The rapid evolution of influenza A(H3N2) viruses necessitates close monitoring of their antigenic properties so the emergence and spread of antigenic drift variants can be rapidly identified. Changes in hemagglutinin (HA) acquired by contemporary A(H3N2) viruses hinder antigenic characterization by traditional methods, thus complicating vaccine strain selection. Sequence-based approaches have been used to infer virus antigenicity; however, they are time consuming and midthroughput. To facilitate virological surveillance and epidemiological studies, we developed and validated a pyrosequencing approach that enables identification of six HA clades of contemporary A(H3N2) viruses. The identification scheme of viruses of the H3 clades 3C.2, 3C.2a, 3C.2b, 3C.3, 3C.3a, and 3C.3b is based on the interrogation of five single nucleotide polymorphisms (SNPs) within three neighboring HA regions, namely 412 to 431, 465 to 481, and 559 to 571. Two bioinformatics tools, IdentiFire (Qiagen) and FireComb (developed in-house), were utilized to expedite pyrosequencing data analysis. The assay's analytical sensitivity was 10 focus forming units, and respiratory specimens with threshold cycle (C T ) values of Ͻ34 typically produced good quality pyrograms. When applied to 120 A(H3N2) virus isolates and 27 respiratory specimens, the assay displayed 100% agreement with clades determined by HA sequencing coupled with phylogenetics. The multi-SNP analysis described here was readily adopted by another laboratory with pyrosequencing capabilities. The implementation of this approach enhanced the findings from virological surveillance and epidemiological studies between 2013 and 2016, which examined more than 3,000 A(H3N2) viruses.KEYWORDS A(H3N2), genotyping, influenza, pyrosequencing S ince their introduction into the human population in 1968, influenza A(H3N2) viruses have been responsible for seasonal epidemics and associated with both a prolonged duration of the epidemic season and a greater disease severity (1-4). The hemagglutinin (HA) glycoprotein is the major surface antigen of influenza viruses; it is also responsible for the receptor binding and membrane fusion required for entrance into susceptible host cells (5). Decades ago, this glycoprotein was named "hemagglutinin" for its ability to bind and bridge erythrocytes. The other surface antigen, neuraminidase (NA), is a receptor-destroying enzyme (6). As with other seasonal influenza viruses, A(H3N2) viruses undergo genetic and antigenic changes, called antigenic drift,