New variants and age shift to high fatality groups contribute to severe successive waves in the 2009 influenza pandemic in Taiwan
Journal
PLoS ONE
Journal Volume
6
Journal Issue
11
Pages
e28288
Date Issued
2011
Author(s)
Abstract
Past influenza pandemics have been characterized by the signature feature of multiple waves. However, the reasons for multiple waves in a pandemic are not understood. Successive waves in the 2009 influenza pandemic, with a sharp increase in hospitalized and fatal cases, occurred in Taiwan during the winter of 2010. In this study, we sought to discover possible contributors to the multiple waves in this influenza pandemic. We conducted a large-scale analysis of 4703 isolates in an unbiased manner to monitor the emergence, dominance and replacement of various variants. Based on the data from influenza surveillance and epidemic curves of each variant clade, we defined virologically and temporally distinct waves of the 2009 pandemic in Taiwan from May 2009 to April 2011 as waves 1 and 2, an interwave period and wave 3. Except for wave 3, each wave was dominated by one distinct variant. In wave 3, three variants emerged and co-circulated, and formed distinct phylogenetic clades, based on the hemagglutinin (HA) genes and other segments. The severity of influenza was represented as the case fatality ratio (CFR) in the hospitalized cases. The CFRs in waves 1 and 2, the interwave period and wave 3 were 6.4%, 5.1%, 15.2% and 9.8%, respectively. The results highlight the association of virus evolution and variable influenza severity. Further analysis revealed that the major affected groups were shifted in the waves to older individuals, who had higher age-specific CFRs. The successive pandemic waves create challenges for the strategic preparedness of health authorities and make the pandemic uncertain and variable. Our findings indicate that the emergence of new variants and age shift to high fatality groups might contribute potentially to the occurrence of successive severe pandemic waves and offer insights into the adjustment of national responses to mitigate influenza pandemics. ? 2011 Yang et al.
SDGs
Other Subjects
2009 H1N1 influenza; adolescent; adult; age; aged; article; child; cladistics; controlled study; disease severity; disease surveillance; fatality; genetic variability; human; infant; infection rate; major clinical study; phylogenetic tree; preschool child; real time polymerase chain reaction; reverse transcription polymerase chain reaction; seasonal variation; sequence analysis; Taiwan; virus culture
Publisher
Public Library of Science
Type
journal article