Burton Borough School on Audley Avenue in Newport was set to shut for operational reasons and instead take all lessons online.
A letter to parents from principal Krissi Carter yesterday said the decision was "not taken lightly".
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The letter said: "Due to a number of key staff having to self isolate, Burton Borough School will be closed for operational reasons as we will not be able to safely open the school.
"I would like to stress that this is not due to a public health need.
"All lessons will take place on Teams and resources will also be available there.
"Making the decision to close Burton Borough School has not been taken lightly and I would like to apologise for any inconvenience caused.
"Thank you for your understanding during these unprecedented times."
Parents are being asked to stay in touch with the school via email and social media platforms for updates about the school's opening.