Dr Jenny Harries, chief executive of the UK Health Security Agency (UKHSA), told BBC Radio 4â€™s Today programme that people could do their bit by reducing the number of social contacts they have.
She said that even if our â€œvaccines appear to be effective, but we find that the variant is more highly transmissible, having lowish grade infection, but in very large numbers of the population, (it) could still be a significant impact on our hospitals.
â€œAnd of course, our behaviours in winter and particularly around Christmas we tend to socialise more so I think all of those will need to be taken into account.â€
Asked about working from home, she said: â€œWeâ€™ve seen that not everybody has gone back to work and Iâ€™d like to think of it more in a general way, which is if we all decrease our social contacts a little bit, actually that helps to keep the variant at bay.
â€œSo I think being careful, not socialising when we donâ€™t particularly need to and particularly going and getting those booster jobs which, of course, people will now be able to have at a three-month interval from their primary course.â€
PM Boris Johnson defended Englandâ€™s new coronavirus rules, which came into force this morning.
â€œThe measures taking effect today are proportionate and responsible, and will buy us time in the face of this new (Omicron) variant,â€ he said.
â€œVaccines and boosters remain our best line of defence, so it is more important than ever that people come forward when eligible to get boosted.â€