Boris Johnson has insisted schools are safe but also said they increase the spread of COVID-19.
The prime minister said schools were safe during a Downing Street press conference on Wednesday.
He said: “The problem is not that schools are unsafe – teachers and headteachers have worked heroically to make sure they are safe, they are COVID-secure.
“The problem is that by definition schools bring many households together and that contributes to the spread of the virus within the community and drives up the R.”
The news confirms hopes of pupils returning to class after the February half-term have been abandoned, as the PM said the battle with coronavirus remained “perilous”.
Deputy chief medical officer Jonathan Van-Tam also responded to a question on how schools can be both safe places to be and vectors of transmission.
He said children with COVID-19 were more likely to transmit the virus if they were in “upper teenage years”.
But he said it wasn’t clear if teachers mainly picked up the virus from pupils or each other, and also suggested they could pick up the infection in their own lives outside of school.
He added that there wasn’t a clear signal in the data of a markedly increased rate of infection or mortality in teachers, but did stress that infected children could introduce the infection back in their own household and therefore contribute to an increase in R.
Speaking in the House of Commons on Wednesday, the PM said schools won’t reopen and “other economic and social restrictions” won’t be eased until at least 8 March.
Johnson told MPs: “If we achieve our target of vaccinating everyone in the four most vulnerable groups with their first dose by 15 February, and every passing day sees more progress towards that goal, then those groups [will] have developed immunity from the virus about three weeks later, that is by 8 March.
“We hope it will therefore be safe to begin the reopening of schools from Monday, 8 March.
“With other economic and social restrictions being removed thereafter as and when the data permits… then or thereafter I should say.”
The date happens to be a target set by a group of lockdown-sceptic Conservative MPs for Johnson to start easing the current lockdown.
Johnson revealed that his government would set out a roadmap for lifting lockdown in the week beginning 22 February, with schools opening no earlier than two weeks later.
The announcement amounts to an extension of England’s national lockdown by another three weeks.
On Monday, it was suggested Johnson wanted to start easing restrictions – including reopening schools – on 15 February.
Watch: What you can and can't do during England's third national lockdown