New travel rules will take effect from Tuesday, affecting thousands of Irish passengers hoping to jet abroad to EU countries for a winter break.
From February 1, travel to and from Ireland across the bloc will be impacted by changes to Digital Covid Cert rules.
The measures say that from Tuesday, a 270-day validity period will be applied to the Covid Certs.
This means that for people who were vaccinated over nine months ago and have not had a booster, they will not be allowed to enter other EU countries such as Spain, Portugal, Italy and Greece.
As for travellers who have recently recovered from infection, they must prove they have a recovery cert within the last 180 days or a negative test result.
People who have availed of their booster jabs will be able to travel using their updated certs.
Around 44,000 people who were fully vaccinated before May 1 last year have yet to receive a booster shot, meaning they will be barred from travelling overseas to EU nations from Tuesday.
Travel expert Eoghan Corry explained how the new rules will work and how they could potentially be a "nightmare" for some travellers.
"The common strategy comes into force tomorrow, if it's nine months since you completed your full course, [destination countries] will start looking for proof of your booster," he told RTE's Today with Claire Byrne programme.
"If you don't have that, we're back to testing which was the situation before July, so you can still travel but you will need a [professionally administered] antigen test.
"Most Irish people got their second shots in July/August so it'll be around St Patrick's Day it will kick in.
"Some health workers will have hit the nine months before Christmas.
"If you are in the system you will get a new QR code so it's a good idea to stick that on your phone and have it ready for travel from tomorrow even though it might be a few weeks before you meet the nine months.
"Once you have that, it's business as normal."
The updated Covid Certs are being delivered "remarkably efficiently", he added, in some cases within hours after people have received their booster vaccine.
However, he acknowledged it is a "bit of a nightmare" for those people who are experiencing delays in their updated certs being administered.
"If you have been to one of the big vaccination centres it's fine, if you've gone to a pharmacist or GP, the processing of that is slow and it was slow for the Digital Covid Cert before," Mr Corry said.
"Waiting game is all I can say but remember you do have the option of the antigen test, and there are a lot of people who for some reason cannot get the booster, so they're back into where they were before July."
He added that the new rules are "pretty straightforward" when it comes to children.
Kids under 12 are generally not required to get tested throughout Europe, but there are some exceptions, including for entering Italy and Greece.
He warned that people should be aware that these two countries, as well as Portugal, have already introduced testing requirements so even if people do have their Covid Certs, they will still need to show proof of a negative test when landing.
Mr Corry added that the new rules only concern travel within the EU, as different regulations will apply when entering countries outside the bloc.
