The Holland America Line’s Koningsdam was denied a stop in Puerto Vallarta, as the ship had reported that 21 crew members tested positive for Covid-19 after visiting Cabo San Lucas and Mazatlán. Since the cruise lines already have comprehensive protections in place, including vaccination and testing requirements designed to avoid allowing COVID-19 onboard, the Center for Disease Control and Prevention (CDC) has begun investigations into the sudden rash of cruise-ship cases.