MIAMI  — Joel Steckler was eager for his first cruise in more than a year and a half, and he chose the ship that just two months ago became the first to accept passengers again after a long pandemic shutdown.

Steckler was fully vaccinated against COVID-19 and that was enough to resume cruising, under initial guidance from the U.S. Centers for Disease Control and Prevention.

Now, the 63-year-old from Long Island, New York, is going to postpone the trip he had planned for Saturday amid new, tighter guidelines prompted by the delta-variant-fueled surge in cases and breakthrough infections.

“You just have to make a personal decision,” said Steckler, who takes medication that suppresses his immune system and changed his plans after consulting his doctor. “You don’t want to be in a position where you are sick on a cruise and you have to fly home or somehow get home.”

Cruise lines have detected infections among vaccinated crew members and passengers, including in an elderly traveler who recently died. Last Friday, the CDC began advising travelers who are at a higher risk for severe COVID-19 illness to avoid cruises. It is also recommending that passengers show both a recent negative COVID test and proof they've been immunized.

In addition to the surging delta virus, the CDC changed its cruise guidelines for high-risk groups because of the close proximity of ship passengers, the limited options for care on board and the challenges of medically evacuating travelers at sea, Centers spokeswoman Kristen Nordlund said Tuesday.

Some cruise lines — and cruise destinations — are also revising their own guidelines.

Starting Sept. 3, the Bahamas — a favored stop for cruises — is requiring all passengers 12 and older to be vaccinated against COVID-19 as a condition for ships to dock. That has prompted companies including Disney Cruise Line, Royal Caribbean and Carnival to announce this week that they are adopting the same requirement. The companies will ask for a government vaccination card or a record from a health care provider.

They've been able to do so in Florida after a federal judge this month temporarily blocked a state law banning cruise lines from requiring passengers to prove they're vaccinated.

The companies are also once again requiring masks in indoor areas of the ships and other places where people gather.

"Unfortunately, no venue on land or at sea is COVID-free right now," Carnival Corp. said in a written statement.

Carnival commented on the case of a vaccinated 77-year-old woman who later came down with the virus. The company said the woman “almost certainly did not contract COVID on our ship,” suggesting she was already infected when she embarked.

Neither cruise lines nor the federal government are reporting how many cases they have had on their ships. They have only acknowledged that there have been infections.

Officials in Belize, however, recently reported that 26 crew members and one passenger of a Carnival cruise ship — all of whom had been vaccinated — tested positive for COVID-19. They said all of them had mild or no symptoms, and were in isolation.

Jaime Katz, an analyst who covers the cruise industry for the Morningstar financial services company, said while many high-risk travelers might postpone their trips, others will continue to book for the future, betting that the current wave of cases will subside by the time their ship sails.

“Flexible booking and cancellation policies have made cruising more palatable for nervous travelers,” he said.

Companies are offering full refunds if people test positive for COVID-19 or decide to cancel after a cruise line shortens the length of a planned trip. Royal Caribbean International is also offering to fly people home if they or anyone in their party test positive during the cruise.

Chris Woronka, a Deutsche Bank analyst who follows the leisure industry, said cruisers, including those over 65, are an avid bunch — so eager to get back on the water that they won’t easily be dissuaded by the current COVID surge and more stringent travel requirements.

“I don’t think this is permanent unless we’re dealing with delta 2.0 or whatever the next one is,” Woronka said.