Traveling This Summer? Here’s What You Should Know About the Delta Variant.

With vaccinations on the rise and mortality rates related to Covid-19 going down in Europe and other parts of the world, many people are making plans to travel this summer and beyond. But experts say the quickly circulating Delta variant is a new concern for travelers, particularly those who are unvaccinated.

The European Union said on June 18 that the United States would be added to its “safe list” of countries, a decision that should allow even unvaccinated visitors from the U.S. (who can provide proof of a negative coronavirus test) to enter its 27 member states for nonessential travel. These countries, however, can impose their own restrictions and requirements for entry.

The E.U. decision comes the same week that the Centers for Disease Control and Prevention elevated the Delta variant of the coronavirus to a “variant of concern” as it appears to spread more quickly and may affect people more severely than earlier forms of the virus.

If you’re wondering how the variant will affect your travel plans, here is everything you need to know before booking a flight.

So far, the variant, first identified in India, has spread to more than 80 countries as of June 16, according to the World Health Organization. In a news conference on June 10, Dr. Hans Kluge, W.H.O.’s regional director for Europe, said that the variant was “poised to take hold” in Europe.

Jennifer Nuzzo, an epidemiologist at Johns Hopkins Bloomberg School of Public Health, said this will probably be the case in other countries, as well.

“If you’re out and about this summer, chances that you’re going to encounter the Delta variant, either in the U.S. or in Europe or other parts of the world, are pretty high,” she said.

The Delta variant currently makes up between six and 10 percent of cases in the United States, said Dr. Ashish Jha, the dean of Brown University’s School of Public Health, adding that it will probably will be the dominant strain in the United States by August.

If you are fully vaccinated, particularly with a two-dose vaccine, “don’t worry about the Delta variant,” Dr. Jha said.

Millions of Americans have received either Pfizer-BioNTech or Moderna vaccines; both are two-dose vaccines. Studies have shown their efficacy drops only slightly when encountering variants.

“People who have been vaccinated still do quite well against this variant,” Dr. Jha said, “but it is one where you need a high degree of immunity to ward off, so you really need to have both of your doses of your vaccine.”

The C.D.C. has a global variant map that shows the countries where different variants have been identified, though it does not list infection rates. It also lists the risk level by country.

Using information from government sources compiled by the Our World in Data project at the University of Oxford, The New York Times has been tracking global vaccinations, showing the percentage of people vaccinated in individual countries.

You may also look online to the national health department websites for the country you are planning to visit to get more specific data.

In Britain, for instance, where the Delta variant is already the most widespread strain, the National Health Service publishes information on the spread of the variant and vaccination rates in the country.

Unequal access to the vaccine across the world has meant that poorer countries are less adequately protected, with cases continuing to rise in parts of South America, Southeast Asia and Africa. According to the W.H.O., 75 percent of vaccine doses have gone to just 10 nations.

Dr. Jha said it’s important to look at not just vaccination rates for the country, but also the vaccine that is being used there. Brazil, Turkey and other countries are relying on one or both of the two main vaccines manufactured by Chinese companies to inoculate their citizens.

“We don’t have data that the Chinese vaccines, for instance, are quite as good in general, and particularly around the Delta variant,” Dr. Jha said.

A recent study by the C.D.C. shows that the Pfizer-BioNTech or Moderna vaccines reduce the risk of infection from any form of the virus by 91 percent for fully vaccinated people. The single-dose Johnson & Johnson vaccine is about 66 percent effective at preventing infection.

“Is it complete? No,” Dr. Nuzzo said. “But is it pretty darn good to the point that I personally would relax? Yes.”

It’s possible for vaccinated people to still be infected, she said, but the cases of this happening are quite low, and even if they get infected, they are unlikely to become ill. She added that those who have symptoms are more likely to spread the virus, so “if the vaccines did a good job at keeping you without symptoms, the likelihood that you’re going to spread it is quite low.”

If you want to further improve your odds of not getting infected, she recommends continuing to follow safety protocols like wearing a mask, social distancing and avoiding crowded, poorly ventilated indoor spaces.

If you are vaccinated but your immune system is compromised, because of a medical condition or because of certain medications you take, you should heed caution. You may not be fully protected, she said.

“If you’re an unvaccinated person, that, I think, makes your travel prospects much riskier,” Dr. Nuzzo said. “I really would not advise people traveling in an era of the increasing spread of these, not only more transmissible but possibly more severe, forms of the virus.”

Dr. Jha adds that “the simple answer” for protecting yourself as a traveler is to get vaccinated. This, he said, makes the prospect of encountering the Delta virus much less risky.

“But if you are unvaccinated or with unvaccinated people, then it really does pose a substantial risk,” he said.

He adds that travelers can use other safety measures to protect themselves, like wearing masks or social distancing, “but if you’re going to be vacationing this summer, that’s a less fun way to vacation.”

Dr. Nuzzo suggests thinking about vaccination and safety measures as different layers of protection against the virus. “Each layer adds something,” she said. “Vaccination is the thickest layer of protection against all forms of the virus.”

If your kids are over 12, get them vaccinated, said Dr. Jha. But for children under 12, who cannot yet get vaccinated in the United States, he suggests continuing to follow mask-wearing and social distancing rules. He also said that getting vaccinated yourself can help protect your children.

“The single biggest thing we can do to protect kids under 12 is to make sure everybody around them, all the adults, are vaccinated,” he said. “There’s very good evidence that when adults are vaccinated, kid infection numbers go down.”

He said that he plans to travel with his children this summer, one of whom is too young to be vaccinated.

Dr. Nuzzo, who has two young unvaccinated children, said she will, as well. “We are in a phase where we have to gauge the risks and benefits of everything that we do,” she said. “Everybody’s going to make those calculations differently.”

When the initial version of the coronavirus swept the globe last spring, much of the world hunkered down, restricting domestic movement, and many countries shut their borders to nonessential travel.

Now, many nations are opening up, but concern remains about the virus, particularly about the Delta variant. Some countries are making specific changes to their entry decisions because of the variant, while others are ordering emergency lockdowns.

On June 18, Italy’s health minister said that the nation would require a mandatory five-day quarantine and testing for people coming from Britain, even if they are vaccinated, over concerns about the Delta variant. It also extended the ban on arrivals from India, Bangladesh and Sri Lanka.

On the same day, Portugal ordered a weekend lockdown for the capital region of Lisbon, as a way to curb a surging number of virus cases. Roughly half of the reported cases stem from the Delta variant.

Rules around testing and requirements to enter another country are evolving and can change quickly from one day to the next. Make sure to check the requirements for your destination country before booking your flight, but also in the days before to you travel make sure you are following the most updated rules.

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