Once the foreign travel ban is lifted on May 17, Downing Street said those going abroad could open the app upon arrival to prove they have had two doses.
Those without smartphones were told to call 119 to order a letter confirming their vaccination status.
The app, developed by NHS Digital and NHS England, was originally designed to allow people to book appointments, repeat prescriptions and see their full medical records.
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Official guidance from the Government published online states: “You can access your Covid-19 vaccination status through the free NHS App from May 17.
“You can access the app through mobile devices such as a smartphone or by tablet.
“Proof of your Covid-19 vaccination status will be shown within the NHS App. We recommend you register with the app before booking international travel.
“Demonstrating your Covid-19 vaccination status allows you to show others that you’ve had a full course of the Covid-19 vaccine when travelling abroad to some countries or territories.
“A full course is currently two doses of any approved vaccine.”