American cruise lines may be able to set sail from U.S. ports this summer, according to a letter sent to the cruise industry by the Centers for Disease Control and Prevention (CDC).

In a letter obtained by USA Today, the CDC said cruise ships may be able to sail by mid-July if at least 98% of the crew and 95% of passengers are fully vaccinated against COVID-19.

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If a cruise line does not want to wait for that percentage of crew and passengers to get vaccinated, it may apply for a simulated voyage, which allows the crew to practice COVID-19 procedures with volunteers, and get a response from the CDC within 5 days, rather than the previously expected 60, meaning ships could set sail much faster.

"We acknowledge that cruising will never be a zero-risk activity and that the goal of the [Conditional Sailing Order's] phased approach is to resume passenger operations in a way that mitigates the risk of COVID-19 transmission onboard cruise ships and across port communities," Aimee Treffiletti, CDC's head of the Maritime Unit, said in the letter.

In a statement about the CDC's letter, the CEO of Royal Caribbean Group, Richard D. Fain, said "although this is only part of a very complex process, it encourages us that we now see a pathway to a healthy and achievable return to service, hopefully in time for an Alaskan season."