But with 1,100 probable and confirmed cases and two deaths in the United States - and projections that those figures will swell - closing schools isn't effective.
"We know that in communities that are seeing cases in the school, they're already seeing cases in the communities," said Besser. "So a strategy of trying to stop the transmission by approaching it as a school phenomenon is not very appropriate."
Besser acknowledged the hardship schools and parents face when schools close suddenly and said officials weighed those worries against public health concerns when revising their recommendations.
"When we hear of the difficulty involved of children who are dropped at libraries because there's nowhere for home care, of people who could lose their jobs because they don't have sick leave, these factors are really real," he said.
There have been no deaths in Maryland and no hospitalizations. Nationwide, the virus appears no more serious than a seasonal flu, which would not normally close schools.
In addition to Rockville High, the schools that will reopen today are: Milford Mill Academy in Baltimore County, Folger McKinsey Elementary in Anne Arundel County, and Montpelier, University Park and Vansville elementaries in Prince George's County.
