Mexico flags first case of fast-spreading H3N2 ‘subclade K’ Flu

Mexico has confirmed its first case of influenza A(H3N2) subclade K, a fast-spreading strain now driving early flu seasons in Europe and North America.

The Mexican Ministry of Health said the case was detected by the National Institute of Respiratory Diseases and that the patient has recovered after antiviral treatment. It stressed the virus “does not represent a reason for alarm for the population.” The location of the first case was not disclosed.

The announcement is significant because subclade K has become the dominant H3N2 strain in several regions. The Pan American Health Organization (PAHO) and the World Health Organization (WHO) warned on Thursday that its rapid spread could lead to an earlier and heavier flu season across the Americas.

In a joint statement, PAHO and WHO said that “no significant change in clinical severity has been documented so far” but pointed out that H3N2-dominated seasons are often linked to higher hospitalisations, particularly among older adults.

Health authorities urged people to take preventative measures and reiterated that vaccination remains the main defence against influenza, COVID-19 and pneumococcal disease.

“Despite the antigenic differences observed in the A(H3N2) subclade K, preliminary vaccine effectiveness data show that protection against hospitalisations remains at levels similar to previous seasons (≈70–75% in children and 30–40% in adults),” added PAHO and WHO.