Measles is a highly contagious disease caused by a virus that can spread through the air when an infected person coughs or sneezes or if someone comes into direct contact or shares germs by touching the same objects or surfaces.
No one is allowed to leave the ship, NBC reported, but the ship is allowed to leave St. Lucia.
The island has avoided an outbreak of the disease locally since 1990, the acting national epidemiologist, Dr Michelle Francois, said in another statement.
On Wednesday, the chief medical officer on the island of St. Lucia confirmed that the Ministry of Health was investigating a possible case of measles aboard a cruise ship now docked in one of its ports.
The vessel in question, named "Freewinds", is now moored outside the St. Lucia coast.
The ship is normally docked in the Dutch Caribbean island of Curacao and serves as a religious retreat, the church's website says.
The Church of Scientology has not officially published a stance on vaccines, and does not prevent followers from following doctors advice or taking medicine. "It is the most significant spiritual accomplishment of his lifetime and brings with it the full realization of his immortality", the website stated.
This developing story will be updated as more information becomes available.
Epidemiologists say that in order to stop the measles from spreading, 95 percent of people either need to have been vaccinated against it or developed an immunity from having already had it.
Saint Lucian authorities say they don't have the authority from leaving port. "They make their own decisions, but those aren't decisions that the church tries to influence in any way". But as The Hollywood Reporter notes, several high-profile Scientologists have spoken out against vaccination. Once unvaccinated communities are exposed, it becomes hard to stem the spread of measles. Quarantines were declared at the L.A. campuses of both schools, affecting hundreds of students and staff, unless they could show proof of vaccination.
Preliminary global data showed that reported cases of measles have been up almost 300% in the first three months of 2019 compared to the same time frame in 2018, according to the World Health Organization.