Rhiannon Ingle
There's a new flu strain that is spreading rapidly across the Northern Hemisphere at the moment.
The surge in cases of the new strain has prompted health officials to warn of a potentially severe flu season ahead in the United States.
Data collected by the US Centers for Disease Control and Prevention on Friday (21 November), reveals that standard flu vaccines may offer reduced protection against the variant currently driving infections across the country.
The CDC, which monitors influenza activity nationwide, reports that the dominant circulating strain differs from typical H3N2 viruses. More than half of flu cases identified so far this season are attributed to a sub-variant known as subclade K.
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This finding raises questions about vaccine effectiveness as the flu season progresses, though health officials continue to recommend vaccination as an important protective measure against severe illness and hospitalisation.
According to the Global Virus Network, subclade K has 'evolved' in a way that may mean it's much more equipped to spread, leaving more people vulnerable.
Japan has already declared an influenza epidemic after experiencing waves of infections earlier than typical for the season, according to Dr Robert Hopkins Jr., medical director of the National Foundation for Infectious Diseases.
Meanwhile, the United Kingdom is grappling with a surge of severe cases that has resulted in urgent warnings from health officials about one of the country's most challenging winters in recent memory.
So, it's important to know exactly what symptoms to watch for.
The mutated H3N2 strain produces symptoms consistent with typical seasonal influenza A infections, experts note.
Key symptoms include:
Hopkins emphasises that flu symptoms typically begin abruptly - often described as feeling like being 'hit by a truck'.
Now, due to the fact that flu symptoms overlap considerably with COVID-19 and other respiratory viruses, testing is essential for proper diagnosis.
Three-in-one rapid home tests that detect influenza A, influenza B, and COVID-19 are now available and recommended by experts.
If you test positive for the flu, you can seek treatment with antivirals, which can reduce symptom severity, according to Hopkins.
However, immediate medical attention is warranted if you experience severe symptoms, high fever, signs of dehydration, or difficulty breathing.
"The flu is not just a cold. It can be quite severe," Hopkins cautions.
You can find out more about the flu on the official NHS website here.