Jenny went on to explain her brother believed his fitness levels meant he would suffer only "mild illness" if he contracted the virus – a high probability in the UK where almost six million cases have been recorded since the start of the pandemic.
"The only pre-existing health condition he had was the belief in his own immortality. He thought if he contracted Covid-19 he would be okay," she said.
"My mum wants people to know about John. For his story to save someone's life. For pain and loss to drive people to get a vaccine."
Jenny had her first AstraZeneca vaccine on May 10 and praised the UK's National Health Service (NHS), saying at the time: "Full on tears after getting Covid jab. Really shows the collective weight we've all been carrying. So grateful to the NHS."