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.
The modelling, from the team at Imperial College London, is based on limited information on Omicron.
The researchers say there is a high degree of uncertainty until more real-world information is gathered about this new variant that is spreading quickly.