Schools in England are to close from Friday for all pupils – except for vulnerable students, and those with key worker parents.
Education secretary Gavin Williamson told the Commons that the balance of risk had changed, and schools were struggling to stay open.
Key workers include NHS staff, the police and delivery drivers.
At a press conference Boris Johnson said “exams will not take place as planned in May and June” – but the government will make sure children get the qualifications they need.
The Prime Minister also advised parents that children should not be left with older grandparents.