Part of the allure is the notion that they help newlyweds escape some of the stress of the bigger wedding they might have had at home. But with the Zika threat, “It’s very stressful,” said Lacey Seltzer, a 29-year-old jewelry designer who made plans last year to marry Justin Pollner, 28, this fall at a resort near Cancún.

Getting married on a pretty white-sand beach has been her lifelong dream, according to her mother, Mona Seltzer, and 200 guests have already secured rooms. When the warnings about Zika grew louder earlier this year, the bride-to-be said she did not want to put her friends and guests “in an uncomfortable position” so she called the Centers for Disease Control and Prevention in Atlanta and now regularly checks the agency’s website. Some recommendations, she said, have been “changing weekly.” Mexico is on the agency’s watch list, though none of its reported cases are anywhere near Cancún.

One of Ms. Seltzer’s bridesmaids withdrew on the advice of a doctor. Fourteen others were “quite on board,” she said, as was every groomsman. The wedding is still on, but “I’m not taking it lightly,” she said.

“I’m upset that it has to be a question in anyone’s mind,”” she added.

The virus is of greatest concern to anyone who may be pregnant or may plan to have children after exposure. If saying your vows in a Zika-affected country means “you’re going to lose your sister because she’s pregnant and can’t go, that’s a problem,” said Annie Lee, a wedding planner. Some couples are keeping the C.D.C.’s phone number, 800-232-4636, next to those of their wedding planner and caterer.

The virus can be transmitted via sexual intercourse as well as by insect bites. Doctors have advised pregnant patients and couples planning to conceive to avoid affected areas or take other precautions to ward off bites. (Last week, the golfer Rory McIlroy became the latest athlete to announce he would not participate in the Summer Games because of his concerns about contracting Zika.)

Travelers who do visit affected areas are also urged to postpone pregnancy, either by refraining from sex or using condoms, for as long as six months to give their bodies time to shed the virus if they get it.