WASHINGTON D.C.: The U.S. Centers for Disease Control and Prevention has recommended that only fully vaccinated people be allowed to board cruise ships departing from U.S. ports when sailings resume on July 11.

The CDC also recommended that cruise passengers be tested for Covid 1 to 3 days before their cruises and 3 to 5 days after their trips.

The CDC updates come after two passengers on Royal Caribbean Group's Celebrity Millennium tested positive for Covid, and new infections among crew members forced the delay of the first sailing of the Odyssey of the Seas.

"Since the virus spreads more easily between people in close quarters aboard ships, the chance of getting COVID-19 on cruise ships is high. It is especially important that people who are not fully vaccinated... avoid travel on cruise ships, including river cruises," the CDC said in a statement.

Last year, the CDC urged the public to stop traveling by cruise ships after incidents of the Covid infection spread quickly through ships.

The cruise industry has joined with the CDC to develop procedures to allow the restart of U.S. cruises.

However, cruise ships departing from U.S. ports report enormous losses and heavy debts after cruising came to a standstill during the pandemic.

As nearly half of the U.S population has been fully vaccinated, sailings on cruise ships are in high demand, according to industry observers.

On Thursday, Carnival lines said it has scheduled departures from Los Angeles, San Francisco and Ft. Lauderdale beginning in September.

Besides strong bookings in the cruise industry, ticket prices have increased, encouraging members of the cruise industry.