Hundreds of children missed class on Monday as 11 Bradford schools remained closed by a winter vomiting bug.
Schools are being deep-cleaned to try to beat the bug
The schools shut on Friday as infection teams deep-cleaned their buildings in a bid to stamp out the bug.
Staff and pupils across the city have been affected by the bug which causes vomiting, high fevers and diarrhoea.
Anthony Mugan from Bradford's Education Department said he had also advised mosques and madrasas to restrict activities such as community events.
He said the bug could still be around for some time yet.
Parents have been told that if their children have symptoms of sickness or diarrhoea they should not attend any community activities until they have been well for at least 48 hours.
Mr Mugan said: "Challenge College, Hanson School and Laisterdyke Business and Enterprise College and eight primary schools will be given a deep clean to try to stop the virus spreading further.
"We are using a co-ordinated approach to try to stamp out this bug in this area where the number of instances has risen and the whole community is affected.
"The virus is not originating in schools and schools have been taking all the precautions they can to stop it from spreading."
Primary schools closed on Monday will be Green Lane, Frizinghall, Heaton St Barnabas, Lilycroft, Thornbury, Lapage, Bradford Moor and Killinghall.
Lilycroft and Midland Road nurseries will also be closed, and Abbey Green nursery will be partially closed on Monday.
He said it hoped to reopen all the buildings on Tuesday.