The Education Secretary has admitted to planning for a quarter of school staff being off with Covid as he warned absences would increase this week.
Nadhim Zahawi said staff absenteeism was around 8.5% last week as schools began to reopen after Christmas, up from 8% at the end of last term.
But he warned that numbers "will increase, no doubt, because obviously now schools are back we're going to see an increase in infection rates".
Ministers are making contingency plans for rising numbers of staff being off with some schools facing absences of up 40% but still keeping their doors open.
"We have to make plans for every outcome, that's the responsible thing to do," Mr Zahawi told BBC Sunday Morning.
"I have to have contingency plans for 10, 15, 20, 25% absenteeism because obviously Omicron is far more infectious."
He said the vaccine rollout for 12 to 15-year-olds needed to go "much faster" after the Government missed its target to jab the majority of younger teens by the October half term.
Only around half of this age group have had the jab, Mr Zahawi said.
"We have to go much, much faster which is why we are going back into schools on Monday with the school age vaccination programme," he said.
The Cabinet Minister said Covid would eventually become "endemic" and people would live with the virus.
But he added: "The next two weeks will be bumpy as staff absenteeism will rise as students go back into education.
"On the whole, this has been a good start last week. This week will be important."
He also backed calls for the Covid self-isolation period to be cut to five days if experts deem it safe, in order to ease staff shortages.
It comes are grim warnings from heads that schools are "teetering on the edge" with more than a third reporting staff absence levels of over 10% due to Covid on the first day of term.
The poll of nearly 2,000 school leaders in England by the NAHT union came amid mounting fears over fresh disruption to children's learning.
The snap survey found the majority (95%) of heads had pupils absent due to Covid, while nearly a third (29%) reported over 10% of children were out of class because of the virus.
Paul Whiteman, general secretary of NAHT, said: “Schools are doing everything they can to maintain education for pupils in the face of very challenging circumstances.
"Staff absence on the first day of term was considerable and could very likely rise as the term progresses.”
Mr Zahawi also insisted that exams would go ahead this summer, with more details to come next month on the measures needed to make assessments fair for pupils.
He said: "My absolute commitment is that exams are going ahead both this January and for the summer, for GCSEs and A-levels, but we're putting in mitigations to make sure that we recognise who have had their education disruption."
