A group of leading scientists have said it is too early to reopen schools in England on June 1.
The committee also said the later reopening date would give the government more time to develop and implement a "test, trace and isolate" programme, which has been touted as vital to the UK's lockdown exit strategy.
Boris Johnson has previously stated he aims to get reception, Year 1 and Year 6 pupils to return to primary schools from June 1.
The official Sage group, chaired by Sir Patrick Vallance, will publish advice on Friday on the safety of reopening primary schools.
The Independent Sage committee, chaired by the former chief scientific adviser Sir David King, is a newly formed group not to be confused with Sage which advises the government.
The plan to reopen schools has been a hotly debated topic across the country, with some local councils in England urging the government to reconsider its proposal.
Some council leaders said it was too soon for schools to reopen and that it risked the rate of infection increasing again.
Education Secretary Gavin Williamson has promised that scientific evidence in favour of reopening schools will be published shortly to ease fears from parents and school staff.
Schools in Scotland, Wales and Northern Ireland are not included in the plan.
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