June 7 (Reuters) - Carnival Corp will restart its namesake cruise line trips from U.S. ports this summer for fully vaccinated guests, the company said on Monday.

Peer Norwegian Cruise Line Holdings Ltd also said it would add more trips from multiple U.S. ports, including starting a trip from the West Coast.

Carnival said it would require guests to have received the COVID-19 vaccine 14 days prior to the cruise and have proof of vaccination. Norwegian Cruise said initial trips would operate with fully vaccinated guests and crew.

Cruise operators are among the last to return to their pre-pandemic operations as the U.S Centers for Disease Control and Prevention (CDC) laid out guidance earlier this year to the cruise industry for resuming trips, but did not set a date for resuming cruises.

The CDC said last month it had approved one cruise ship from Royal Caribbean to resume sailing in June.

Shares of all the three companies were up more than 1% in early trading. (Reporting by Nivedita Balu in Bengaluru; Editing by Shounak Dasgupta)