Doctors explain 'key symptom' that could mean you have 'super flu' sweeping across the UK

While most of the UK was enjoying the Christmas and New Year festivities in recent weeks, there were plenty who were feeling less than merry after contracting 'super flu'.

The NHS has been warning about the viral infection for months now, suggesting that thousands could die in what was expected to be the worst flu season in decades.

Prof Nicola Lewis, the director of the World Influenza Centre at the Francis Crick Institute, said: "We haven't seen a virus like this for a while, these dynamics are unusual.

"It does concern me, absolutely. I'm not panicking, but I am worried."

The flu mutated from an illness in the summer, and is said to be 'super infections', 'hotter' and 'nastier' than the usual flu strains we see around winter time.

Although we do have the flu jab, which usually helps older and more vulnerable people stave off the symptoms when the temperatures start to drop, this strain looks to have mutated beyond this year's vaccine, leading to a huge increase in hospitalisations and GP visits.

Hospitals have been under real pressure this winter (Getty Stock)

Dr Victoria Shotton, a GP in Scotland, explained that her surgery was admitting three times as many patients with flu compared to this time last year.

She said: "We are seeing a massive increase in presentations on a daily basis. It has started early this year and is more severe than last year.

"Unfortunately, it looks like this year's jab isn't offering the same protection as last year.

"Through no fault of anyone involved, it isn't quite covering the main strain that's going around.

"However, that doesn't mean that it's not worth getting because it will still offer some protection and prevent the flu from getting so serious that you need to go to hospital."

While the flu already comes with unpleasant symptoms such as severe chest pains, vomiting and diarrhoea, doctors have now explained that one particularly brutal symptom might be a key sign that you've contracted it.

A huge number of people have been reporting that they've been throwing up yellow bile, the liquid which is produced in the liver and helps to break down fats in the small intestine.

Vomiting yellow bile is said to be a key sign of the infection (Getty Stock)

Dr Simon Clarke, an infectious disease expert at the University of Reading, said: “Vomiting bile happens because someone is vomiting on an empty stomach."

A number of leading virologists agree that because the flu strain suppresses the appetite, people are vomiting on an empty stomach, which is why they throw up the yellow bile.

Professor Paul Hunter, a leading infectious diseases expert, suggested that it happens 'because of inflammation of the stomach lining.'

"It is often mistakenly called ‘stomach flu’, but you can get it as part of the flu," he added.

If you are suffering from this symptom, the best thing to do is drink lots of water, as it's key to stay hydrated while you're suffering from the flu.