Watch a report for ITV News Anglia by Natalie Gray.
Schools facing the spread of the Omicron variant said they have lost up to a quarter of their teaching staff to sickness, as a senior MP called for the government to bring retired teachers back to the classroom.
The MP for Harlow Robert Halfon - the chair of the education select committee - wants the school system to be treated with the same urgency as the NHS, where doctors and nurses were urged to come back to help with the national effort.
He also warned that the country was moving toward school closures in the new year if urgent action was not taken.
His intervention came as schools told ITV News they were concerned about how they would deal with rising cases of the Omicron variant, with some questioning whether end-of-year exams might be at risk.
Mr Halfon addressed the House of Commons asking ministers to put measures in place to prevent schools from closing due to staff sickness.
He said: "What assessment is being made at the impact of loss learning for students in critical exam years? There's a nationwide campaign for an army of NHS volunteers but not for education.
"Why is a similar army of retired teachers and Ofsted inspectors not being recruited to support schools struggling to cope with staffing requirements?"
Several schools in the East of England have had to revert to online learning and even consider postponing exams, as the number of people testing positive for coronavirus increases.
City Academy in Norwich has a quarter of all teaching staff off sick, so has had to move lessons online for most pupils.
Headteacher Paul Collin said there was pressure on schools and the supply of agency staff.
"Locally that has been an issue for lots of schools, and making sure that we can provide a safe environment for young people where we've got enough staff supervising the classroom. It's meant that we'd have to move to some of those online learning."
At St Benedict's School in Bury St Edmunds, a number of end-of-term activities have been affected.
Headteacher Imogen Senior said: "We haven't been able to run a carol service, and we haven't been able to have carol singing in school in our assemblies because I think it doesn't feel like the right thing to be doing right now.
"Although we wouldn't be having traditional primary school type activities and celebration, we do often have things in school where we come together as a school community."
A union has warned that schools across the county are seeing "very severe low attendance" among pupils and teachers ahead of the Christmas break as the Omicron variant spreads.
Geoff Barton, general secretary of the Association of School and College Leaders (ASCL), said one school he knew had had around 25% of its staff off for three weeks amid Covid-19.
Mr Barton told ITV News Anglia: "We've got 236,000 young people across England not in schools. But the interesting thing is that it is wildly different in school A from school B.
"And similarly, you've got the issue that in some schools, you haven't got many teachers. So for example, as a school, I know 30 members of staff are off in the school across the road.
"But at another school it's pretty much business as usual, and that's what makes it so unnerving."
The NASUWT teaching union has called on the government to stagger the return of pupils to schools in January - and to publish guidance advising schools and colleges to cancel or postpone non-essential activities and events before Christmas - amid the spread of the Omicron variant.
The union added that guidance should make clear the actions that schools can take when dealing with "compromised" staffing levels - including sending pupils home where education cannot go ahead safely.
However, Downing Street has said schools should not be closing early for Christmas unless they have been told it is "necessary" on public health grounds.
The prime minister's official spokesman indicated that schools would be kept open unless there is an "absolute public health emergency".