| ObjectivesBased on the features of common susceptibility to influenza,rapid evolution of influenza virus,low protection rate of vaccine,and frequently emergence antiviral resistance strains,it is particularly important to strengthen the epidemiological and virological surveillance of influenza.In this study,the data of influenza-like illness(ILI)and virological surveillance were analyzed,in order to explore the epidemiological characteristics and the predominant subtypes/lineages in Guangdong from 2019 to 2021.The whole genome sequences of some Bv strains during 2019-2022 were obtained by sequencing,then the molecular characteristics and genetic evolution were analyzed,which benefited to prevent and control for influenza in Guangdong.Methods1.The data of ILI and virological surveillance in the national sentinel hospitals/units in Guangdong during 2019-2021 were collected from the Guangdong Influenza Surveillance Network.A descriptive epidemiological approach was conducted by χ2 test in this study.2.Based on the spatial and temporal sampling,77 of Bv strains were identified and sequenced in Guangdong from 2019 to 2022.The whole genome sequences of Bv strains were sequenced by Sanger sequencing and Next-generation sequencing(NGS),the molecular evolution of Bv strains was analyzed by performing multiple sequence alignment and constructing evolutionary tree,etc.Results1.The positive rate of influenza virus was 8.55%(7699/90049)in Guangdong from 2019 to 2021,and the annual positive rate showed "V" type change,among which the positive rate of IAV decreased year by year till zero in 2021,while the annual positive rate of Bv also showed a "V" type.The predominant subtypes/lineages varied every year.Three of H1N1pdm,H3N2 and Bv were jointly prevalent in 2019,while H3N2 and Bv lineage were dominantly circulated in 2020 and 2021,respectively.2.In terms of age distribution of the patients infected with influenza virus,the age groups infected with H1N1pdm were older than those infected with H3N2,and the patients infected with Bv showed two peaks in 5～14 age-group(7.61%)and 25～34 age-group(6.13%).3.In this study,Bv was shared by three evolutionary clades.Specifically,the result of HA sequences analysis showed that the Bv strains during 2019-2020 clustered in Clade V1A.3,the first half of 2021 strains were classified into Clade V1A.3a.1,and the second half of 2021 and the 2022 ones mainly belonged to CladeⅥA.3a.2(86.36%,38/44).4.A total of 16 amino acid mutations were emerged in 4 epitopes,of which 7 mutations occurred in 120 loop.There was not any known mutation of antiviral susceptibility.There were the highest variation rates of amino acid in the eight gene segments in 2021,with 6.74%in NS1,4.46%in HA and 4.28%in NA.A total of involving three potential glycosylation sites lost in NS1 of 22 strains,meanwhile 17 strains and 1 strain added one potential glycosylation site in HA and NA,respectively.Conclusions1.The annual positive rate of influenza virus in Guangdong showed a "V" type,with a decrease of positive rate of IAV year by year to zero in 2021,while the annual positive rate of Bv showed a "V" shape,and only Bv lineage was detectable in 2021.Each subtype/lineage showed different epidemiological characteristics and varied in risks of infected population.2.In this study,three clades of Bv circulated jointly with increasing genetic diversity.There were 16 mutation sites involving 4 epitopes of HA1 region,which suggested that the matching between the epidemic strain and vaccine to update the vaccine strain would be paid attention to.The Guangdong strains continued to be susceptible to antiviral drugs.The degrees of variation in HA,NA and NS1 were higher than those in other segments. |
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