H3N2 is a subtype of influenza A virus is a major cause of seasonal influenza epidemics.
The designation refers to the specific combination of surface proteins on the virus: hemagglutinin type 3 (H3) and neuraminidase type 2 (N2).
H3N2 currently co-circulates globally with influenza A(H1N1)pdm09 and influenza B viruses as part of seasonal influenza.
Among these circulating strains, H3N2 is historically associated with more severe disease, particularly higher rates of hospitalization and mortality in adults aged 65 years and older.
The virus undergoes continuous genetic and antigenic evolution- antigenic drift, which involves the accumulation of mutations in its surface proteins.
This rapid evolution necessitates frequent updates to vaccine strains and contributes to the characteristically lower vaccine effectiveness against H3N2 compared to other influenza subtypes.
H3N2 is associated with more severe flu seasons than H1N1 or influenza B viruses.
Dysproportionately affects the oldest and youngest individuals and leads to a greater disease burden that a typical flu season.
Recent surveillance has identified H3N2 subclade K, which has accumulated approximately 10 additional mutations in the hemagglutinin gene compared to earlier strains.
H3N2 viruses also circulate in animal populations, particularly pigs and poultry.
The primary public health concern of H3N2 virus relates to human seasonal influenza strains that have adapted for efficient human-to-human transmission.