Liam Thorp, who has no underlying health conditions, is in fact six foot two and weighs around 17.5st, but the error meant NHS staff thought he had a BMI of 28,000.
The health service classes a BMI of between 30 and 39.9 as obese.
Mr Thorp, who lives in Liverpool, was told he qualified for the jab after being placed in vaccine priority group six because of his weight.
Speaking to BBC Radio 5 Live, he said: “I’ve put on a few pounds in lockdown but I was surprised to have made it to clinically, morbidly-obese.
“It really made me rethink what I was going to do for pancake night.”
Dr Fiona Lemmens, of the NHS Liverpool Clinical Commissioning Group, admitted after the incident she could “see the funny side” but also recognised it was “an important issue for us to address”.
“There are millions of GP appointments taking place every day and while we take care to make sure records are accurate, occasional data errors do occur,” she said.
After Mr Thorp was told on Tuesday that he would receive the jab “much sooner” than he had anticipated, he called his local GP to double check.
It was only when he received a phone call from the surgery the following day that the mix-up became clear.
Mr Thorp, who is political editor at the Liverpool Echo, described the “bizarre” phone call in a detailed article for the newspaper.
“A nervous sounding chap said unfortunately my details had been put into the system incorrectly when I had registered with the GP just a year ago,” he said.
“To be honest I was quite relieved as had felt strange about being invited ahead of so many other more vulnerable people.”
The man from the surgery went on to explain that rather than six foot two, Mr Thorp’s height had been recorded as 6.2cm which, combined with his actual height, had given him a BMI of 28,000.
“If I had been less stunned, I would have asked why no one was more concerned that a man of these remarkable dimensions was slithering around south Liverpool,” the journalist joked.
Both Mr Thorp and Dr Lemmens have now urged others who believe there has been a mistake in their vaccine call-up to check with their GP.
“I’d much rather somebody else who needs it earlier than me got that appointment,” he told the BBC. “I was completely cool with it. Mistakes are going to happen in such an enormous undertaking.”
Meanwhile, Dr Lemmens said the NHS was “grateful to Liam for his honesty” and implored others to do the same.
“We would encourage anyone who has received a text invitation that they think they are not eligible for at this stage, to contact their GP practice to clarify. This will help ensure that more vulnerable people get vaccinated first,” she added.
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