(McClatchy-Tribune Information Services) -- Federal officials released new guidelines for schools today that reduced the time recommended for students to stay home after showing symptoms of the swine flu and other flu-like illnesses.

The recommendation was reduced from seven days after symptoms appear to 24 hours after the fever is gone.

Decisions on whether to close a school because of an outbreak of the H1N1 virus, or swine flu, will be left to local officials, but federal officials are recommending a school be closed only if it has a large base of students who are medically fragile or pregnant.

Other situations that could warrant a school closing is if there is such a large outbreak that it's administratively unwise for a school to stay open, or if parents are continuing to send sick children to school despite requests to keep children with fevers at home.

"There are relatively rare times when it makes sense to close a school just because the virus is present," said Dr. Thomas Frieden, director of the Centers for Disease Control and Prevention in a press conference this morning.

In crafting the guidelines, Frieden said federal officials weighed the benefits of limiting spread of H1N1 for a temporary period with the costs of the loss of education time for students, the increase in children being unsupervised and parents needing to take time off from work.

Currently, the virus is relatively mild when compared to seasonal flu, but if it should mutate to a more dangerous form, schools may have to consider screening children for illnesses, asking children with underlying health problems to stay home and increasing "social distances" in schools, such as making students sit further apart. Those aren't part of the current recommendations, but Frieden said schools and governments will have to be flexible because viruses can change quickly.

Vaccine against H1N1 is expected in October, and will likely be in two doses. Decisions will be made by state and local officials about where and how vaccines should be distributed, but schools will be one option.

Frieden said planning should occur now about how consent forms will be distributed and how school health officials will communicate with students' doctors about administering the flu vaccine.

Copyright (C) 2009, The Virginian-Pilot, Norfolk, Va.