People need to follow tough new rules carefully to prevent spread of the highly infectious variant of coronavirus, Northern Ireland’s chief scientific adviser has warned.

A spike in hospital admissions is not expected to peak until the final two weeks of January, Professor Ian Young added, after Stormont ministers significantly tightened social mixing restrictions.

He attributed the rise mainly to increased socialising before fresh lockdown measures were brought in after Christmas rather than the virus mutation prevalent in southern England.

Prof Young said: “The existing mitigations need to be adhered to particularly carefully to reduce transmission of the virus.”

The reproductive rate of the virus is approaching 1.8 and hospitals are at full capacity.

Belfast’s Nightingale hospital is being expanded.

Prof Young added: “It is likely that hospital admissions and numbers of patients requiring hospital treatment will continue to rise.”

He defended the decision to increase the time between the first and second doses of the vaccine.

Prof Young said: “Having reviewed the evidence myself, I am content that the decision that has been made is in the best interests of our population as a whole.”

Covid-19 would probably always be with us and repeated rounds of vaccination were likely to be needed, the top official advising ministers on the science and modelling of the disease said.

Prof Young told Stormont’s health committee that at the moment, he is not concerned about resistance to the vaccine from the mutations they know about.

He said “structural” changes to the virus were of more concern as they were more likely to develop resistance to vaccination.

There was more uncertainty about the South African variant as there were greater levels of structural changes within that, he added.

Strict new measures including a legally enforceable stay-at-home order have been agreed by Stormont ministers.

Schools will move to remote learning until well into February.

There is debate over school transfer tests after one exam provider cancelled its testing process while another moved its test to next month.

GCSE exams will go ahead next week unless the education minister cancels them.

Ministers agreed on Tuesday to give police the power to enforce the stay-at-home order, taking effect from Friday.

Northern Ireland’s Police Federation expressed concern about “gaps” in that law.

Household mixing will be reduced to just one other household or social bubble.

There are also additional restrictions to household mixing.

So in private homes and gardens, both indoor and outdoor gatherings will be restricted to members of one household, or a member of your support bubble.