(HealthDay)—Cruise ships can resume sailing in U.S. waters as long as 98 percent of crew and 95 percent of customers are vaccinated against COVID-19, the U.S. Centers for Disease Control and Prevention says.

Companies that meet the stipulation will be allowed to return to U.S. waters by midsummer, the CDC said in a letter to cruise lines on Wednesday, CBS News reported. The agency also eased some previous testing and quarantine requirements for .

Major cruise lines stopped sailing from U.S. ports in March of last year after the CDC issued a "no-sail" edict due to the COVID-19 pandemic. Last week, Alaska joined Florida in suing to overturn the CDC mandate against immediate resumption of cruises in the United States, CBS News reported. On Thursday, Royal Caribbean CEO Richard Fain referenced the CDC letter in an earnings call, saying the company now foresees sailing from the United States again during the Alaska cruise season, roughly May to September.

Cruise ships are often settings for disease outbreaks because of their closed environment and close contact between travelers from many countries, according to the CDC. Then the novel coronavirus emerged. From Feb. 3, 2020, to March 13, 2020, there were roughly 200 cases of COVID-19 confirmed among returned cruise travelers from multiple ocean voyages, including Carnival Cruise Lines Diamond Princess and Grand Princess, according to the CDC.

The Diamond Princess and Grand Princess had more than 800 COVID-19 cases, including 10 deaths, the CDC said last year, CBS News reported.

More information: CBS News Article