Cruise ships can prepare to set sail again beginning Sunday under a conditional order issued by U.S. health officials that aims to mitigate the risk of Covid-19 transmission at sea by requiring a host of measures, including testing and quarantine, all designed to keep crews and passengers safe.

No ship will set sail with passengers immediately, and the cruise tourism industry may not rebound anytime soon. Under new guidelines issued by the Centers for Disease Control and Prevention on Friday, companies must be certified to sail by proving they can operate safely with crews onboard. To do so, they must carry out a simulated journey, or a number of simulated journeys, with unpaid guest volunteers or crew members playing the role of passengers.

The simulated journeys must provide regular onboard activities such as meal service and entertainment in common areas of the ship, while providing enough space for social distancing. Ships will be required to have laboratory capacity to ensure that routine testing for the coronavirus can be carried out at regular intervals, as well as when anyone embarked or disembarked from the vessel. Both crew members and passengers will wear masks in public spaces.