CONCISE COMMUNICATION Intercontinental Circulation of Human Influenza A(H1N2) Reassortant Viruses during the 2001–2002 Influenza Season

influenza season. The HAs of these H1N2 viruses were similar to that of the A/New Caledonia/ 20/99(H1N1) vaccine strain both antigenically and genetically, and the NAs were antigenically and genetically related to those of recent human H3N2 reference strains, such as A/Moscow/ 10/99(H3N2). All 6 internal genes of the H1N2 reassortants examined originated from anH3N2 virus. This article documents the first widespread circulation of H1N2 reassortants on 4 con-tinents. The current influenza vaccine is expected to provide good protection against H1N2 viruses, because it contains the A/New Caledonia/20/99(H1N1) and A/Moscow/10/99(H3N2)-like viruses, which have H1 and N2 antigens that are similar to those of recent H1N2 viruses. Since their reappearance in 1977, influenza A(H1N1) viruses have caused disease primarily in children and young adults and have continued to circulate in humans, along with influenza A(H3N2) viruses. The cocirculation of these 2 subtypes of hu-man influenza A viruses provides an opportunity for genetic reassortment to occur between the types during mixed infection in an individual with both viruses. Such genetic reassortant