Though the influenza H3N2 strain, a variant of the flu currently making headlines, has sometimes been termed a “superflu,” Dr Suzanne Wylie, GP and medical adviser for IQdoctor, told HuffPost UK that “the term ‘superflu’ isn’t a recognised medical diagnosis.”

Instead, she said, it usually describes, “A combination of genuine influenza, circulating Covid-19 variants, RSV, and other viral illnesses that overlap in symptoms and timing.

“This can make the overall picture feel more intense and prolonged than a typical flu season.”

This is not to say, however, that the NHS is not experiencing an extraordinarily busy flu season (they are), or that patients are not “experiencing symptoms that persist longer than usual”.

Here, the GP shared how to spot “normal” flu from what some might term a “superflu,” as well as why influenza might be so rife right now.

Dr Wylie explained that her definition of what some might term a “superflu” is “co-infection with more than one virus, or catching a second virus before fully recovering from the first”.

In that context, she explained, “true influenza tends to come on very suddenly, often within the space of a few hours.

“High fever, profound fatigue, muscle aches, headaches, a dry cough and a sense of being completely ‘wiped out’ are characteristic. People often describe being unable to get out of bed or perform basic tasks.”

She added, “What’s sometimes labelled this year as ‘superflu’ is essentially this classic influenza picture, but with the added complication that many individuals are experiencing symptoms that persist longer than usual, lingering coughs, extended fatigue, and a slower return to normal activity.”

And, the GP said, many cases of what people believe to be flu are actually a bad cold or another respiratory infection. These “develop more gradually” than flu, “with runny noses, sore throats, congestion and milder fevers.”

You will typically still be able to function somewhat with a cold, she continued.

“The distinction can blur, especially when multiple viruses are circulating, but influenza tends to be more abrupt and systemically draining.”

“Immunity in the population fluctuates year to year, depending on which strains have circulated previously and how closely the current strains match the [flu] vaccine,” she explained.

“If the circulating strain is one the community has not been exposed to recently, or if vaccine uptake has been lower, more people are left susceptible, leading to higher case numbers and more severe symptoms.”

The BBC notes that many people have not been exposed to the mutated H3N2 strain much in the past few years.

This is partly, Dr Wylie said, “the after-effects of the pandemic: reduced exposure to seasonal viruses over several years means people’s baseline immunity to common respiratory pathogens may be lower than it once was.”

And increased strain on healthcare may mean that people are waiting longer to get help for the flu, meaning they’re worse off by the time they’re seen, she added.

“Environmental and behavioural factors also play a role: winter gatherings, indoor living, and schools acting as hubs for virus transmission all contribute to a more intense season,” she continued.

“Many patients are also experiencing simultaneous stresses, poor sleep or chronic conditions that can make any viral illness feel harder to shake off.”

So, “the combination of genuine influenza, overlapping viruses, reduced background immunity and a challenging winter has created the sense of a particularly tough respiratory season.”

And while Dr Wylie is sceptical of the use of the word “superflu,” she advised: “If someone is unsure whether their symptoms are typical of a cold, flu or something more serious, it’s always sensible to seek medical advice, especially if symptoms are severe, prolonged or worsening.”