More than 150 pupils and staff fell ill at Thorpe Willoughby primary school, near Selby.

Public health officials closed the school in an attempt to eradicate the bug.

Now headteacher Alan Dibb says pupils can return - but only if they follow medical advice.

Serious risk

Environmental health officials from Selby District Council collected samples from the school after it was forced to close on 24 May.

Mr Dibb said: "The important message that must go out to everybody is that children should only come back to school if they have been clear of symptoms for a full 48-hours.

"If we don't adhere to this then there is a serious risk of re-infection.

"That is the last thing we want, having gone through the last few days and having spent an awful lot of time and money getting the place thoroughly disinfected."

The health alert was sparked when youngsters began feeling sick and vomiting.