The U.S. Centers for Disease Control and Prevention (CDC) issued its first roadmap surrounding K-12 schools reopening as the country continues to fight the COVID-19 pandemic. The guideline centers on five mitigation strategies: universal and correct use of masks; physical distancing; hand-washing and respiratory etiquette; cleaning and maintaining healthy facilities; and contact tracing in combination with isolation and quarantine.

While it was added that each strategy is important, CDC recommends “prioritizing the first two”– wearing masks and physical distancing. Vaccines and testing are not among the “key” strategies the agency lays out, calling them “additional layers” of COVID-19 prevention. The new recommendations come amid a national debate about when and how to reopen schools, even as fear of spreading the coronavirus continues and a push to prioritize teachers for vaccinations grows.

“I want to be clear, with this operational strategy, CDC is not mandating that schools reopen. These recommendations simply provide schools a long-needed roadmap for how to do so safely under different levels of disease in the community,” said CDC Director Dr. Rochelle Walensky in a news briefing on Friday.

The CDC recommendations include a color-coded chart to describe levels of transmission from blue for low transmission, to yellow for moderate, to orange for substantial and then to red for high transmission. According to the CDC website, for every 5 additional cases per 100,000 population in regional incidence, the risk of a school outbreak increased by 72%. The release of the 35-page CDC report comes as many public schools, more than half, according to some estimations, have already reopened, while others, particularly in cities, remain closed. The CDC acknowledged that many of the schools operating in-person are doing so safely.