Nine schools in Birmingham and the Black Country remain closed following an outbreak of the Norovirus or winter sickness disease and flu virus.
Hundreds of children at schools in Shropshire and Staffordshire have also been affected by the illness.
Experts have said the number of children affected was broadly in line with a winter virus.
Symptoms suffered by those affected included vomiting, high fevers, diarrhoea and lethargy.
At its height on Wednesday 10 schools in the area were closed.
Birmingham City Council said six schools are still closed on Thursday.
BIRMINGHAM'S CLOSED SCHOOLS
Mansfield Green School, Aston
Matthew Boulton Community Primary, Handsworth
Hawthorn Primary, Kingstanding
Summerfield Primary, Winson Green
Benson Community Primary, Hockley
Perry Beeches Junior School, Great Barr
In the Black Country Moat Farm Infants School in Oldbury, Annie Lennards Infants and Uplands Manor Primary, both in Smethwick, were also closed on Wednesday and remained shut on Thursday.
Sandwell Hamstead Junior School, which had been closed on Tuesday and Wednesday with 120 pupils out of 270 affected, reopened on Thursday.
A spokesman for the council said: "Most children have been off school for between two to four days with only one child admitted to hospital.
"We are currently aware of around 30 schools in the Birmingham area that have reported high volumes of pupil absence due to sickness.
"However as this is not a notifiable infection, schools may not have contacted the Health Protection Unit."
Meanwhile in Staffordshire nearly 300 pupils at the Sir Graham Balfour School in Stafford have been off ill with the winter sickness bug and a further 200 have been affected at William Brookes School in Much Wenlock, Shropshire.
Parents are being urged to ensure their children are symptom free for at least 24 hours before returning to school.
Wolverhampton's New Cross Hospital is also asking anyone who has been in contact with people with the virus not to visit patients.