The UK is the latest country to consider COVID-19 booster shots for travel. As the government rolls out the booster program to the under-50s, prime minister Boris Johnson said three shots, rather than two, could soon be the requirement of the COVID pass that allows people to travel and bypass self-isolation.

The UK is joining the US and several other countries by offering booster shots to more adults amid fears of waning immunity. At a press conference this week, Johnson said that rolling out top-up doses is key to avoiding domestic restrictions and will make "life easier in all kinds of ways," for those who are eligible, including for international travel.

“It’s very clear that getting three jabs—getting your booster—will become an important fact," Johnson said via the Guardian. "As we can see from what’s happening, the two jabs sadly do start to wane, so we’ve got to be responsible and we’ve got to reflect that fact in the way we measure what constitutes full vaccination."

Read more: How will Europe's new COVID-19 restrictions affect your travel plans?

Police officers monitor compliance with the lockdown in Innsbruck's old town during the first day of a nationwide lockdown
Austria has rolled out booster shots as it battles a fresh wave of COVID-19 © Getty Images

As the effects of the second dose gradually wear off, more countries are requiring a third shot for improved immunity and aspects of daily life and travel. The Centers for Disease Control and Prevention CDC) reports that about 15% of adults in the US have received a top-up dose as it widens its booster program, though the US is not currently requiring one for travel.

What countries require booster shots for travel?

In August, Croatia became the first country in the EU to add an expiry date to vaccine passports in line with when the holder was inoculated. According to the government, travelers need to present a negative COVID-19 test result to enter Croatia if more than 270 days (nine months) have passed since their last dose of an approved vaccine. Austria also placed a 270 day maximum validity period on their vaccination certificates for travelers, while Switzerland has an 12-month time limit and Israel has a six-month limit in place.

In France, where the booster shot is being rolled out to the over-65s, it has become a requirement of the health pass that people use to visit restaurants, museums and to board long-distance trains. How the UK will enforce a similar requirement is not yet clear. The NHS app does not currently display booster shots on the COVID pass but Johnson said the government was "making plans" to add that function before the jabs are a requirement for travel (which the BBC reports may not happen until spring 2022).

If this trend continues, it's possible that travelers will need to stay up-to-date with their vaccines before planning any international trips. "There are currently recommendations for regular boosters for many vaccines, particularly for international travelers, including influenza, hepatitis A, yellow fever, typhoid, etc.," Dr. Bob Bollinger, a professor of infectious diseases at the John Hopkins University School of Medicine, tells Lonely Planet. "Since travelers already should review their vaccinations prior to their overseas trips and get boosters as needed, it would not be a major issue to add COVID-19 vaccines to the list."

People are seen at Bank of America Winter Village at Bryant Park
New York has rolled out booster shots to its adult population © Getty Images

When should you get a COVID-19 booster shot?

In the US, the CDC has said that people who were initially vaccinated with a Pfizer BioNTech or Moderna vaccine can get a booster as soon as six months after their second dose. Any adult who got a Johnson & Johnson vaccine is eligible for a booster at least two months after the single-dose shot. The CDC has approved mix-and-match vaccines for boosters too. This timeframe and application is widely applied across other countries. 

Will booster shots become a regular requirement?

It's likely that people will continue to have vaccines administered on a seasonal basis, particularly as more COVID-19 strains emerge. But according to Dr. Bollinger, we'll have to wait and see. That's because there's still much uncertainty about how often boosters might be required. "It is certainly possible that boosters will be needed periodically for COVID-19. But we don’t yet know how frequently boosters might be needed. We also don’t yet know if, like flu vaccinations, we might need booster vaccinations that are periodically modified to protect against new SARS-CoV-2 strains," he explains.

In the meantime, if you're planning to travel and are concerned your destination may no longer consider you to be fully vaccinated if you're not yet eligible for a booster, check the local embassy or tourist board website for information on entry requirements. There may be alternative solutions such as the option to present a negative COVID-19 test result instead.

You might also like:
How to manage vaccine certifications and COVID-19 passports for international travel
What happens if I'm denied entry to a country on arrival?
Will my health insurance cover getting COVID-19 while traveling in the US⁠⁠—or abroad?

This article was first published August 2021 and updated November 2021

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