Parents of Walbottle Academy pupils have been warned that "a member of the school community" has tested positive for Covid-19.
Close contacts of the infected person have been told to self-isolate for a fortnight.
Parents received the news in a letter, signed by Principal Martin Wood, dated September 20.
The letter, published on the academy's website, states close contacts had been urged to self-isolate until October 5, while any pupil not identified as a close contact "can continue to attend the academy as normal".
"I understand you may be concerned that someone has tested positive for the virus at the academy," adds Mr Wood.
"Please be assured that we have acted on this information immediately upon receiving the news and we have followed advice from (the Department For Education) about what action to take.
"As the academy has been strictly observing the guidance on infection prevention and control, it is not necessary to close the whole academy at this stage as the risk of transmission has been reduced."
It is the latest in a growing number of North East schools to be hit by the virus, with several in Sunderland still partially closed following confirmed cases.
And Sacred Heart Catholic High School, in Fenham, recently confirmed that a Year 11 pupil had tested positive.
It comes as Britain was warned there could be 50,000 daily Covid-19 cases by the middle of October due to the surging infection rate.
