The decision to cancel classes Monday in at least a dozen schools in the greater Seattle area indicates how essential it is for school districts to have contingency plans and could be a preview for communities across the country weighing what preventative steps to take, health experts say.

In Mill Creek, Washington, a high school has decided to close after officials announced Friday that a student had somehow contracted the disease known as COVID-19. In addition, an elementary school in Lake Oswego, Oregon, south of Portland, is shutting its doors through Thursday after a person who lives with a school employee tested positive for the disease.

Health experts, however, are advising caution for school officials who must balance making safety and cleanliness a top priority at schools while being mindful not to make unnecessary closings at a time when COVID-19 is not considered a risk to the larger U.S. student population. But experts added that now is the time to prepare a contingency plan.