Northern Ireland's chief scientific officer has said it will be very difficult to keep schools open if the new variant of Covid-19 becomes dominant there.

The first positive case of the new strain in Northern Ireland was confirmed yesterday.

"If the variant were the dominant form in Northern Ireland, then it is very unlikely that we could keep R at less than 1 and schools open," Professor Ian Young told BBC Radio Ulster's Stephen Nolan programme.

He said he does not believe that at present the variant is a "major form" in Northern Ireland, but said he is confident there is a small number of cases.

The Stormont Executive issued guidance earlier this week in response to the emergence of the variant, which recommends against any non-essential travel between Northern Ireland and both Britain and south of the border.

The executive also agreed to advise anyone arriving in Northern Ireland, who is staying for more than 24 hours, to isolate for 10 days. It applies to anyone who has arrived since 22 December.

"This particular variant does appear to be significantly different than many of the others which have been in circulation, it has a number of different mutations or changes to its genetic material and those affect the structure of some of the key parts of the virus.

"As a result it is highly likely that the virus is transmitted more easily than the form of the virus that we have been used to, somewhere between 40-70% more easily transmitted," he said.

"We don't think it causes a more severe disease... and we are reasonably confident that it will still respond to the vaccine and that the vaccine will protect against this variant form."  

There have been 841 cases of Covid-19 reported by the Department of Health in Northern Ireland today.

Eleven people who tested positive for the coronavirus have also died.

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Professor Young said he is "very concerned" about the new variant form of the virus because it is transmitted more easily.

"The impact of that, if it became established in Northern Ireland, for example at the moment R is probably sitting between 1 and 1.2, and if we had the variant form and we were all behaving in the same way, R would be closer to 1.6 and 1.8, and that would have severe consequences," he said.

He said there would likely be stronger restrictions for longer if the variant form of the virus became the dominant strain.

Meanwhile, Northern Ireland is set to enter a new lockdown on St Stephen's Day, of which the first week will be the toughest so far imposed in the region.

A stay-at-home curfew will be in place from 8pm to 6am for that week.

Professor Young urged the public to adhere to the restrictions.

"At the moment I think it is only circulating in fairly small amounts, and what we can do to prevent it becoming the dominant strain is for everybody in the next six weeks to adhere really strictly to the mitigations and restrictions that are in place," he said.

"That gives us the best opportunity of preventing this variant form from becoming established until vaccination begins to take significant effect in our population."

Northern Ireland's Deputy First Minister Michelle O'Neill has urged the public to follow new lockdown regulations which start from 26 December.

"We were advised that this variant is likely to have been present here for some time," she said.

"Unfortunately this is the confirmation we have been expecting and that's why it is critical we all get the maximum benefit from the lockdown that starts on St Stephen's Day.

"There is no current evidence to suggest that this current variant of Covid causes more serious illness or a higher mortality rate or that it affects vaccines and treatments. Vaccines have already started rolling out to those healthcare staff working on the front line and to residents in our care homes.

"My appeal is for everyone to strictly follow the Covid regulations and the public health advice and be very careful in all that we do over the Christmas period."