The government is considering whether to introduce vaccine certificates or "passports", as part of plans to ease lockdown in England.
They could also be needed to travel abroad, with countries such as Greece and Austria keen to establish such a system.
What is a vaccine passport?
The government wants as many people as possible to be vaccinated against Covid, but it's not compulsory.
At the moment, anyone who has had the jab receives a vaccination card, and the details go in their medical records.
Ministers are considering additional ways for people to prove they are at lower risk of getting or transmitting the virus.
According to the BBC's political correspondent, Damian Grammaticas, a passport feature may be added to the existing NHS app.
This might allow people to use their phone to prove they have been vaccinated or had a recent negative test.
However, not everyone is happy with the idea of vaccine passports. A petition asking the UK government not to introduce them has more than 200,000 signatures, meaning it will be considered for a debate by MPs.
Would I need a vaccine passport to go to the pub?
A passport could theoretically allow visitors to show bars or sports stadiums, for instance, that they have been vaccinated. This could help venues feel more confident about being Covid-secure.
A review of whether such passports could help the economy recover has been announced by the government.
It will consider whether proof of a jab or a negative test could be used to gain access to an event or service, reduce restrictions on socialising and improve safety.
The review will also look at privacy and ethical issues, including how far companies will be allowed to go in requesting Covid passports.
Prime Minister Boris Johnson said people who can't have a vaccine must not be discriminated against.
The government will make its recommendations before step four of measures to ease lockdown - which is not due before 21 June at the earliest.
Will I need a vaccine passport for going abroad?
It's quite possible - for some trips at least.
In future, some countries are likely to require proof of vaccination to allow entry.
"If another country says you can't come in unless you have the jab, then we want Brits to be able to demonstrate that," Health Secretary Matt Hancock has said.
Some countries and travel companies have already announced plans:
- Greece and Cyprus will admit Covid-negative Israeli tourists this summer who can prove their status with Israel's "green" digital vaccine certificate
- Denmark and Sweden are developing vaccine passports in time for the summer
- Saga, which specialises in holidays for the over-50s, says passengers on its 2021 holidays or cruises must be fully vaccinated
- Australian airline Qantas says travellers will eventually need to prove they have had a vaccination to board its flights
Can my boss force me to get vaccinated?
Pimlico Plumbers has said it will require employees to be vaccinated, and may not keep on those who don't comply.
Care home operator Barchester Healthcare has also said all new hires must get the jab.
Justice Secretary Robert Buckland said making new staff get inoculated could, in theory, be possible if it was written into their contracts.
But he said it was unlikely bosses could make existing workers have vaccines under their current contracts.
Demanding that staff be vaccinated would be unlawful in the "majority of circumstances", says employment lawyer Ella Bond, from Harper James solicitors.
Businesses are not allowed to discriminate against people for reasons including disability, pregnancy and religious belief.
Pregnant women are not generally recommended to have the vaccine unless they are at particular risk. And the vaccine isn't suitable for people with some health conditions, including certain allergies and immune system problems.
Sarah Gilzean, a discrimination lawyer at Morton Fraser, agrees that such valid reasons for not having the jab could make it hard for employers to insist staff have vaccine passports.
"In settings where there are alternatives like mass testing that are less intrusive, it's going to be difficult for employers to justify that requirement," she says.
In her view, the only employees where there is a "good argument" that vaccinations should be compulsory are health and social care workers.
What do I need to know about the coronavirus?
- HOLIDAYS: When can I go on holiday in the UK or travel abroad?
- SUPPORT BUBBLES: What are they and who can be in yours?
- SCHOOLS: When will schools reopen?
- TESTING: What tests are available?
- SYMPTOMS: What are they and how do I protect myself?
Are you unable to be vaccinated due to pregnancy, allergies or other medical reasons? How do you feel about vaccine passports? Get in touch by emailing firstname.lastname@example.org.
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