Flu cases are spiking earlier than usual. What you need to know.

A new flu strain that has been dominating cold and flu season overseas is on the rise in the United States.

The mutated strain, known as subclade K, originates from the most common flu-causing virus, influenza A, and one of its most common variations, H3N2. This could mean a particularly brutal flu season, especially with the current vaccine being a mismatch to the rapidly-spreading variant.

There's no need to panic yet, though - as we get deeper into flu season and more data becomes available, early evidence is emerging that the vaccine still provides good protection against serious illness from subclade K.

As family gatherings and holiday celebrations approach, here's what to know about the new flu strain.

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