Norfolk's director of public health says it is now a matter of how fast and how high coronavirus case rates will rise in the county over the winter.
And Dr Louise Smith said she is concerned that the number of people who are being admitted to the county's hospitals with the disease is increasing.
She urged people to make a renewed effort to use hand sanitiser - and for those who have not had vaccinations to get them - as coronavirus case rates in the county went up by about a third.
Covid cases in the UK are at their highest level for almost three months, with the seven-day average standing at 44,145 cases per day.
They increased from just under 331 cases per 100,000 in the week up to Wednesday, October 6 to 433.8 cases per 100,000. That was above the England average of 424.
Dr Smith said: "Cases were fairly stable through August and September, when we had about 300 cases a day.
"But since September, they have started to creep up and over the last three weeks or so, we are now at more like 500 to 600 cases a day, so there's definitely an increase."
She said secondary school children made up the bulk of the cases, but there were signs of an increase in the 35 to 50 age group - potentially the parents of those children.
Dr Smith said there were not yet signs of an increase in the generation beyond that in Norfolk, but that some parts of the country had seen that happening.
She said, of people being tested, more were testing positive, which was an indication the virus is spreading in the community.
Dr Smith said people could help stem the spread by getting vaccinated, with a "significant" number of adults who have not had both doses.
The government has announced that children will be able to go to vaccination centres over the half-term week and Dr Smith urged parents to talk to their children about doing so.
She said early data was "reassuring" in that there is no evidence of more complications from children having the vaccination than there is from being infected with Covid-19.
And she said: "There are things people can do to protect themselves. I'm seeing fewer people using hand sanitiser, but I'd urge people to make sure they do.
"Carrying alcohol gel or sanitiser and washing their hands whenever they enter a new place, including their home, can help."
Dr Smith said the number of people who have tested positive for Covid-19 being treated in the county's hospitals has started to rise.
She said: "That figure was at about 100 at the start of September, but it came down to about 50. But at the moment it has increased to 72.
"That increase has happened over the past 10 days or so and that is a little bit of a concern."
Dr Smith said: "I think everyone is hoping that we will see the impact of the vaccination of children over the next few weeks - and half-term is a natural break.
"But I think it is becoming clear that the numbers are going to keep rising. It's a matter of how fast and how high."
Despite acknowledging the rising coronavirus case rates, Downing Street said a meeting of the cabinet did not discuss rolling out Plan B of the plan to control the virus this winter.
An official spokesman for prime minister Boris Johnson said: "No ... It remains the case we would only look to use that if the pressure on the NHS was looking to become unsustainable."
Dr Smith said: "The patterns are not the same as before because of increased immunity.
"There's not a single threshold where it becomes black and white that a decision over bringing in extra restrictions needs to be made.
"But I think in public health circles there is a quite a high level of concern that numbers are going to get higher and we are going to see more coronavirus through the winter."
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