Adina Eigen took her first trip to the British Virgin Islands in December 2020. Around that time, it had one of the world's lowest Covid rates among islands that had reopened.

The 42-year-old mother of four from Sands Point, New York, has since returned twice, checking infection rates — and vaccination statistics — before her trips.

"The staff at Oil Nut Bay is entirely vaccinated," she said of the luxury resort where her family stayed. "The property is not accessible by land and very closely monitored by sea."

The British Virgin Islands are part of a rising number of Caribbean destinations that attract vaccinated travelers — while proving less attractive to unvaccinated people.

Along with Barbados and St. Lucia, the British Virgin Islands allow unvaccinated travelers to enter only if they quarantine for a duration. Data shows few are willing to do so, especially when they have other options in the Caribbean that don't require quarantines or vaccine certificates.

The relative strictness or leniency of entrance requirements in the Caribbean is reshaping travel trends in the region. Unvaccinated travelers are gravitating to the islands that will let them in, while the vaccinated want places that keep the unimmunized out.

Vaccinated travelers only

At least seven Caribbean nations and territories have announced mandatory vaccination policies for incoming adult travelers — Anguilla, Grenada, St. Barts, St. Kitts and Nevis, Trinidad and Tobago, Turks and Caicos, as well as the Cayman Islands.

The Cayman Islands plan to admit vaccinated travelers from Sept. 9 to Oct. 13 during the third phase of its structured reopening. Thereafter, the territory may let unvaccinated travelers enter if they quarantine for 14 days.

Safety is cited as the main reason behind the requirement, but such policies may also be good for business.

Marketing technology company Zeta Global analyzed site traffic to the main tourism websites of several islands after they announced vaccinated-only policies, said Eric Bamberger, senior vice president of hospitality at Zeta Global. 

Following the announcements, travel interest increased to all of them:

• Grenada — up 25%
• St. Kitts and Nevis — up 26%
• Cayman Islands — up 44%
• Anguilla — up 59%  

The data showed two trends emerging in the Caribbean, said Bamberger.

"People have more interest in traveling to islands where there are vaccination protocols in place," he said. "And their interest among other islands without vaccination protocols is waning."  

Data from travel marketing company Adara indicates enthusiasm for vaccinated-only entrance policies. Searches and bookings spiked when Trinidad and Tobago announced it was reopening only to immunized travelers — and then again when the policy was implemented.  

Adventure travel company Intrepid Travel is seeing a preference for destinations with more restrictions, said Matt Berna, the company's managing director of North America. 

"We have found our customers to be more interested in traveling to Caribbean destinations with more strict and firm policies and travel restrictions related to Covid-19," he said.

For example, among the most popular trips being booked by North Americans, "none of our tours in Mexico are in the top 20," he said. Mexico has lenient Covid protocols, but Intrepid Travel does not. Starting Sept. 1, all travelers and tour leaders with the company must be vaccinated, said Berna.

Eigen told CNBC she considered going to Mexico at one point, but found it "scary" to visit a country with few restrictions.

"I am vaccinated and would love to go to an island that only allows vaccinated people in," she said, a view echoed by several travelers who spoke to CNBC.

Caribbean authorities are expressing a positive response to the policies.

"Our arrival figures have been consistent, and load factors continue to improve," said Petra Roach, the CEO of Grenada Tourism Authority.

Turks and Caicos prepared itself for mixed feedback when it announced its policy earlier this month, said Jamell R. Robinson, the islands' minister of health and human services.

However, "we have received a hugely encouraging overall response from new and existing visitors," he said. "We anticipate it will have a long-term positive impact on bookings."

No vaccine required

In contrast to islands with relatively strict policies, places such as the Dominican Republic, Jamaica, the Bahamas and the U.S. Virgin Islands have entrance policies that rely on testing rather than vaccines.

Data from Adara suggests travel interest was highest to the Dominican Republic before other Caribbean islands put vaccination mandates in place beginning earlier this summer. Most travelers to the Dominican Republic don't need to present a negative test, but some are subject to Covid-19 breath tests upon arrival.

As vaccination rates increased among the island's top markets — namely, the United States and Canada — travel interest dropped. Covid infection rates in the Dominican Republic decreased from June to August, but interest and searches did not rebound accordingly.

Site traffic increased to the main tourism websites for Jamaica and the Bahamas in June and July, but visitors spent less time searching and clicked fewer pages, said Zeta Global's Bamberger.

 "These trends show that … travelers still have more tentative feelings about traveling to areas without vaccination policies," he said.

Similar sentiments may apply to travelers' desire to fly. A study by the financial website FinanceBuzz published this month indicates more people would be likely to fly (48%) if airlines required vaccinations, than the amount that disfavors such a policy (27%). 

Line in the sand

These figures suggest that islands with lenient protocols — i.e., those without quarantines or vaccine mandates — are likely attracting unvaccinated travelers while deterring vaccinated ones.  

"Vaccinated people want to vacation in places that had stricter requirements, so they aren't mixing with the unvaccinated," said Adara's chief marketing officer Carolyn Corda.

CNBC asked the Dominican Republic, Bahamas and Jamaica for the percentage of incoming travelers who aren't vaccinated. The Bahamas said it was unable to provide that figure. Jamaica and the Dominican Republic did not respond to CNBC's request.

Puerto Rico's tourism authority, Discover Puerto Rico, has said that the island has a vaccine mandate, though it does not have one.

Discover Puerto Rico's website says that "vaccinations are required" for guests and employees in its hotels, house rentals, restaurants and bars. Discover Puerto Rico's CEO separately confirmed the vaccine "mandate" to CNBC.

But a closer look at Puerto Rico's restrictions shows that a negative Covid test on arrival, and weekly negative tests afterward, will suffice without a vaccine. Asked for clarification, a representative for Discover Puerto Rico told CNBC that "the 'mandate' refers to the need for either vaccination or frequent negative testing."

Discover Puerto Rico's CEO Brad Dean said vaccination rates among travelers to Puerto Rico rose from 9% in May to 58% in August.