Flu by state: Where this season’s highly contagious variant is spreading the most

A new form of the flu, which is highly contagious and aggressive, is sweeping the nation this season.

A mutation of influenza A H3N2, called subclade K, has been detected as the culprit in rising global cases, including in the U.S.

The World Health Organization stated on its website that the K variant marks "a notable evolution in influenza A (H3N2) viruses," which some say calls into question the effectiveness of this season's influenza vaccine against the strain.

‘AGGRESSIVE’...