Doctor Sarah Harrison outlined the measures in place in Torbay
The principal of a Devon school where a pupil contracted swine flu said closing it was not an easy decision, but the health of pupils was "paramount".
The 12-year-old girl is currently being treated for the condition after returning from a holiday in Mexico.
Paignton Community College will remain shut until 11 May. Year seven students have been given anti-viral drugs.
Health officials said a small number of other local people were being tested after getting flu-like symptoms.
Principal Jane English said: "We don't take closing the school lightly, but the health and well-being of our young people and our staff is absolutely paramount.
"It's not an ideal time with young people taking public exams, but clearly health is far more important."
Chief Medical Officer Sir Liam Donaldson said only one school had been affected
She said the girl who had contracted swine flu was at home and not feeling very well, but was improving.
She had attended school last week before developing symptoms, but had not returned since Friday night when her parents called in health experts.
Three hundred and forty courses of anti-viral treatment have now been given to pupils and staff who requested them.
Dr Sarah Harrison, public health consultant for Torbay Care Trust, said: "We are aware of a small number of people who do have sort of flu-like symptoms that we are interested in.
"The sorts of numbers are more a dozen than hundreds."
She said cases were being dealt with on an individual basis at the health protection unit in Dartington.
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