“I’ve never felt so ill in my entire life – I’d not wish it upon anyone,” says Joseph Sullivan of his experience with flu.

Joseph, 26, spent 24 hours in hospital last Christmas but believes the consequences may have been even worse if he had not been vaccinated.

The type 1 diabetic with auto-immune liver disease, from Cowbridge in Vale of Glamorgan, has joined health officials in urging thousands of people to take up the offer of flu jabs this winter.

Last year, although nearly three quarters of the over 65s got the jab, only 39% of those younger people from vulnerable groups had a flu vaccine.

More people are expected to fall ill with flu this winter and up to 1,000 patients a week with flu could end up in hospital beds.

It has been seven years since flu cases in the community hit high intensity levels, and it has been overshadowed by the Covid pandemic and a period when people socialised far less.

However, health officials are not complacent. Last winter, patients in hospital beds with flu peaked at 250 a week in February.

The most likely scenario is that about 440 flu patients a week will end up in hospital this winter.

Mortality rates show deaths due to flu and pneumonia are nearly three times those caused by Covid over the last 12 months.

“It’s a tragedy in many ways, when people have really serious infection that puts them in hospital, or may actually lead to them dying, when it is possible that taking up those free vaccines for them could have prevented that,” said Dr Chris Johnson, who leads the vaccine programme for Public Health Wales (PHW).

On top of flu, hospitals could face extra pressure from more patients with Covid – although those numbers rise and fall across the year.

This could rise to between 24 and 156 admissions a day.

Another pressure comes from respiratory syncytial virus (RSV), with children under five particularly vulnerable. Scientists have modelled up to 63 daily admissions this winter, with symptoms similar to a bad cold and also bringing a loss of appetite.

When all three viruses are combined, early January could bring a daily peak of 126 admissions in the most likely scenario.

“These diseases are really, really life threatening in some cases, we know that they lead to hospitalisations, people being sick – just disruption to people’s lives that could possibly be avoided just with a simple vaccination,” said Dr Johnson.

He is trying to reach 467,000 people in Wales classed as clinically at risk, which covers conditions such as asthma, COPD, diabetes and liver or respiratory disease.

Joseph is one of 99,000 people living with diabetes in Wales. They are six times more likely to die from flu and are also at high risk from Covid.

He was diagnosed with type 1 diabetes in 2016 while at his first year in university, then the following year was diagnosed with an auto-immune liver disease, making him more vulnerable.

While he manages his conditions well, he ended up in hospital with flu last Christmas.

“I think for the sake of having a sore arm (with the vaccine), I would trade that any day over having flu,” said Joseph, who works for a startup company called Love to Visit.

“It’s the most ill I’ve probably ever been, and it has definitely made me a lot more wary going into this winter now, I would do anything not to have flu again ever.”

Last year he attended his brother’s wedding the week before Christmas, but became unwell days afterwards, and ended up in A&E.

“My blood sugars were all over the place, and it’s probably the worst I’ve ever felt in my life. It was horrendous.

“I started having my flu jab after my diabetes diagnosis, and it’s just something I’ve always had – now I’m glad I do have it, because I dread to think how I would have been if I hadn’t had it.

“Obviously, being diabetic. Needles don’t really bother me and I’m kind of used to being prodded, but it’s definitely worth having a needle in the arm and being sore for a couple of days, than getting flu.”

• The flu and Covid vaccines are being offered to all those with at-risk health conditions, all over 65 or in care homes, pregnant women and those with a learning disability, as well as homeless people.

• Flu vaccines are being offered to children, frontline health and social care staff and care home staff.

• The RSV vaccine is also being offered to pregnant women and those in their late 70s.

The modelling of winter pressures also points to an impact on emergency departments with potentially a peak of between 261 and 511 daily attendances due to respiratory problems.

The same report, prepared for the Welsh government, also suggests a likely impact of the cost of living crisis and fuel poverty on groups who are more suscepitible to flu and Covid.