Analysis Of Influenza Epidemic Characteristics And Genetic Characteristics Of Influenza In Hubei Province From 2019 To 2022

Objective:Through the statistical analysis of the pathogenic surveillance data of influenza-like illness(ILI)in Hubei Province from 2019 to 2022,the epidemiological characteristics of influenza will be grasped,and molecular epidemiological studies on the HA and NA genes of influenza viruses in Hubei Province will be conducted to reveal the loci variation and molecular evolution patterns,which will provide an important basis for the prediction of influenza epidemic trends and the formulation of prevention and control strategies in the future.Methods:In the "China Influenza Surveillance Information System",we downloaded the surveillance data of influenza-like cases in Hubei Province from 2019 to 2022,built a database using Excel 2019 software,drew statistical tables,and conducted statistical analysis of ILI proportional pathogenic surveillance results by descriptive statistical analysis methods to grasp the epidemiological characteristics of influenza in Hubei Province in recent years.The representative influenza strains from 2019 to 2022 were selected for viral RNA extraction,PCR amplification and whole genome high-throughput sequencing,and the CLC Genomics Workbench(20.0.4)data analysis platform was used to splice the sequencing data to obtain the final sequences,and MEGA(Version 11.0)was used to Multiple sequence alignment was performed using MEGA(Version 11.0),and a phylogenetic tree was constructed for HA and NA genes using the Neighbor-Joining(NJ)method,while amino acid variants and drug resistance sites were analysed using a reference strain.Results:1.The influenza epidemic in Hubei Province from 2019 to 2022 showed a clear seasonal pattern,mainly concentrating on the winter and spring seasons,with peak influenza epidemics also occurring in summer in some years.2020 to 2021,the influenza epidemic was at a low level throughout the year,while the proportion of influenza-like cases gradually increased since 2021 and the level of influenza epidemic activity rose;from 2019 to 2022,influenza-like case outbreaks occur mainly in primary and secondary schools,mainly in winter and spring,with 75 outbreaks reported in December 2019,a significant increase in incidents.2.The age distribution of influenza-like cases varies,with the two age groups of 0to 4 years and 5 to 14 years being the main susceptible groups for influenza,with a composition of over 70%.3.From 2019 to 2022,the composition of each subtype of influenza viruses in Hubei Province will be different each year.In 2019,the epidemic type of influenza will be diversified,and the composition of the three dominant strains will be above30%,with the new A H1N1 strain dominating from weeks 1 to 11,the B Victoria strain dominating from weeks 12 to 20,and the A H3N2 strain dominating after week 43.In2020,there is only a short epidemic of H3N2 in January;in 2021,the epidemic type is single,with Victoria B being the dominant strain throughout the year;in 2022,the dominant strain is Victoria B and H3N2.4.The analysis of the genetic evolutionary tree of influenza viruses in Hubei Province from 2019 to 2022 shows that the evolutionary trees of the new influenza A H1N1 strains HA and NA are located in the Clade 6B major branch,which can be further divided into two major evolutionary clusters,Clade 6B.1A5 and Clade 6B.1A7,according to the specific mutations of the strains;the evolutionary trees of the influenza A H3N2 strains HA and NA belong to the 3C.2 The evolutionary tree of influenza A H3N2 strains HA and NA belong to the 3C.2a branch,which can be divided into 3C.2a1 b and 3C.2a1 b.2a.1 evolutionary clusters;the evolutionary tree of influenza B Victoria strains HA and NA are located in the V1 A.3 branch,which can be divided into V1 A.3a.1 and V1 A.3a.2 evolutionary clusters.5.Analysis of the HA antigenic determinants and receptor binding sites showed that the new influenza A(H1N1)strain had locus variants in the Sa and Sb antigenic determinants and in the receptor binding site at site 223;the influenza A(H3N2)strain had locus variants in three antigenic determinants and in the receptor binding site at sites 131,135,137 and 190;and the influenza B(Victoria)strain had locus variants in all four antigenic determinants.6.No mutations in known resistance sites of influenza strains were found in this study of NA gene resistance sites analysis of influenza virus strains in Hubei Province from 2019 to 2022.None of the new influenza A H1N1 strains in this study showed new potential glycosylation sites compared with the HA and NA proteins of the reference strains.Among the 34 HA strains of influenza A H3N2,12 strains lost one potential glycosylation site NGTS,4 strains added two potential glycosylation sites NWTG and NYTY;13 strains changed their glycosylation sites from NGTY to NETY due to the G484 E site variation;among the NA proteins of influenza A H3N2 strains,3strains were found to have an additional potential glycosylation site NDY due to the T329 S site variation.Among the HA proteins of 76 strains of influenza B Victorian strains,19 strains were found to have an additional potential glycosylation site,NETQ,due to the T195 N locus variation.Conclusions:1.Influenza-like cases in Hubei Province in 2019-2022 will mainly be high in winter and spring,with young people under 15 years of age and infants being the main susceptible groups to the influenza virus,suggesting the need to strengthen preventive and protective measures for this age group.2.The epidemiological pattern of different influenza virus subtypes varies,with seasonal influenza epidemics in 2019 characterised by epidemic type diversity and changing dominant strains.The predominant strains in 2021 and 2022 will be Victoria B and H3N2 respectively.3.The new influenza A H1N1,A H3N2 and B Victoria strains are constantly mutating and evolving into new branches;there are multiple site variations in the antigenic determinant cluster region of the HA protein and in the receptor binding site.4.No resistance site variation was found in this study,suggesting that neuraminidase inhibitors are effective in the current treatment of influenza viruses,but surveillance for resistance sites in influenza viruses in Hubei should be continuously strengthened.5.In this study,changes in potential glycosylation sites were found on the HA and NA proteins of H3N2 and on the HA protein of the Victoria B strain,suggesting that influenza viruses are mutating and at the same time enhancing their adaptability to the host.