Epidemiological and virological surveillance of influenza viruses in China during 2020–2021

Background: During the coronavirus disease 2019(COVID-19)pandemic,seasonal influenza activity declined globally and remained below previous seasonal levels,but intensified in China since 2021.Preventive measures to COVID-19 accompanied by different epidemic characteristics of influenza in different regions of the world.To better respond to influenza outbreaks under the COVID-19 pandemic,we analyzed the epidemiology,antigenic and genetic characteristics,and antiviral susceptibility of influenza viruses in the mainland of China during 2020–2021.Methods: Respiratory specimens from influenza like illness cases were collected by sentinel hospitals and sent to network laboratories in Chinese National Influenza Surveillance Network.Antigenic mutation analysis of influenza virus isolates was performed by hemagglutination inhibition assay.Next-generation sequencing was used for genetic analyses.We also conducted molecular characterization and phylogenetic analysis of circulating influenza viruses.Viruses were tested for resistance to antiviral medications using phenotypic and/or sequence-based methods.Results: In the mainland of China,influenza activity recovered in 2021 compared with that in 2020 and intensified during the traditional influenza winter season,but it did not exceed the peak in previous years.Almost all viruses isolated during the study period were of the B/Victoria lineage and were characterized by genetic diversity,with the subgroup 1A.3a.2 viruses currently predominated.37.8%viruses tested were antigenically similar to reference viruses representing the components of the vaccine for the 2020–2021 and 2021–2022 Northern Hemisphere influenza seasons.In addition,China has a unique subgroup of 1A.3a.1 viruses.All viruses tested were sensitive to neuraminidase inhibitors and endonuclease inhibitors,except two B/Victoria lineage viruses identified to have reduced sensitivity to neuraminidase inhibitors.Conclusions: Influenza activity increased in the mainland of China in 2021,and caused flu season in the winter of 2021–2022.Although the diversity of influenza(sub)type decreases,B/Victoria lineage viruses show increased genetic and antigenic diversity.The world needs to be fully prepared for the co-epidemic of influenza and severe acute respiratory syndrome coronavirus 2(SARS-CoV-2)virus globally.

Distribution of avian influenza viruses according to environmental surveillanee during 2014-2018, China

Background:Recurrent infections of animal hosts with avian influenza viruses(AIVs)have posted a persistent threat.It is very important to understand the avian influenza virus distribution and characteristics in environment associated with poultry and wild bird.The aim of this study was to analyze the geographic and seasonal distributions of AIVs in the 31 provinces,municipalities and autonomous region(PMA)of China,compare the AIVs prevalence in different col-lecting sites and sampling types,analyze the diversity of AIVs subtypes in environment.

Epidemiological characteristics of imported respiratory infectious diseases in China,2014-2018

Background:With the progress of globalization,international mobility increases,greatly facilitating cross-border transmission of respiratory infectious diseases(RIDs).This study aimed to analyze the epidemiological characteristics and factors influencing imported RIDs,with the goal of providing evidence to support adoption of high-tech,intel-ligent methods to early find imported RIDs and prevent their spread in China.Methods:We obtained data of imported RIDs cases from 2014 to 2018 from the Inbound Sentinel Network of Customs and the National Notifiable Diseases Reporting System in China.We analyzed spatial,temporal,and population distribution characteristics of the imported RIDs.We developed an index to describe seasonality.Pearson correlation coefficients were used to examine associations between independent variables and imported cases.Data analyses and visualizations were conducted with R software.Results:From a total of 1409265253 inbound travelers,31732(2.25/100000)imported RIDs cases were reported.RIDs cases were imported from 142 countries and five continents.The incidence of imported RIDs was nearly 5 times higher in 2018(2.81/100000)than in 2014(0.58/100000).Among foreigners,incidence rates were higher among males(5.32/100000),0–14-year-olds(15.15/100000),and cases originating in Oceania(11.10/100000).The vast majority(90.3%)of imported RIDs were influenza,with seasonality consistent with annual seasonality of influenza.The spatial distribution of imported RIDs was different between Chinese citizens and foreigners.Increases in inbound travel volume and the number of influenza cases in source countries were associated with the number of imported RIDs.Conclusions:Our study documented importation of RIDs into China from 142 countries.Inbound travel poses a significant risks bringing important RIDs to China.It is urgent to strengthen surveillance at customs of inbound travelers and establish an intelligent surveillance and early warning system to prevent importation of RIDs to China for preventing further spread within China.

Detection of reassortant avian influenza A (H11N9) virus in environmental samples from live poultry markets in China

Background:Avian influenza viruses have caused human infection and posed the pandemic potential.Live poultry markets are considered as a source of human infection with avian influenza viruses.Avian influenza routine surveillance of live poultry markets is taken annually in China.We isolated the 2 H11N9 influenza virus from the surveillance program.To better understand the risk caused by these new viruses,we characterize the genetic and pathogenicity of the two viruses.Methods:Viral isolation was conducted with specific pathogen-free(SPF)embryonated chicken eggs.Whole genome was sequenced,and phylogenetic analysis was conducted.Results:Two H11N9 viruses were identified,with all 8 segments belonging to the Eurasian lineage.The HA,NA,M,NS and PA genes were similar to virus isolates from ducks,and the NP,PB2 and PB1 gene segments were most similar to those viruses from wild birds,indicating that the H11N9 viruses might represent reassortant viruses from poultry and wild birds.The HA receptor binding preference was avian-like,and the cleavage site sequence of HA showed low pathogenic.The NA gene showed 94.6%identity with the novel H7N9 virus that emerged in 2013.There was no drug resistance mutation in the M2 protein.The Asn30Asp and Thr215Ala substitutions in the M1 protein implied a potentially increased pathogenicity in mice.Both viruses were low-pathogenic strains,as assessed by the standards of intravenous pathogenicity index(IVPI)tests.Conclusion:Two reassortant H11N9 avian influenza viruses were detected.These viruses showed low pathogenicity to chickens in the IVPI test.Public health concern caused by the reassortant H11N9 viruses should be emphasized during the future surveillance.