European countries will soon accept vaccinated US travelers. Here are the documents you'll need and how to know when it's safe.

• EU representatives voted Wednesday to allow fully vaccinated US travelers to visit soon.
• Americans will need to prove they've had their shots, but the specific rules may vary by country.
• Greece and Iceland, among the few countries already open to US tourists, are accepting CDC cards.

Hold on to your vaccination cards: European Union representatives agreed on Wednesday that Americans who have been fully immunized should be allowed to visit the EU's 27 member nations. They won't have to show a negative COVID-19 test result or quarantine upon arrival, NBC News reported. Children may also be able to accompany their vaccinated parents abroad, regardless of their own vaccination status - provided that they have a negative coronavirus test.

The new travel guidelines are expected to be formally approved by the European Council later this week, meaning travel from the US to Europe could be possible this summer.

It's likely that Americans will need to show government-issued vaccine certificates to visit most European countries. For now, neither EU nor US officials have specified whether people will need to show the white vaccination card issued by the Centers for Disease Control and Prevention or other documentation.

Lisa Lee, a public-health expert at Virginia Tech, said European countries will probably have patchwork of different rules for US travelers.

"Some have said they're only going to accept electronic [vaccine records] so it can be verified," Lee told Insider. "Other people are afraid that the CDC cards are too prone to fraud and they won't accept the paper cards."

In an interview with Ouest France, French President Emmanuel Macron said foreign tourists could visit France with a "health pass" starting June 9. Macron didn't expand on what that pass would look like, though.

Spain's tourism secretary, meanwhile, has said the country is prepared to let travelers return in June - as long as visitors show proof they've been vaccinated, recently tested negative for the coronavirus, or recently recovered from COVID-19.

"One thing is clear: All 27 member states will accept, unconditionally, all those who are vaccinated with vaccines that are approved by EMA," Ursula von der Leyen, the European Commission president, told The New York Times in April, referring to the European Medicines Agency. The EMA has authorized all three vaccines used in the US: Pfizer, Moderna, and Johnson & Johnson.

Already, a few European countries - including Greece and Iceland - are allowing visitors from the US. Their policies could offer a hint at what to expect from other nations moving forward.

The US still doesn't recommend travel to Europe

The CDC currently recommends avoiding all international travel to European countries, with the exception of Iceland and the UK. (The agency says Americans can travel there for essential visits only.) Similarly, the US is denying entry to visitors from the EU or UK unless they're US citizens.

The Biden administration hasn't said whether it will remove these restrictions in the near future, but travel and aviation groups are pushing the US government to open its borders to more countries, with testing requirements in place.

For now, the US also requires fully vaccinated Americans to test negative before reentering the country.

Lee said this policy helps protect the population from highly transmissible variants that are more prevalent in other countries and might evade protection from vaccines.

"These vaccines are incredibly effective, but they're not 100% - and they're certainly not 100% or as effective against strains that we don't know about yet that might be developing through transmission, so it's still a good time to be somewhat cautious," she said.

Greece and Iceland are accepting CDC cards as proof of vaccination

As of April 19, Greece is welcoming US travelers with a few stipulations: Visitors are asked to fill out a locator form at least one day before entering or leaving the country. Americans must also provide proof that they've been fully vaccinated - a CDC card is sufficient - or present a negative PCR test.

US travelers don't need to quarantine under this policy, a change that came with the new rule. Previously, Americans entering Greece had to isolate for a week. If a person tests positive upon arrival, however, they'll be transported to a hotel, where Greek authorities will confirm the test results and ask them to stay inside for 10 days.

US travelers to Iceland can also avoid the nation's mandatory quarantine by presenting a CDC card that shows they are fully vaccinated. Alternatively, a person can provide proof that they've had COVID-19 already - either through a positive PCR or antibody test result.

But those going to Iceland still need to take another COVID-19 test upon arrival, then wait at their accommodation until the results are back (which can take up to 24 hours). Hotels in Iceland may ask to see your CDC vaccination card as well.

Bulgaria, Croatia, Cyprus, Georgia, Montenegro aren't requiring US travelers to quarantine, either, if they show proof of vaccination. Italy is similarly allowing American visitors to bypass quarantine requirements with a negative COVID-19 test.

UK residents have been able to travel internationally since May 17 - but Americans who want to visit the UK must still present a negative COVID-19 test, quarantine for 10 days upon arrival, and get tested twice during their visit.

Travel requirements aside, an international trip brings risks

Just because a country is accepting US travelers doesn't mean a visit is low-risk. For Americans trying to decide whether to travel or where to go, Lee recommended that fully vaccinated people look at two key metrics: low levels of transmission and case numbers that are declining day over day.

"If you look at Portugal, for example, the incidence is a lot lower than Spain and they're right next to each other," Lee said.

On average, Spain is recording nearly 102 daily cases per 1 million people, while Portugal is recording around 39 daily cases per 1 million people. The CDC defines low transmission as fewer than 5 cumulative new cases per 100,000 people over the prior 28 days, and moderate transmission as fewer than 50 cumulative new cases per 100,000 people over 28 days.

If you're looking to lower your risk of infection, choose less crowded locales where you're unlikely to bump into people who haven't been vaccinated. Opt out of large events like concerts or soccer matches, too.

"If you're planning a trip to the countryside, that's a very different calculus than if you're planning a trip to the middle of a bustling city," Lee said.

Of course, outbreaks can also change course quickly, so a country that looks safe now may have high levels of transmission in three months.

"Check the requirements frequently, right up until the departure date, as every country's policies are going to be changing in response to the way the epidemic evolves," Lee said.

The website Skyscanner offers real-time updates on countries' travel restrictions and quarantine requirements. Make sure to prepare the necessary documentation for each country you plan to visit.

"You don't want to get from one place to another and discover, 'Oh, whoops, they need this piece of paper or that piece of software and I don't have that,'" Lee said.

This story has been updated. It was originally published on May 2, 2021.