UK researchers have analysed the likely impact that a Covid booster shot will have on Omicron and say it could provide around 85% protection against severe illness.
The protection is a bit less than vaccines gave against earlier versions of Covid.
But it means the top-up dose should still keep many people out of hospital.
It comes as a record 861,306 number of booster jabs and third doses were given in the UK on Thursday.
Vaccines help teach the body how to fight Covid. But the current ones in use were not designed to combat the heavily-mutated Omicron variant, meaning they are not a perfect match.
To get round that, people in the UK are being advised to have a booster dose to build up higher antibody levels to fight the virus.
Antibodies can stick onto the virus to stop it entering cells and replicating.
Studies have suggested a 20 to 40-fold reduction in the ability of these antibodies to take out the virus in double-vaccinated people.
The preliminary work from Imperial assumes there will be a drop in vaccine efficacy against Omicron.
Even with a booster, protection against severe disease from Omicron may be around 80 to 85.9%, compared to around 97% for Delta – the other variant that is currently dominant in the UK.
However, there are other parts of the immune system, such as T cells, that can fight Covid too.
Cases of Omicron are rising – and there’s more to come.
The UK has recorded 3,201 new cases of the Omicron variant, up from yesterday’s figure of 1,691.
It takes the total number of confirmed Omicron cases in the UK to 14,909 – although the true figure is believed to be much higher because not all labs can detect the variant and not everyone will come forward for testing.