H3N2 Influenza Virus: Is it Pandemic?

The H3N2 subtype evolved from H2N2 virus and caused the pandemic in 1968-69 in Hong Kong. A total of 293 patients with influenza like illness were investigated during the course of continuous surveillance on influenza in Pune, India in 2000. The throat/nasal swab specimens collected from these patients were inoculated in MDCK cell culture and influenza types A(H3N2), A(H1N1) and type B strains were isolated. They were identified as similar to the recently prevalent variant strains; A/Sydney/05/97(H3N2), A/New Caledonia/20/99(H1N1) and B/Sichuan/379/99. The latter two were the new variant strains reported for the first time in Pune. It is important to note that A(H1N1) strains were isolated in Pune during 2000 after a gap of 10 years. Since then, H3N2 influenza viruses have rapidly evolved and been the prominent strain in the influenza season, except the Covid pandemic period. Influenza B viruses are classified into lineages. At present, either B/Yamagata or B/Victoria viruses are in circulation. Therefore, unlike Covid, which was first identified in 2019, H3N2 has existed for several decades. Another major difference is that while Covid was caused by SARS CoV-2 virus, H3N2 is a subtype of influenza virus.