The prospect of domestic Covid passports are already the source of intense debate in the UK.
They are not yet a reality, but the government has launched a trial into the use of certification to get life back to normal - including getting in to entertainment venues, nightclubs, and sporting events.
Here ITV News answers all your questions about Covid passports - if we'll get them, what they'll look like, and when they'll come into force.
Coronavirus: What you need to know - listen in for all your questions answered on Covid passports:
How does the government know Covid passports will work?
It doesn't yet. There's currently a trial of a potential system underway and a review into the use of certification.
The results of this are likely to form the basis for any kind of passport that comes in.
The 'Covid status certification' trial looks at three ways you can show you don't have the virus: Evidence of a recent negative test; having been vaccinated; or having had Covid recently and therefore have natural immunity.
Why the heated debate?
The Prime Minister has already acknowledged there are tough ethical and moral issues at play.
For some, the idea of having to show evidence of your Covid status raises issues of privacy and the risk of discrimination.
Vaccines are not compulsory, but there are fears this scheme could put pressure on people.
Yet others see it as the only way to get back to some kind of life as normal.
That tension is something the review is exploring; whether the benefits the scheme would bring to the economy outweigh the potential infringement on people's freedoms.
Would I be carrying around a physical Covid passport?
What the Covid passport will look like isn't clear yet. The government has said its trial will allow for both digital and non-digital certificates.
A number of private developers are also working on apps that could work as a way of proving your Covid status.
It's not unlikely the system would be similar to the NHS Test and Trace app and use QR codes as a way of scanning in to a location.
Where will these be used?
The government's trial run is focusing on gatherings big and small - the FA Cup final, a cinema, a nightclub, and a fun run.
So will I need a Covid passport to get into the pub?
That question is one of the most contentious and the answer is still unclear.
Those working in the hospitality industry have already criticised the idea, calling it "outrageous" and "not thought through".
Wetherspoon boss Tim Martin said passports would be “the last straw” for struggling pubs and force bar staff into a “bitter civil liberties war” with customers.
But the argument remains that such a system, even if temporary, would be a good way to get venues open again and the economy back up and running.
If Covid passports do come in to force in the UK, when will it be?
The government's trial is running throughout April, so it's unlikely a system will be introduced before the summer.
ITV News's UK Editor Paul Brand estimates Covid passports won't come into force until all adults in the UK have been offered a vaccine.
That would be the end of July if the rollout stays on track.
It would ensure fairness in the system if having had a vaccine becomes a major component.
Can businesses bring this in - even if the government doesn't?
The government has said it's happy for businesses to bring in their own systems to check if customers are Covid-safe.
But it would be tough for standalone firms to make the necessary checks on NHS records and so on, as well as the additional cost of staffing such checks.
The move could also be a turn-off for customers if only very few places brought it in.
How are other countries using coronavirus vaccine passports?
Israel has introduced a 'green pass' system which allows people who have been fully vaccinated, or who have recovered from Covid-19, to visit large gatherings, like concerts.
The pass can be either physical or displayed on a mobile phone app.
Denmark launched its 'coronapas' system earlier this month. Either on an app or in hard-copy format, Danes have to show they have either been fully vaccinated, tested negatively in the past 72 hours, or had Covid recently.
It aims to allow people to enter non-essential shops as well as hairdressers and driving schools. Businesses that allow citizens in without a pass face fines.
France, Germany and Spain are all currently trialling different internal Covid passport systems, but all have come under sustained domestic criticism for considering the move.
Could I travel abroad with a Covid passport?
There is already a system in place whereby travellers have to prove their Covid status if travelling overseas.
For those exempt from travel bans, most countries require evidence of a negative test and there are various quarantine regulations in place around the world.
Countries popular with Brits have already signalled their intention to allow travellers entry if they can prove their Covid status, and the PM has said there is "definitely" a role for the passports in international travel.