Virological characterization of influenza H1N1pdm09 in Vietnam, 2010‐2013

Abstract

ObjectivesInfluenza A/H1N1pdm09 virus was first detected in Vietnam on May 31, 2009, and continues to circulate in Vietnam as a seasonal influenza virus. This study has monitored genotypic and phenotypic changes in this group of viruses during 2010–2013 period.Design and settingWe sequenced hemagglutinin (HA) and neuraminidase (NA) genes from representative influenza A/H1N1pdm09 and compared with vaccine strain A/California/07/09 and other contemporary isolates from neighboring countries. Hemagglutination inhibition (HI) and neuraminidase inhibition (NAI) assays also were performed on these isolates.SampleRepresentative influenza A/H1N1pdm09 isolates (n = 61) from ILI and SARI surveillances in northern Vietnam between 2010 and 2013.Main outcome measures and resultsThe HA and NA phylogenies revealed six and seven groups, respectively. Five isolates (8·2%) had substitutions G155E and N156K in the HA, which were associated with reduced HI titers by antiserum raised against the vaccine virus A/California/07/2009. One isolate from 2011 and one isolate from 2013 had a predicted H275Y substitution in the neuraminidase molecule, which was associated with reduced susceptibility to oseltamivir in a NAI assay. We also identified a D222N change in the HA of a virus isolated from a fatal case in 2013.ConclusionsSignificant genotypic and phenotypic changes in A/ H1N1pdm09 influenza viruses were detected by the National Influenza Surveillance System (NISS) in Vietnam between 2010 and 2013 highlighting the value of this system to Vietnam and to the region. Sustained NISS and continued virological monitoring of seasonal influenza viruses are required for vaccine policy development in Vietnam. 3

Surveillance of Severe Acute Respiratory Infection (SARI) for Hospitalized Patients in Northern Vietnam, 2011–2014

“…Among the determined influenza type and subtype viruses, influenza A H1pdm09 was the major virus associated with hospitalization for SARI (221 313; 70.6 of all influenza cases). This finding is supported by NISS data from the study period, in which influenza A H1pdm09 was presented and predominated in 2011, 2013, and 2014, while A H3 occurred in 2012 and early 2014 (14). In our study, A H3 was detected in 11.6 of cases.…”

“…1), while ILI incidence peaked twice per year in 2009-2013 period (14). An overlap in high SARI occurrence and high ILI occurrence in February and March was observed, indicating that increased ILI activity did not cause SARI hospitalization (Fig.…”

“…The World Health Organization estimated that 20 of hospitalizations among children ＜ 5 years was attributable to SARI (14). Many studies of viral respiratory infections have shown higher viral detection rates among children than among adults (11)(12)(13)15,16), underlying the importance of continued monitoring of SARI in young age groups to detect respiratory viral outbreaks.…”

Genetic and antigenic characterization of influenza A(H1N1)pdm09 in Yantai, China, during the 2009–2017 influenza season

“…After the pandemic in 2009/2010, A(H1N1)pdm09 became a fluctuant epidemic: A(H1N1)pdm09 prevailed for two years and then receded from dominance for a year. The results were consistent with those obtained by other researchers . The reason for the recurrent epidemics of A(H1N1)pdm09 was that the gradual accumulation of genetic changes and altered antigenicity enabled the viruses to evade host immune responses …”

“…During the seven flu seasons since its emergence, the A(H1N1)pdm09 virus underwent substantial genetic and antigenic changes that divided it into eight genetic groups and several subgroups . Phylogenetic analyses of the A(H1N1)pdm09 virus HA and NA genes isolated from Yantai during the study period indicated that the viruses mostly clustered in chronological order on the phylogenetic trees and that most Yantai strains were grouped into genetic clades 1.7, 6C, 6B.1 and 6B.2, which were similar to those circulating worldwide …”