title: Reduced replication capacity of influenza A(H1N1)pdm09 virus during the 2010-2011 winter season in Tottori, Japan.
abstract: A novel swine-origin influenza A(H1N1)pdm09 virus has been circulating in humans since March-April, 2009. The 2009-2010 epidemic involved predominantly a single subtype of A(H1N1)pdm09 (at 96%, 46/48) in the sentinel sites of this study. However, A(H1N1)pdm09 started to circulate together with other type/subtype (49%, 33/68) at the first peak in the next epidemic season in 2010-2011: A(H1N1)pdm09/A(H3N2) (9%, 6/68), A(H1N1)pdm09/B (35%, 24/68), and A(H1N1)pdm09/A(H3N2)/B (4%, 3/68). Single infection of A(H1N1)pdm09 became a rare event (8%, 5/65) at the second peak of the same season in 2010-2011 compared with that at the first peak (50%, 34/68). Concurrently with this decline, single infections of others, A(H3N2) or B, became evident (6%, 4/65; 14%, 9/65, respectively). Triple infections were more common (29%, 19/65) at the second peak than at the first peak (4%). The A(H1N1)pdm09 detected in 2010-2011 produced less virus upon 72 hr of incubation in vitro after the inoculations at 10(4) and 3,300 copies/ml (2.3 × 10(9) and 2.3 × 10(9) copies/ml on average) than that in 2009-2010 (3.7 × 10(9) and 1.3 × 10(10) copies/ml on average; P<0.05 by ANOVA test), respectively. As described above, the replication capacity of A(H1N1)pdm09 seems to have deteriorated in the 2010-2011 season presumably due to substantial herd immunity and allowed the existence of other type/subtype. These results suggest that assessment of replication capacity is indispensable for analysis of influenza epidemics.
authors: Division of Virology, Department of Microbiology and Immunology, Tottori University Faculty of Medicine, Yonago City, Japan.
authors: Akeno
authors: A
authors: Tsuneki
authors: Asao
authors: A
authors: Itagaki
authors: Hideaki
authors: H
authors: Tsuchie
authors: Misato
authors: M
authors: Tokuhara
authors: Takayoshi
authors: T
authors: Okada
authors: Sakae
authors: S
authors: Narai
authors: Masaaki
authors: M
authors: Kasagi
authors: Kiyoshi
authors: K
authors: Tanaka
authors: Seiji
authors: S
authors: Kageyama
mesh_terms: D060085:Coinfection / Q000453:epidemiology / Q000821:virology; D006801:Humans; D053118:Influenza A Virus, H1N1 Subtype / Q000302:isolation & purification* / Q000502:physiology*; D053122:Influenza A Virus, H3N2 Subtype / Q000302:isolation & purification; D009981:Influenza B virus / Q000302:isolation & purification; D007251:Influenza, Human / Q000453:epidemiology* / Q000821:virology*; D007564:Japan / Q000453:epidemiology; D008969:Molecular Sequence Data; D012367:RNA, Viral / Q000235:genetics; D012621:Seasons; D017422:Sequence Analysis, DNA; D014779:Virus Replication
chemical_list: D012367:RNA, Viral
keywords: A(H3N2); B; RNA levels; co-circulations; surveillance