Memorial Day weekend traditionally marks the start of summer vacation nationwide. This year, vacation travel will be more individual, and a new date might determine the kickoff of many Americans’ summer trips: their vaccination day. At press time, nearly 15 percent of the U.S. population has been fully inoculated against the coronavirus, and as the number climbs, more people will be able to shift from dreaming of getting away to actually doing it. New opportunities are rising alongside the vaccination figures: Several countries and cruise ships are welcoming back visitors with proof of vaccination. Multigenerational travel is also returning, as more grandparents receive the kiss of the needle. Of course, every trip comes with a public service message. The Centers for Disease Control and Prevention still discourages nonessential travel — for now. Sean O’Leary, vice chair of the committee on infectious diseases for the American Academy of Pediatrics, said, “It’s an evolving situation. By summer, the CDC may loosen its guidance.” In addition, the vaccine is not kryptonite against the virus. Vaccinated individuals can still potentially contract and transmit the disease. Children, who are not yet eligible for the shots, are at a lower risk than adults and adolescents of contracting and transmitting the coronavirus, but it’s still possible. With summer on the horizon, here is what you need to know about travel and vaccinations.

Q: We are planning a family trip with the grandparents, who are vaccinated, and the kids, who are not. Is it safe for all of us to travel together?

A: Earlier this month, the CDC released new guidelines for social gatherings involving vaccinated and unvaccinated participants. The agency said the two groups from “a single household” can mix indoors, without masks or social distancing, as long as none of the unvaccinated family members is medically compromised. “If the grandparents were vaccinated, it would be okay [to vacation together], depending on the state and country guidelines,” said Yvonne Maldonado, a pediatric infectious-disease specialist at Stanford University’s School of Medicine in California. To be safe, all vacationers should limit contact with outsiders before and during their trip.

Q: What are some safe summer vacation ideas for a family that is not fully vaccinated?

A: Kawsar Rasmy Talaat, a vaccine expert in the department of international health at the Johns Hopkins Bloomberg School of Public Health, said the vaccine has reduced the anxiety but not the threat of transmitting or contracting the virus. Therefore, travelers should make prudent decisions when planning a summer vacation. “Until we are protected, we must continue to be careful and wear masks,” she said. “I wouldn’t recommend a big beach house right now.”

To be sure, it’s not as fun as scouting for an ocean-view property or kid-friendly beach, but it’s important to research the percent test positivity (it should be in the low single digits), spread of variants and safety mandates (or lack thereof) in your destination. “What are the risks of where you are going?” O’Leary asked.

Maldonado said the advice from last summer still holds, with the exception of liberated older travelers. “What we said last year is still true,” she said. Families need to maintain their social pods — whether the members are related or close friends — and choose outside activities over indoor attractions and roomy environments over crowded settings. “Outdoor vacations are the best — camping, hiking,” she said.

If you plan to fly, sandwich the unvaccinated travelers between the vaccinated ones. Medical experts recommend holding off on the family cruise at this time. “Ninety-five percent effective is really good, but put 4,000 people together on a ship and that’s 5 percent of 4,000 people,” Maldonado said, calculating the efficiency rate of the vaccine among the number of cruisers. (The total is 200.)

In terms of timing, Talaat suggests waiting until after spring break, in the event that cases surge in your vacation spot. “It’ll be interesting to see if there was an uptick and relaxing of the guard,” she said. You won’t have to refrain from booking for too long: Spring break ends in early April.

Q: Which domestic destinations are waiving testing and quarantining requirements for vaccinated visitors?

A: Not many cities and states still require travelers to show proof of a negative test and/or self-quarantine, but most of the remaining few have jettisoned those requirements for vaccinated out-of-towners. Among them: Chicago, Maine, Massachusetts, Rhode Island, Vermont and New York. Island vacationers hoping Hawaii will ease its restrictions will have to wait a little longer: The state’s Safe Travels program, which Kauai will rejoin on April 5, still demands testing or quarantining, with no exceptions.

Q: Which countries are accepting U.S. travelers who have been vaccinated?

A: A number of countries permit Americans to visit but require at least one negative coronavirus test result plus several days of self-quarantine. Vaccinated visitors can skip those steps and go straight into vacation mode. This month, Iceland started accepting vaccinated travelers, and Greece recently announced that it would open its borders on May 14. (The U.S. Embassy in Greece’s response to the news: “The Embassy is aware that high-level officials have spoken of intentions to facilitate summer 2021 tourism to Greece. However, there is no projected date when entry will be permitted for residents of the United States.”) Other countries that allow vaccinated travelers include Belize, Ecuador, Georgia, Guatemala, Slovenia and Estonia, according to government offices in each destination. Thailand and Australia could do the same later in the year.

Before you book an international trip, make sure the country accepts the type of vaccine you received. (Most governments approve of the big three used in the United States.) You will also need to wait at least two weeks between your last shot and your departure, so plan accordingly. For the most current information, consult the country’s tourism office or the national agency responsible for travel and health issues.

Q: Are children allowed into these countries?

A: Yes, but underage travelers may be subjected to a coronavirus test and self-quarantine. Iceland, for one, requires kids age 16 or younger to quarantine for five days and submit two negative results — one before departing and the other in-country. Belize exempts children under age 5; Guatemala excuses kids younger than 10.

Q: Is the cruise industry requiring vaccines?

A: The U.S. cruise industry is waiting for the CDC to release its guidelines for ships carrying at least 250 passengers and crew members. The health organization has not hinted at whether it will recommend mandatory vaccinations. “It’s a big question mark,” said Chris Gray Faust, managing editor at Cruise Critic. Several cruise lines in North America have proceeded without the answer, though all have embraced the vaccine mandate. This position stands in sharp contrast to some lines in Asia and Europe that do not require the vaccine. “It’s a line-by-line decision,” Gray Faust said, “because there is no country requirement.”

American Cruise Lines, which set sail this month with reduced capacity, requires vaccinations for departures through April 10, but the requirement may not apply to future voyages. American Queen Steamboat Company and Victory Cruise Lines will only accept vaccinated passengers on its domestic cruises starting July 1. The larger lines that have moved their operations to the Caribbean, Bahamas and Bermuda for the summer cruising season will only allow vaccinated adults onboard, but their policies for children vary. Crystal Cruises, which will sail from Nassau or Bimini in the Bahamas, will not accept any unvaccinated passengers, no matter the age. (Despite its rule, the company set a record with almost 4,000 passengers booking passage on its 16 voyages over 24 hours.) Celebrity, which will depart from St. Maarten, and Royal Caribbean, which will sail from Nassau and Bermuda, will require testing for minors. Virgin Voyages, the new cruise line by Richard Branson, was always adult-only; its vaccination rule reaffirms that policy.

Q: What about tour operators?

A: To date, most companies that plan group or escorted tours are encouraging vaccinations but not mandating them. “I would love to require vaccines, in the same way I’d love to require travel insurance,” said Peggy Goldman, president and founder of Friendly Planet Travel. “But I don’t think we can.”

Trafalgar will gladly accept vaccinated guests as well as ones who submit a negative test result. Backroads states on its website: “Strongly recommending all guests* get vaccinated before traveling with us on any trip regardless of regional entry requirements.” The asterisk refers to travelers age 17 and younger. Tauck is singing a similar tune: “We certainly believe that it is a good idea to receive a vaccination as soon as one becomes available to you.”

Q: What is the vaccine passport, and will I need one to travel internationally?

A: The vaccine passport is a secure digital record of your health documents stored on your smartphone or gadget, so you can easily share, say, proof of a vaccination, with the airlines or government authorities. Think of it as the 21st-century version of the yellow fever card. “You have a QR code on your phone and you scan it and your testing or vaccine status comes up,” said Robert Quigley, senior vice president and global medical director in the Americas for International SOS. “I think it’s going to be the ticket to future travel.”

Several organizations and companies are developing the technology, such as the International Air Transport Association, which created the Travel Pass; IBM’s Digital Health Pass; American Airlines, which uses VeriFly; and ICC AOKpass, a partnership with International SOS, MedAire, the International Chamber of Commerce and SGS, which provides testing, verification and certification services. The mobile app is in the experimental phase. For example, passengers flying between Singapore and London on Singapore Airlines have been trying out IATA Travel Pass, and volunteers on Air France flights from Los Angeles and San Francisco to Paris have been sampling AOKpass.

No country or travel industry player has committed to the idea, but Spain’s tourism minister recently announced plans to introduce a vaccine passport by mid-May. The European Union is also considering a vaccination passport for its member states. The “digital green certificate” could be ready by June.

Please Note

Potential travelers should take local and national public health directives regarding the pandemic into consideration before planning any trips. Travel health notice information can be found on the Centers for Disease Control and Prevention's interactive map showing travel recommendations by destination and the CDC's travel health notice webpage.

The coronavirus pandemic has disrupted travel domestically and around the world. You will find the latest developments on The Post’s live blog at www.washingtonpost.com/coronavirus