People catching Omicron are 50% to 70% less likely to need hospital care compared with previous variants, a major analysis says.
The UK Health Security Agency says its early findings are "encouraging" but the variant could still lead to large numbers of people in hospital.
The health secretary said it was "too early" to determine "next steps".
The study also shows the jab's ability to stop people catching Omicron starts to wane 10 weeks after a booster dose.
Protection against severe disease is likely to be far more robust.
The report comes hot on the heels of data from South Africa, Denmark, England and Scotland which all pointed to reduced severity.
The latest analysis is based on all cases of Omicron and Delta in the UK since the beginning of November, including 132 people admitted to hospital with the variant. There have also been 14 deaths in people within 28 days of catching Omicron.
The report shows people catching Omicron are:
- *31% to 45% less likely to go to A&E
- *50% to 70% less likely to be admitted to hospital for treatment
However, a milder virus could still put pressure on hospitals because it spreads so fast.
The issue remains that any benefit of a milder virus could be wiped out by large numbers of people catching Omicron. The UK has set another daily Covid record with 119,789 confirmed cases. There were a further 147 deaths within 28 days of a positive test.
There is also uncertainty about what will happen when Omicron reaches older age groups because most of those catching it and going into hospital so far have been under the age of 40.