In a letter sent to affected guests today, Carnival Cruise Line informed them that, unfortunately, their upcoming cruises aboard Carnival Horizon had been canceled. The cancellation also affected extended to the currently underway cruise, which had to skip two ports of call for the ship to return to her homeport. The two upcoming sailings and currently underway cruise aboard the Carnival Horizon have been canceled due to an issue affecting the ship’s maximum cruising speed.
UPDATE: Carnival Cruise Line has provided an update on the ships state of repairs

Carnival Horizon Cruises Cancelled
Carnival Cruise Line has canceled the December 5 and December 11 cruises on Carnival Horizon scheduled to depart from Miami, Florida. In a letter sent to affected passengers, the cruise line said that the ship is experiencing an issue with the maximum cruising speed and will be forced to cancel the two upcoming cruises.
It is an issue that has impacted Carnival cruise ships over the years, with Carnival Horizon becoming the latest to experience the problem. The last Carnival cruise ship to experience issues with its maximum cruising speed is its sister ship, Carnival Panorama, in August 2021. And in 2019, Carnival Dream and sister ship Carnival Vista experienced similar issues.
At the time of this writing, no other Carnival Horizon cruises have been canceled or altered.
Guests Impacted by the Cancellation

Passengers booked on the canceled cruises will receive a full refund and a 100% future cruise credit (FCC), based on the value of the fare, that can be applied towards a future Carnival cruise. Guests must redeem the credit by November 30, 2022.
Carnival Cruise Line will automatically process refunds for guests. The refund will include a 100% refund for cruise fares, taxes, port fees, pre-paid gratuities, Wi-Fi packages, shore excursions, beverage packages, etc.
The cruise line will also reimburse guests up to $200 per person on any independent, non-refundable air expenses/change fees. In addition, passengers who made a reservation for an in-terminal antigen test on the day of sailing will have the payment refunded.
Carnival sent a letter to guests who were booked for the cruises with complete details regarding refunds. The cruise line also apologized for the cancellation and stated they hope to welcome passengers back on a future Carnival cruise.
In the letter, Carnival said, “We sincerely apologize for the unanticipated disruption to your vacation plans. We are very disappointed that we have to cancel your cruise with such short notice.“
Carnival Horizon is currently sailing six to eight-night cruises to the Caribbean and Bahamas from Port Miami.