This is page 6 of their booking conditions:
If you test positive for COVID-19 within five (5) days prior to embarkation, you may elect to cancel your Booking. In that event, you, and anyone else in your travelling party who cancels their Booking due to your positive COVID-19 test result, will be entitled to a refund or future cruise credit equal in value to the amount Passenger paid to the Carrier. To qualify for the future cruise credit or refund, you must notify the Company via telephone at 877-665-4655 within twenty-four (24) hours of receiving the test result and no later than noon on the date of embarkation and provide verification satisfactory to the Company of test results administered by providers other than those retained by the Carrier. Under no circumstances shall the Carrier be liable to any such Passenger for any costs, damages or expenses whatsoever incurred by any Passenger.