London-based Australian Bec O'Connor has noticed people treating her differently — since she returned to the UK with a bad case of the flu, the marketing executive says her friends and colleagues have been on guard.

"People are definitely very conscious of catching something," she said.

Mrs O'Connor said she suffered one of the worst bouts of ill-health she had ever experienced.

"I had this awful chesty cough and I had it so badly I had to sleep sitting upright," she said.

She said in her social circles, there was regular talk of the so-called "Aussie flu" that has arrived in the UK.

"We're hearing a lot about it in the media over here," she said.

What is Aussie flu?

Aussie flu is a variant of the H3N2 subtype of the influenza A virus.

It was dubbed "Aussie flu" because it was the same type observed during the Australian winter, in which more than 170,000 people contracted the flu.

Professor John Oxford, a virologist at Queen Mary University of London, said he was not surprised people were concerned.

"We know people ended up in hospital [in Australia] and people died," he said.

"I'm not ashamed of warning people about it."

However, Professor Oxford said Australia was not to blame for it.

"It's not as though it's been generated in Australia … these viruses are on the move," he said.

Dr Helen Stokes-Lampard from the Royal College of General Practitioners agreed.

"Australia is absolutely not responsible for the flu," she said.

"What happens every year is that the flu tends to mutate and change and Australia tends to experience the newest strain first."

British tabloids are warning of the potentially deadly virus. ( ABC News: Nick Dole )

The H3N2 subtype, to which Aussie flu belongs, has contributed to an increase in hospital admissions.

However, health authorities said the overall flu spike was roughly in line with expectations in early January.

Professor Oxford said Aussie flu was not the only strain causing problems.

"So far this year in England, the main problems we've had with respiratory disease have been mainly caused not by influenza A, not Aussie flu, but influenza B, which is a different cup of tea altogether," he said.

However, he stressed the situation could "turn on its head" and Aussie flu could become more dominant.

Flu jab could fall short

UK health authorities said the local flu immunisation had been updated and would offer some protection from the Aussie flu.

But Professor Wendy Barclay, a flu expert from London's Imperial College, said designing the vaccine each year was "tricky" due to the gradual changes in the virus.

"You have to be one step ahead of the virus and guess what changes it's going to make to outrun you," she said.

Professor Oxford agreed, describing the process as a "crystal ball exercise".

"We try and predict what's going to happen," he said.

"Normally we're pretty successful, but sometimes we fall flat on our face."