Boris Johnson is coming under increasing pressure from MPs to spell out when children will be back to school.

Pupils of all ages - apart from vulnerable children and those of critical workers - have not been in the classroom since the start of the Christmas holidays.

But after the prime minister said he hopes it would be safe to reopen schools by March 8 - not after the February half-term as originally intended - what is the data and concerns surrounding when they should reopen?

What was Boris Johnson's reason for delaying reopening schools?

He said children will not return to classrooms until the four most vulnerable groups have been vaccinated.

It is hoped they will be immunised by February 15 - it then takes three weeks to be properly protected, meaning schools could reopen from March 8 at the earliest.

He added that the government would set out plans in the week beginning February 22 for the "gradual and phased" route out of lockdown.

Eastern Daily Press: Pupils of all ages have been learning from home since the start of the Christmas holidays.Pupils of all ages have been learning from home since the start of the Christmas holidays. (Image: PA)

Will all pupils return to classrooms on March 8?

Public Health England chief schools investigator Shamez Ladhani said last week: “Schools should be the first setting to reopen when it is safe to do so, and we are carefully monitoring the data.”

He said there was a “strong case for primary schools to reopen once infection rates start falling and are sufficiently low to allow easing of national lockdown measures”.

Coronavirus testing of school staff and pupils is ramping up ahead of their potential reopening in March. Primary school teachers and support staff have already begun to self-administer lateral flow tests at home twice a week.

What are infection rates in schools?

The Office for National Statistics (ONS) started testing children and staff in some schools in November.

The latest data available found just 0.75pc of primary school-aged children (5 to 11) gave a positive result. A higher percentage of secondary school-aged children (12 to 18) tested positive - 1.48pc - but still a relatively low proportion.

Eastern Daily Press: Studies and school admission data shows a higher percentage of secondary school-aged have tested positive for coronavirus.Studies and school admission data shows a higher percentage of secondary school-aged have tested positive for coronavirus. (Image: PA)

PHE concluded that transmission in primary schools was “extremely low” during the autumn term.

Dr Ladhani said: “While there is still more research to be done, these results appear to show that the rate of infection among students and staff attending school closely mirrors what’s happening outside the school gates.”

Could it be safe for schools to reopen sooner?

Paul Hunter, professor of medicine at University of East Anglia's Norwich Medical School, said the rate of the fall in Covid-19 cases made him optimistic that pupils could be back to classrooms before the March 8 target date.

He said: “I think there could well be a case for opening schools sooner – I particularly think schools for children under 11 years of age, where the evidence that they contribute to the spread of the epidemic in the wider population is a lot lower.

Eastern Daily Press: Paul Hunter, from the University of East Anglia. Photo: UEAPaul Hunter, from the University of East Anglia. Photo: UEA (Image: Archant)

“I would certainly hope to see schools, and particularly junior schools, opening relatively soon, but headteachers need a couple of weeks to prepare for that.”

Could opening too soon lead to a surge in new cases?

Dr Deepti Gurdasani, a senior lecturer in epidemiology at Queen Mary University of London, said evidence suggested that primary children were twice as likely as adults to be the first case in a household.

She is urging the prime minister to resist pressure to reopen sooner.

“We are in a very, very precarious position. Parents and children have made huge sacrifices because of schools being closed to most children. It’s very important we don’t squander this,” she said.

Former Suffolk head Geoff Barton, general secretary of the ASCL head teachers' union, said: “Everybody wants to see all pupils back in school as soon as possible, but it is of critical importance that this happens when scientists believe it is safe to do so without triggering an immediate increase in infection rates and necessitating another period of restricted opening.”

Eastern Daily Press: Geoff Barton, general secretary of the Association of School and College Leaders, welcomed the change Picture: PHIL MORELYGeoff Barton, general secretary of the Association of School and College Leaders, welcomed the change Picture: PHIL MORELY (Image: Archant)

Could schools be forced to close again later this year?

With the roll out of the vaccine across the population and resulting reduction of infection rates, Prof Hunter said he also expects schools will have a full academic year next year with minimal interruptions, although local outbreaks could still occur.

He said: “I think it is unlikely that we will feel the need to close schools again during this pandemic but that is not a 100pc guaranteed certainty.”