Mark Hammersley is a survivor. Standing in the Welsh sun, smiling broadly with an outreaching hand to welcome me, he looks the picture of good health. 

There is no sign of the trauma. Or the desperate battle for life he fought and won.

I first met Mark as he gasped for air in Warrington Hospital's intensive care unit. It was October 2020 and the country was in the grip of the second wave of the COVID pandemic.

"The first 24 hours was critical. I was unconscious really in many ways," Mark reminds me.

He doesn't need to. The image of Mark wearing a breathing mask attached by a tube to a CPAP machine will stay with me for a very long time.

He had been admitted after becoming poorly while moving house. Mark was 57 then and his underlying health conditions put him at serious risk.

His raspy voice was barely audible over the constant bleeping of the ICU's life-saving diagnostic machines.

"I've got diabetes and I'm overweight so they're my risk factors. So to be honest for me it's still early days," he told me at the time. His underlying health issues meant Mark had to shield for most of the year. And until then it had worked.

Standing next to his bed I asked Mark if he was concerned about his health, about the possible outcome.

"I'm worried yes," he replied. "But I'm feeling safe if that makes sense."

Mark tells me now that the doctors treating him were not sure he would make it through the night. They had warned his wife that he was not likely to survive. But instead of inducing Mark into a coma and putting him on life support using a ventilator, the doctors gambled by using a CPAP machine.

The Continuous Positive Airway Pressure unit crucially keeps airways from narrowing or collapsing.

And that decision, Mark is convinced, ultimately saved his life. He is aware that the outcomes for COVID patients put on ventilators were not good.

Five years on and Mark is still feeling the impact of that devastating infection. But he is a relieved man.

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"I have been told that I have scarring on my lungs but it's not affecting their functionality, whether it will later on in life I don't know," he says.

"So at the moment it's still a process but I'm a lot better than I was certainly five years ago and it affects you in different ways. When I was in hospital and afterwards I had a lot of muscular pain so for about 18 months I probably couldn't even put a shirt on properly."

In the ICU bed next to Mark's I also interviewed a young grandmother. She was sat upright and also breathing with the help of a CPAP machine. But she was much more talkative and alert compared to Mark. She was confident her treatment was going well.

But when I returned to the hospital a few weeks later to follow up with both patients I was told she had died shortly after filming.

Mark was aware. He knows that he will live with the long-term health complications from COVID for the rest of his life. But he's still thankful, every single day for that opportunity.

The UK will mark the five-year anniversary of the start of the COVID pandemic on Sunday.

The deadly virus shut down the world after it spread from Wuhan in China at the start of 2020.

Between March of that year and July 2022, an estimated 180,000 people died after contracting COVID in England and Wales, according to figures published by The King's Fund thinktank.

The UK government said Sunday's day of reflection will be an opportunity for the public to remember those who lost their lives, as well as reflect on the impact the virus had on everyday life and pay tribute the frontline workers.

(c) Sky News 2025: Five years on from COVID, one survivor reflects on having to fight for his life