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It’s cold and flu season again, which means you could be left wondering which virus is causing your symptoms. Here’s what you need to know.

Flu season is starting to tick up in the U.S. And, looking at clues from other countries, we may be in for a rough winter.

But not all influenza is the same. And there are some notable differences between flu A and flu B strains.

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In particular, experts are concerned about a new flu variant of H3N2, a type of influenza A strain, called subclade K. This variant fueled an unusually severe flu season in Japan and tore through the U.K. and Canada before making its way here, experts told TODAY.com previously.

Last year's flu season was al

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