Researchers stressed the results, while “encouraging”, are based on limited early data and have yet to be peer reviewed.
Analysis from Imperial College London also released on Wednesday found a 15 to 20 per cent lower risk of hospitalisation from Omicron compared to Delta, based on data from England.
It comes as the number of new Covid-19 cases in the UK reached above 100,000 for the first time, at 106,122.
And more than 20,000 probable cases of the Omicron variant have now been recorded in Scotland, with 20 people admitted to hospital.
A record 78,146 booster and third vaccines doses were logged in Scotland on Wednesday, as Nicola Sturgeon warned that despite the encouraging study, measures must continue to suppress the virus while the jag campaign continues.
The study, part of the EAVE II (Early Pandemic Evaluation and Enhanced Surveillance of Covid-19) project and involving researchers from Edinburgh and Strathclyde Universities and Public Health Scotland, looked at data across almost the entire Scottish population.
It found a booster vaccine dose may reduce the risk of symptomatic infection by 57 per cent.
But just two doses of vaccine are “significantly” less effective against the new variant than against previous strains.
Study authors examined 23,840 probable cases of the Omicron variant in Scotland as of December 19, based on S gene dropout, a proxy for genomic sequencing of the variant.
In that time almost 47 hospital admissions were expected, based on outcomes observed with the Delta variant. But just 15 were recorded, suggesting a possible two-thirds lower risk of hospitalisation.
However, Chris Robertson, professor of public health epidemiology at Strathclyde University, stressed the results have “major statistical and epidemiological caveats”.
“The level of hospital admissions that we've got following a positive test are actually much lower than we expected in the S negative [suspected Omicron] infections, assuming that they had exactly the same pattern as we've observed previously for the Delta infections,” he said.
But data for over-60s and unvaccinated people is limited, and these groups may have worse outcomes.
The results may also change if the Omicron variant turns out to cause a more delayed reaction than Delta, which has not been observed yet.
On top of this, Prof Robertson said researchers cannot yet know how long the protective effect of booster doses will last, which may lead to worse outcomes in future as immunity wanes.
Dr Jim McMenamin, Public Health Scotland’s national Covid-19 incident director, said the results were “qualified good news”.
“It's important that we don't get ahead of ourselves,” he said.
"The potentially serious impact of Omicron on a population level can't be underestimated.
“A smaller proportion of a much greater number of cases that might ultimately require treatment can still mean a substantial number of people who might experience severe Covid infections that could lead to potential hospitalisation.”
Mark Woolhouse, professor of infectious disease epidemiology at Edinburgh University, added: “An individual infection, particularly in our quite well-protected Scottish population, could be relatively mild for the vast majority of people.
“But the potential for all these infections to come along at once and therefore put serious strain on the NHS remains.”
Scottish Government ministers repeated calls for the public to follow Covid-19 guidance to protect the NHS on Wednesday, after Ms Sturgeon announced a series of new curbs on events, hospitality and leisure to come into force after Christmas.
A wave of events have been cancelled, with the Irn-Bru Carnival set to end on Christmas Eve rather than January 16, the pantomime season cut short and ten out of 12 Scottish Premiership clubs supporting a move to bring forward the winter break in a bid to avoid playing matches without spectators.
Deputy First Minister John Swinney said the Government would “consider” changing self-isolation rules in Scotland, as the requirement in England was reduced from ten to seven days, providing two lateral flow tests return negative results.
The Pfizer Covid vaccine has also been approved for use in vulnerable primary school children in the UK following an extensive review of safety data from the Medicines and Healthcare products Regulatory Agency (MHRA).
The Joint Committee on Vaccination and Immunisation (JCVI) has now advised a low-dose version of the vaccine for children aged five to 11 who are clinically vulnerable, or a household contact of someone who is immunosuppressed. They should be offered a primary course of vaccination – usually two doses.
Around 330,000 children in the UK are thought to be eligible.
New analysis from Imperial College London also suggests Omicron may carry a lower risk of hospitalisation than Delta.
Individuals infected with the new variant are 15-20 per cent less likely to visit hospital, and 40-45 per cent less likely to be hospitalised for a night or more, the new report suggests.
Researchers also stressed that a large wave of the virus may still put pressure on hospitals.
Professor Neil Ferguson, from the Imperial College, said the results were “clearly good news, to a degree".
But he said the reduction is "not sufficient to dramatically change the modelling" and the rapid spread of the variant means "there is the potential of still getting hospitalisations in numbers that could put the NHS in a difficult position".
Commenting on the EAVE II study in Scotland, Ms Sturgeon labelled the early data “encouraging”.
She emphasised that a large number of cases, even if the percentage of hospitalisations is smaller, “will still put increased pressure on the NHS and economy”.
She said the Government would continue measures to suppress the virus while the booster campaign is rolled out.
Scottish Labour’s health and Covid recovery spokesperson Jackie Baillie said the results “drive home the need for us to keep ramping up the booster programme”.
“It’s clear that vaccination remains our key tool in our fight against Covid, even with this new variant,” she said.
“It is as important as ever that we keep up efforts to contain this virus and deliver booster vaccines with the urgency needed.”