Authorities in the eastern Caribbean island of St. Lucia have quarantined a cruise ship after discovering a confirmed case of measles aboard. Dr. Merlene Fredericks-James, the island's chief medical officer, said Thursday that the ship is still in port and that no one has been allowed to leave it.

"Whilst in our ports, we will continue to monitor and will not allow disembarkation, given the contagious nature of the disease," she said in a statement provided to CBS News, adding that the ship was free to leave St. Lucia if it chooses.

Fredericks-James identified the infected person as a female crew member who is in stable condition. She said the ship's doctor has requested 100 doses of the measles vaccine and that St. Lucia is providing them at no cost.

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The St. Lucia Health Ministry confirmed Thursday that the ship involved is the Freewinds. The 440-foot vessel reportedly belongs to the Church of Scientology. According to the church's website, the ship, which is normally docked in the Dutch Caribbean island of Curacao, "is the home of the Flag Ship Service Organization (FSSO), a religious retreat ministering the most advanced level of spiritual counseling in the Scientology religion."

An unidentified person who answered the phone at the church's media center said no one was immediately available for comment.

St. Lucia authorities did not provide any additional details about the person with measles, but Fredericks-James said in a statement that "the confirmed case, as well as other crew and passengers are stable and remain under surveillance" by the ship's doctor. She said continued medical surveillance will be necessary during the incubation period for measles, which ranges from 10 to 12 days before symptoms appear.

Measles is highly contagious and is spread through the air when an infected person coughs or sneezes. It is so contagious, in fact, that if one person has it, up to 90 percent of people near them who are not immune will also become infected.

Symptoms of measles include a high fever, runny nose, and a red-spotted rash. Most people recover, but measles can lead to serious complications including pneumonia, brain swelling and even death in some cases. "The disease can be particularly severe in young children who are not immunized," Fredericks-James noted.

Measles has sickened more than 700 people in 22 U.S. states so far this year — the largest number of cases in 25 years. Federal officials saying the resurgence is largely driven by misinformation about vaccines; unvaccinated people are vulnerable to the spread of the virus when cases are brought back from overseas.

In Fullerton, California, hundreds of movie goers at a showing of "Avengers: Endgame" were told they may've been exposed to measles last week by a woman who was infectious.