The HSE is set to investigate an outbreak of human swine flu at a second school in Cavan.
At least one case of the virus has been confirmed at Breffni College secondary school, while 20 other students have flu-like symptoms.
The HSE says the school should remain open, but students with symptoms should stay at home.
Earlier this week, a swine flu outbreak was reported at Laragh National School in Cavan, with at least four children testing positive for the virus.