Friday Bridge Primary School was closed down yesterday after children became poorly.
Today Cambridgeshire County Council said half the school's 100 pupils had contracted the winter vomiting bug norovirus.
A number of staff members, including head teacher Jayne Williams, have also been taken ill.
The school will remain closed today. But the council said it was hoped that it would re-open after half term.
Norovirus is a common tummy bug, which causes stomach cramps, vomiting and diarrhoea.
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