A pupil from Shrewsbury School has contracted bacterial meningitis.
The 15-year-old, who has not been named, was taken unconscious to hospital on Thursday morning.
The pupil, who is not a boarder at the private school and is said to live locally, regained consciousness on Friday morning, but remains in intensive care at the Royal Shrewsbury Hospital.
Other pupils who may have come into contact with the teenager are being offered antibiotic treatment along with his family.
The Health Protection Agency said the chances of catching meningitis were extremely small.
But they warned anyone who experiences suspicious symptoms to contact their GP or NHS Direct immediately.
Earlier this month the Meningitis Trust issued a warning to all students after 10 cases emerged at a variety of universities.