As vaccinations ramp up and regulations loosen for people in the United States, many are planning travel for summer and beyond, with experts predicting that July 4 will be the biggest travel weekend since the beginning of the pandemic.

But with regulations shifting, people might have questions about testing or vaccination requirements for their trips. The Centers for Disease Control and Prevention recently eased travel recommendations to more than 100 countries. Some countries are completely open to vaccinated travelers, while others require a negative coronavirus test result in order to enter.

In the United States, the CDC has advised that vaccinated people no longer need to wear masks in most places and released new travel guidelines that said domestic travel is safe for them. But travelers must take note of local advice and regulations, as these can vary state by state.

Here’s everything you need to consider about testing and vaccinations before you travel within the U.S. or internationally.

Are there testing and vaccination requirements for domestic travel?

For most places, no. You do not need to be vaccinated for any domestic travel. Hawaii is the only state that requires a negative test for travel.

In Hawaii, the test must be administered within 72 hours of arrival and the results uploaded to its Safe Travel platform to avoid a mandatory quarantine when entering the state or for some inter-county travel, though the latter restrictions are set to end on June 15.

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Alternatively in Hawaii, you can also provide proof that you’ve recovered from COVID-19 in the past 90 days, including both a positive test result and a letter from a doctor clearing you to travel.

The state’s governor, David Ige, said this month that people who received their vaccination in the state of Hawaii may bypass testing and quarantine requirements starting on June 15, and that anyone vaccinated in the U.S. will be able to enter Hawaii without testing once the state has reached a 60% vaccination rate.

If you are unvaccinated, you should continue to adhere to social distancing and mask-wearing protocols while traveling domestically, the CDC said. You can use the CDC’s Travel Planner to check guidelines by state.

What are the testing and vaccination rules for international travel?

While testing and vaccination requirements vary by destination country, everyone arriving in the U.S. — even vaccinated Americans — must present a negative test result upon entry.

Many nations are still closed to American travelers. Those that are open may require a negative test, proof of vaccination or evidence of recovery (or a combination of these) to enter.

The United Kingdom, for instance, requires that American travelers, regardless of vaccination status, provide proof of a negative test taken within 72 hours of departure, quarantine upon arrival and take two additional tests during their stay. Children under 11 are exempt from these requirements, as are some other people depending on their reason for travel.

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Some European countries are allowing in Americans who are vaccinated or who can show a negative test, with more expected to follow suit.

Canada is still closed to Americans, with few exceptions, and will remain so until at least early July, said Patty Hajdu, the country’s minister of health, in a news conference in June.

The U.S.-Mexico land border is closed for nonessential travel until at least June 21, but air travel is allowed and the country does not require a negative test for entry. Because of its high risk level, the CDC recommends that travelers be fully vaccinated before traveling to Mexico.

Consult the CDC’s inventory of international travel health notices for more information on regulations by country.

“Travelers should always check with their airline and the embassy of the country they are visiting to ensure they have the proper documentation required to enter the country,” said Perry Flint, a spokesman for The International Air Transport Association, a global airline industry group.

What test should I take, and where and when?

To enter the United States, travelers must show a negative result to a nucleic acid amplification test (NAAT) — PCR is a type of NAAT test — or an antigen test, also known as a rapid test, taken in the three days before departure, according to the CDC.

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Some airports offer on-site testing, such as Heathrow Airport in England, or Rome’s Fiumicino International Airport in Italy.

Josh Alexander, a New York-based luxury travel agent for Protravel International, said that many international hotels, including most Four Seasons hotels and resorts, are offering on-site rapid tests for free or at a nominal cost.

Testing at local clinics is also available in many places, though you should check availability at your destination ahead of time and book if you can. It may also come at a high cost. Alexander said that PCR tests abroad can range from $50 to $150.

The CDC said that it allows for a three-day time frame rather than 72 hours to allow flexibility in the time of day the test can be taken. For instance, if you are flying out on a Friday, the test may be taken at any time on Tuesday.

But, when it comes to international destinations, Alexander recommends erring on the side of caution when timing your test by calculating it based on time of arrival at your destination.

“Rules are constantly changing,” he said, “so we’re just trying to always tell people they should always be as conservative as possible to eliminate any gray area.”

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What are the requirements for minors?

The CDC testing recommendations apply to all children 2 years and older, which means your toddler also needs to deliver a negative COVID-19 test to enter the U.S. from abroad. When traveling, children should wear masks, practice social distancing and wash hands often, the CDC said.

“If the kids are age 12 and older, get ’em vaccinated,” said William Schaffner, an infectious disease expert at Vanderbilt University, in an email.

If you’re traveling to a country within the European Union that is open to travelers from the U.S., children who cannot be vaccinated should have a negative PCR test taken no more than 72 hours before arrival at your destination, and additional testing may be required upon arrival.

Travelers should check with their airline or destination country website for relevant requirements.

What if I want to go on a cruise?

Rules vary from one cruise line to another, with some planning to require that all passengers and crew be vaccinated, and others adopting a hybrid model.

But recent laws passed in Florida and Texas banning businesses from requiring proof of vaccination to use their services may complicate this plan.

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Celebrity Cruises, set to be the first U.S. cruise ship to restart operations on June 26 from Fort Lauderdale, Florida, said it’s optimistic that a resolution would be reached in time. It is requiring that guests 16 years and older be vaccinated, while children will be tested at the terminal.

Carnival Cruises said on Monday that its first ship would set sail from the Port of Galveston, in Texas, on July 3 and would be available only for vaccinated passengers. Norwegian, which will begin to operate cruises from Miami in August, said it will require the same through October 31 and has threatened to skip Florida ports if the state does not allow cruise lines an exemption from the law banning vaccine requirements.

Christine Duffy, the president of Carnival Cruise Line, said in a statement on June 7 that “the current CDC requirements for cruising with a guest base that is unvaccinated will make it very difficult to deliver the experience our guests expect, especially given the large number of families with younger children who sail with us.”

“As a result, our alternative is to operate our ships from the U.S. during the month of July with vaccinated guests,” she said.

But even if you are vaccinated, you must also consider the requirements of the country where the cruise is disembarking. The Caribbean island of St. Maarten, for instance, where Celebrity Cruises started sailing on June 5, requires a negative test in addition to proof of vaccination.

What documents should I bring with me if I travel?

This will also depend on where you’re going, but a good rule of thumb is to carry your physical vaccine card, if you have it, and proof of a negative test, if it is required.

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Alexander, the travel agent, recommends people bring the original documents. While a number of digital health certificates — which show vaccine status and test results — are in the works, he said, they are not yet widely accepted. You should check, also, that your document is in the correct language. The United Kingdom, for instance, requires that test results be in English, Spanish or French.

CommonPass, from the Geneva-based nonprofit the Commons Project Foundation, and the IATA Travel Pass are two apps providing digital access to vaccine and testing records for travel. The European Union will be releasing its own digital COVID certificate for EU citizens by July 1, though it is unclear whether Americans will be able to use it.

You should check with your airline to see if the app you want to use will be accepted at your destination. Both the CommonPass and IATA websites list destinations and airline partners accepting the digital health certificates.

Alexander added that some countries, such as Croatia, may also require proof of a return flight or confirmation of your hotel booking or other accommodation, though this is rare. In South Africa, which has implemented a curfew, travelers may need to show their flight ticket to law enforcement officers to show they are allowed to be in transit.

But these shifting regulations should not dissuade people from traveling, Alexander said.

“If you’re vaccinated and you’re following safe precautions, you can still have a great experience,” he said.

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This article originally appeared in The New York Times.