates should be treated with caution but they indicate that a few months after the second jab, there is a greater risk of catching the Omicron variant compared to Delta strain.
“The data suggest this risk is significantly reduced following a booster vaccine, so I urge everyone to take up their booster when eligible. We expect the vaccines to show higher protection against the serious complications of Covid-19, so if you haven’t yet had your first two doses please book an appointment straight away.”
Separate modelling in a Scottish Government evidence paper showed infections could surge to as many as 25,000 a day in the worst case scenario in Scotland.
The upper range of the document’s worst-case scenario projection for the Omicron variant falls just short of 25,000 cases a day by December 20, while the most-likely range of the worst-case scenario will see cases hit a little over 15,000.
In the best-case scenario, cases will peak at just over 1250.