Schools across the United States are canceling trips abroad, preparing online lessons and even rethinking “perfect attendance” awards as they brace for the possibility that the new coronavirus could begin spreading in their communities.

Districts have been rushing to update emergency plans this week after federal officials warned that the virus, which started in China, is almost certain to begin spreading in the U.S. Many are preparing for possible school closures that could stretch weeks or longer, even as they work to tamp down panic among students, parents and teachers.

President Donald Trump has worked to minimize fears about the virus, but on Wednesday he and federal health officials recommended that schools start planning for arrival of the COVID-19 virus “just in case.”

“It’s the perfect time for businesses, health care systems, universities and schools to look at their pandemic preparedness plans, dust them off, and make sure that they’re ready,” Dr. Anne Schuchat, principal deputy director of the U.S. Centers for Disease Control and Prevention, said at a Wednesday news conference.

School letters sent home from Florida to California this week sought to assure parents that, in most communities, the risk of exposure to the virus is still very low. Most suggested the same precautions used to combat the flu: Wash hands frequently, cover sneezes and coughs, and stay home if fever or other symptoms arise.

At schools, cleaning crews have been told to pay extra attention to door knobs, keyboards and other surfaces that students touch through the day. Some districts have invested in handheld disinfectant sprayers that are used in hospitals, Others are adding traditional hand sanitizers in schools and buses.

But even as they work on prevention, schools are also starting to prepare for the worst. Many are making plans to teach students online in case the virus spreads so widely that schools are forced to close. Officials are considering how they would handle large numbers of absences among students or teachers, and how to make up days that could be missed because of the virus.

At least one school temporarily closed Thursday over fears tied to the virus. Bothell High School, near Seattle, canceled classes after a staffer’s family member was placed in quarantine for showing symptoms of possibly contracting the virus. Officials said the school was being cleaned and disinfected “out of an abundance of caution.”

In Miami, public school leaders said they’re readying 200,000 laptops and tablets for students in case buildings close and force classes online. They’re also directing new international students to register at two reception centers instead of at school buildings, where students have typically registered.