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UK health authorities have uncovered data errors on up to 700,000 vaccine passports, meaning many fully vaccinated holidaymakers lack the certification required to travel abroad.
The errors came to light when people checking their NHS app, separate to the NHS Covid app that tracks exposure to the virus, found the vaccine passport section to be incorrect.
About 10.4 million people have downloaded the app, 6 million more than had before May when the Covid travel pass was added, according to The Telegraph.
Freedom of Information requests from the paper revealed 677,331 cases where Covid vaccine records have required correction.
Experts believe the figure represents a just a tiny proportion of erroneous passports in the system.
To combat the clerical nightmare, the UK health service is launching a Vaccination Data Resolution Service, a seven-day service to "support citizens resolving problems they encounter with their Covid-19 vaccination records".
Such was the frustration felt by one man affected by the NHS's administrative aberrations that he resorted to a rather extreme measure.
"Two weeks ago I decided I had had enough, so I took drastic action. I went and had a third vaccination," he told The Telegraph.
"This has now shown up in the app as my second vaccination and it appears as though I'm fully vaccinated and good to travel, and can now use the domestic pass for the theatre."
In the UK's traffic light for international travel system, fully vaccinated people can avoid quarantine when returning from green and amber-list countries.
UK travel: green, amber and red list countries from August 26
The emergence of the blunders is the latest spanner in the works for the UK government's controversial Covid pass plans.
In July, UK Prime Minister Boris Johnson announced that two vaccine shots would be required to gain entry to England's nightclubs from the end September.
But this appeared to go against an official letter from Health Secretary Sajid Javid earlier in August, in which he said no final policy decision had been made. The NHS said it was contacting people experiencing problems with the issue.
"The vast majority of updates made to vaccination records by NHS digital do not relate to people's vaccine status," a statement said.
"The NHS is proactively contacting people who have been vaccinated in England and are showing an incomplete record so their records can be urgently corrected."