A survey of levels of antibodies against influenza viruses in the population of Wuxi City / 中华实验和临床病毒学杂志

<p><b>OBJECTIVE</b>To investigate levels of antibodies against type A and type C influenza viruses and those against the 2009 H1N1 influenza A virus (before and after the 2009 H1N1 pandemic) among residents in Wuxi. To compare levels of antibodies against the 2009 H1N1 influenza virus (one year after the pandemic) in the unvaccinated population with those in the population who received vaccine.</p><p><b>METHODS</b>Serum samples were collected from subjects (aged 1-60 years) during September 2008 to May 2009, and during September 2010 to January 2011. Also collected were serum samples from adults who had received vaccines for pandemic (H1N1) 2009 for one year. Antibody response to influenza viruses was measured using hemagglutination inhibition (HI) assay. Seropositivity rate, seroprotection rate and geometric mean titer (GMT) were compared for each age group during different periods.</p><p><b>RESULTS</b>Before the outbreak of the 2009 H1N1 pandemic, seropositivity rate, seroprotection rate and GMT among the study subjects in were 2.86% (4/140), 0.71% (1/140) and 5.23, respectively. One year after the outbreak, seropositivity rate, seroprotection rate and GMT among the study subjects were 66.33%, 37.76% and 19.17, respectively. Among them, adult subjects showed 50.00% seropositivity rate, 19.44% seroprotection rate and 13.09 GMT, while adult subjects who had received vaccine for one year showed 61.36% seropositivity rate, 22.73% seroprotection rate and 14.14 GMT. No significant difference was observed between these two populations (P > 0.05 for all three indexes). Furthermore, before the outbreak of the 2009 H1N1 pandemic, levels of antibodies against seasonal influenza viruses among the study subjects were as follows: for H1N1 virus, seropositivity rate, seroprotection rate and GMT were 55.00%, 35.00% and 16.90, respectively; for H3N2 virus, seropositivity rate, seroprotection rate and GMT were 86.40%, 84.30% and 58.56, respectively.</p><p><b>CONCLUSION</b>One year after the 2009 H1N1 influenza A virus had spread to Wuxi, the population levels of antibodies against this virus have approached those against seasonal influenza viruses, as reflected by seropositivity rates, seroproection rates and GMT. Moreover, considerable levels of antibodies against seasonal influenza viruses were observed in populations, indicating no seasonal influenza outbreak would occur recently.</p>

Etiology monitoring of influenza virus and variation in hemagglutinin genes of H13 subtype in Wuxi area / 中华实验和临床病毒学杂志

<p><b>OBJECTIVE</b>To monitor the seasonal distribution of influenza types and subtypes in Wuxi area during 2005-2008, and to investigate the variation in hemagglutinin (HA) genes of A/H3N2 strains in 2008.</p><p><b>METHODS</b>Nose-throat swab specimens were collected in Wuxi area from flu-like patients from outpatient departments of hospitals as well as from clustering flu-like outbreak patients from workspace, followed by MDCK cell inoculation. Types and subtypes of positive influenza isolates were identified using standard antiserum. We then sequenced the HA genes for H3 subtype influenza viruses isolated from 2008 specimens to investigate the variation in HA genes.</p><p><b>RESULTS</b>During 2005 and September 2008, 435 strains of influenza viruses were isolated from flu-like patients in Wuxi Area, among which 164 isolates are of A/H1N1 subtype, 80 isolates are of A/H3N2 subtype, and 191 isolates are of B type. These types/subtypes have significant seasonal distributions. Sequences of HA genes for H3 subtype show that the 9 strains isolated in Wuxi area are similar to those of strains isolated in Shanghai within the same period. Many of the sequences belong to the same branch of the phylogenetic tree, and are similar to sequences of vaccine strains in WHO 2008-2009 repositories.</p><p><b>CONCLUSION</b>A/H1N1, A/H3N2 and B still attribute to most of the sporadic and local outbreaks of influenza infection in Wuxi area in recent years. HA genes of A/H3N2 strains isolated in Wuxi area are similar to those of strains isolated in Shanghai in the same period, and also similar to those of vaccine strains recommended by WHO for 2008-2009.</p>