Reports of Covid-19 outbreaks on dozens of ships have dampened investor enthusiasm for the three big US-listed cruise lines.

After adding $2bn in market capitalisation in a single day on 21 December following Carnival Corp's upbeat outlook for 2022, reports of outbreaks on more than 90 ships appear to have kept shares from rising any further.

By Thursday, the US Centers for Disease Control (CDC) said there were reported cases of Covid-19 on 34 Carnival ships, 41 Royal Caribbean Group vessels and 16 Norwegian Cruise Line Holdings ships.

In New York, shares for Carnival, Norwegian, and Royal Caribbean started Thursday at roughly the same place as they did after last week's New Year outlook rally.

Carnival, which closed at $20.54 on 21 December, opened down $0.24 at $20.66 after spiking to a high of $21.67 on 28 December.

Norwegian slid $0.45 in early trading to $21.45, below the 21 December close of $22.19.

The company's shares continued to rise following the rally but cooled off beginning on Tuesday.

Royal Caribbean shares lost $1.02 early, falling to $77.23. It closed at $76.57 on 21 December.

All three cruise lines have ships among the 86 currently under investigation or observation by the CDC.

Over the weekend, cruise ships were reportedly returning to Florida after outbreaks on board among both passengers and crew.

As the week wore on, the numbers swelled for both the cruise majors and smaller players, such as MSC Cruises, which has outbreaks on two ships, and the Walt Disney Co, which has outbreaks on four.

As 2021 closed, Carnival, Norwegian and Royal Caribbean all said they were expecting 2022 to be strong following two difficult years brought on by the pandemic.

Norwegian said it would be back to full capacity by April 2022, while Royal Caribbean said it expects a full-year profit and Carnival reported $1.29bn in revenue for its fourth quarter, which ended on 30 November.

Carnival, which reported results last week, said it would be profitable in the second half of the year.