Norfolk cases of coronavirus caused by the South African variant of Covid-19 are being "watched like hawks", the county's public health director has said.
Dr Louise Smith said there were between five to 10 cases of Covid-19 which had been identified as being the South African variant.
That number is up from the three which had been identified in the middle of January.
There are concerns that a mutation in that variant makes it more contagious.
The government has ordered targeted testing in eight other areas of the country where cases of it could not be linked to travel to or from South Africa.
Dr Smith said all the cases in Norfolk were linked to travel, but she said: "We are watching this like hawks.
"We still have very low case numbers, between five to 10 cases.
"But what we have done is adopted a more hands-on approach to contact tracing.
"That's being done by a specialist consultant in public health, with more bespoke advice and more support.
"So, we've set let us arrange deliveries to those people and, if a friend had been doing them, then get them tested as well.
"We are confident at this stage that everybody who has been sequenced and found to have the South African virus has a link to travel to South Africa, either themselves or because someone in their household has travelled."
Coronavirus in numbers: UK death toll at 109,335
'Cautiously optimistic'
Dr Smith said she was "cautiously optimistic" over the falling numbers of coronavirus cases in Norfolk - as the roll-out of the vaccine continues.
The rate of Covid-19 cases in Norfolk is now below 300 per 100,000 people, although Norwich and Great Yarmouth, while falling, remain in the top 75 areas of the country in terms of positive tests.
Dr Smith said: "The number of cases in Norfolk are definitely going down and that is a reason to be positive, as has the fact our local NHS has vaccinated hundreds of thousands of people.
"We are going to head into better weather, so I'm cautiously optimistic, but it is going to take some time for numbers to come down - that will happen much more slowly than the rate in which they went up.
"We saw an increase which was really rapid and the speed with which it will come down will be much, much slower.
"We saw a 100pc rise over seven days, but the fall is likely to be closer to 20pc over each seven days."
She said she thought Norfolk had been hit a bit later than some areas in this wave, so the cases would now take longer to fall than some parts of the East of England.
Prof Andrew Hayward, from the Scientific Advisory Group for Emergencies (Sage) had said there would be a "phased opening up" as vaccination levels increase and things would be "more or less back to normal for the summer".
And Dr Smith said: "If you look back to the pattern of what we saw last year and what we know about the virus, it is reasonable to anticipate that numbers will be very, very low in the summer.
"And, on top of that, it's reasonable to expect the vaccine will have an impact. What we are all looking at is to see the impact of that on the numbers being admitted to hospital."
There are currently 575 patients who have tested positive for Covid-19 in the county's hospitals.
Care homes
Recent weeks have seen record numbers of deaths in Norfolk's care homes, with more than 100 in the past week.
There are currently 167 Covid outbreaks - where two or more people have the virus linked to one setting - within care homes.
But Dr Smith said analysis of the rate of deaths per care bed did not suggest Norfolk was an outlier in that regard, but in line with other areas.
However, she said, with Norfolk peaking slightly later than other areas, that was reflected in the statistics for recent care home deaths.
Dr Smith said Norfolk's care homes had also not been affected as much as might have been expected in the first wave last year.
And she said: "I am confident that the number of outbreaks is now coming down."
She said residents in all but about 12 Norfolk care homes had now received vaccines.
Dr Smith said that dates had been fixed for those yet to have jabs to be administered.
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