Influenza B virus (IBV) is more likely to cause complications than influenza A virus (IAV) and even causes higher disease burden than IAV in a certain season, but IBV has received less attention. In order to analyze the genetic evolution characteristics of the clinical strain IBV (B/Guangxi-Jiangzhou/1352/2018), we constructed genetic evolution trees and analyzed the homology and different amino acids of hemagglutinin and neuraminidase referring to the vaccine strains recommended by World Health Organization (WHO). We found that strain B/Guangxi-Jiangzhou/1352/2018 was free of interlineage reassortment and poorly matched with the vaccine strain B/Colorado/06/2017 of the same year. We also determined the median lethal dose (LD₅₀) and the pathogenicity of strain B/Guangxi-Jiangzhou/1352/2018 in mice. The results showed that the LD₅₀ was 10^5.9 TCID₅₀ (median tissue culture infective dose), the IBV titer in the lungs reached peak 1 d post infection and the mRNA level of the most of inflammatory cytokines in the lungs reached peak 12 h post infection. The alveoli in the lungs were severely damaged and a large number of inflammatory cells were infiltrated post infection. The study demonstrated that the clinical strain IBV (B/Guangxi-Jiangzhou/1352/2018) could infect mice and induce typical lung inflammation. This will facilitate the research on the pathogenesis and transmission mechanism of IBV, and provide an ideal animal model for evaluation of new vaccines, antiviral and anti-inflammatory drug.
Amino Acids/genetics* ; Animals ; Antiviral Agents/pharmacology* ; China ; Cytokines/metabolism* ; Hemagglutinins/metabolism* ; Humans ; Influenza B virus/pathogenicity* ; Influenza, Human/virology* ; Mice ; Neuraminidase/genetics* ; Orthomyxoviridae Infections/virology* ; Phylogeny ; RNA, Messenger/metabolism* ; Virulence/genetics*

Nonpharmaceutical interventions (NPIs) have been commonly deployed to prevent and control the spread of the coronavirus disease 2019 (COVID-19), resulting in a worldwide decline in influenza prevalence. However, the influenza risk in China warrants cautious assessment. We conducted a cross-sectional, seroepidemiological study in Shandong Province, Northern China in mid-2021. Hemagglutination inhibition was performed to test antibodies against four influenza vaccine strains. A combination of descriptive and meta-analyses was adopted to compare the seroprevalence of influenza antibodies before and during the COVID-19 pandemic. The overall seroprevalence values against A/H1N1pdm09, A/H3N2, B/Victoria, and B/Yamagata were 17.8% (95% CI 16.2%-19.5%), 23.5% (95% CI 21.7%-25.4%), 7.6% (95% CI 6.6%-8.7%), and 15.0 (95% CI 13.5%-16.5%), respectively, in the study period. The overall vaccination rate was extremely low (2.6%). Our results revealed that antibody titers in vaccinated participants were significantly higher than those in unvaccinated individuals (P < 0.001). Notably, the meta-analysis showed that antibodies against A/H1N1pdm09 and A/H3N2 were significantly low in adults after the COVID-19 pandemic (P < 0.01). Increasing vaccination rates and maintaining NPIs are recommended to prevent an elevated influenza risk in China.

Objective:To analyze the antigenicity and genetic characteristics of two strains of Eurasian avian H1N1 swine influenza virus (EAS-H1N1) isolated from 2 human cases found in Gansu province to provide scientific reference for disease prevention and control.Methods:Two cases of human infection with EAS-H1N1 discovered in Gansu province since February 2021 were analyzed for antigenicity and genome comparison, and their genome characteristics were analyzed using software such as Mega7.0.Results:Two human infections with EAS-H1N1 had related environmental exposure history. Two strains were obtained: A/Gansu-Xifeng/1143/2021 and A/Gansu-Xifeng/1194/2021. The two strains of HA, NA genes were all from the Eurasian avian H1N1 swine influenza virus, and are closely related to the human infection EAS-H1N1 virus in Hebei and Tianjin and the EAS-H1N1 virus isolated from the mink in Shandong; the HA receptor binding sites of 2 strains E190D and D225E mutations occurred in all spots, and there were no H274Y and N294S mutations in NA protein.Conclusions:Some important molecular mutations occurred in the genome of people infected with EAS-H1N1 virus in Gansu province, which may lead to increased virulence and potential human-to-human transmission. Strengthening the research and analysis of EAS-H1N1 gene characteristics will help to monitor the mutation and mutation of the virus at the molecular level and scientifically prevent and control the epidemic.

Objective:To understand the agglutination characteristics of different subtypes of avian influenza viruses, we selected erythrocytes from different sources to find suitable erythrocytes for influenza environmental sample detection.Methods:Different subtypes of avian influenza viruses, which were isolated from environmental sample between 2009 and 2016 in China, were selected to do hemagglutination assay using 5 animal erythrocytes (chicken, turkey, guinea pig, horse, and sheep). Flow cytometry was used to detect expression level and type of sialic acid receptors of different erythrocytes, and the characteristics of the receptor binding domain (RBD) of the viral hemagglutinin protein were analyzed by amino acid sequence.Results:In this study, a total of 28 strains of avian influenza virus including 14 subtypes were detected. The result showed that all viruses could agglutinate with turkey and guinea pig erythrocytes and the rest three erythrocytes were unable to produce agglutination with some viruses; among them, one H9N2 virus (A/environment/Anhui/43762/2015) did not agglutinate with chicken erythrocytes, one H1N1 virus (A/environment/Shandong/76972/2014) and two H9N2 viruses (A/environment/Chongqing/79449/2014 and A/environment/Anhui/43762/2015) did not agglutinate with horse erythrocytes, two viruses of H9N2 (A/environment/Chongqing/79449/2014 and A/environment/Anhui/43762/2015) and two viruses of H13N8 (A/environment/Qinghai Lake/166/2012 and A/environment/Qinghai Lake/13/2012) did not agglutinate with sheep erythrocytes. The result of flow cytometry showed that two sialic acid receptors, α-2, 3 and α-2, 6, were detected on the surface of erythrocytes of turkey, chicken and guinea pig, but the expression ratios of the two receptors were different. Only the expression of α-2, 3 sialic acid receptors was detected in horse and sheep erythrocytes. Sequence analysis suggested that amino acid substitution in key regions of viral hemagglutinin protein RBD may be an important factor affecting the binding properties of different erythrocytes.Conclusions:Our result suggested that turkey and guinea pig erythrocytes are the most sensitive in the hemagglutination test. Receptor expression and type of erythrocytes from different sources can significantly affect the agglutination reaction of different subtypes of avian influenza virus, and the amino acid changes in key regions of RBD can also affect the result of agglutination reaction.

Objective:The antigenic and genetic characteristics of influenza A(H1N1)pdm09 virus isolated from the mainland of China during the 2018-2019 influenza surveillance year were analyzed.Methods:Two thousand nine hundred and fifty-eight influenza A(H1N1)pdm09 virus strains in the 2018-2019 influenza surveillance year were analyzed by hemagglutination inhibition test. The hemagglutinin(HA) gene of 279 influenza A(H1N1)pdm09 virus strains was sequenced and analyzed. The representative strains of the dominant clades were performed for antigenic characteristics using post-vaccination human antisera.Results:Two thousand eight hundred and sixty-one (97%, 2 861/2 958) viruses characterized were antigenically similar to A/Michigan/45/2015. All HA gene of the sequenced viruses belonged to 6B.1 clade, and 269(96%, 269/279) viruses belonged to 6B.1A subclade. Compared with the vaccine virus, it had the common amino acid substitutions of S74R, S164T and I295V in the HA protein. There were several small groups with common amino acid substitutions in the 6B.1A subclade, and 51% sequenced viruses had S183P amino acid substitution in this subclade. The result of antigenic analysis using post-vaccination human antiserums showed that most of the representative strains were well inhibited by the sera.Conclusions:The antigenicity of influenza A(H1N1)pdm09 viruses in the mainland of China in 2018-2019 influenza surveillance year matched well with the corresponding vaccine strain, but the HA gene had genetically diverse characteristic.

Objective: To analyze epidemiological characteristics of influenza-like illness outbreaks in mainland China during 2017-2018 surveillance season, and to provide scientific evidence for developing influenza prevention and control strategies. Methods: We collected the data on reported influenza outbreaks in 2017-2018 surveillance season from China Influenza Surveillance Information System and China Public Health Emergency Management Information System and analyzed the data of laboratory-confirmed influenza-like illness outbreaks by descriptive epidemiological methods. Results: During the surveillance season, a total of 2 398 influenza-like illness outbreaks (with 10 or more incidences in an outbreak) in mainland China were reported, involving 87 084 patients, of which 2 323 were influenza outbreaks, involving 85 531 patients. The reported influenza-like illness outbreaks occurred most frequently from November 2017 to January 2018 in both the southern and northern regions and the highest peaks were in December 2017. During the period 1 850 influenza-like illness outbreaks (77.15%) were reported in the southern region, and 548 influenza-like illness outbreaks (22.85%) were reported in the northern region. The most of the outbreaks occurred in primary, secondary schools and nursery care schools, with a total of 2 210 reports (92.16%). And the majority of the outbreaks involved 10-29 incident cases. The dominant isolated virus strains for the outbreaks were influenza B (1 505 outbreaks, 62.76% of all the outbreaks). Conclusion Seasonality of influenza outbreaks were observed in mainland China during 2017-2018 surveillance season and the reported influenza outbreaks were most frequently occurred in autumn-winter season and in southern China. Primary, secondary schools and nursery care schools are high-risk places for outbreaks, and the dominant isolated virus strains for the outbreaks were influenza B.

Objective To analyze epidemiological characteristics of influenza?like illness outbreaks in mainland China during 2017-2018 surveillance season, and to provide scientific evidence for developing influenza prevention and control strategies. Methods We collected the data on reported influenza outbreaks in 2017-2018 surveillance season from China Influenza Surveillance Information System and China Public Health Emergency Management Information System and analyzed the data of laboratory?confirmed influenza?like illness outbreaks by descriptive epidemiological methods. Results During the surveillance season, a total of 2 398 influenza?like illness outbreaks (with 10 or more incidences in an outbreak) in mainland China were reported, involving 87 084 patients, of which 2 323 were influenza outbreaks, involving 85 531 patients. The reported influenza?like illness outbreaks occurred most frequently from November 2017 to January 2018 in both the southern and northern regions and the highest peaks were in December 2017. During the period 1 850 influenza?like illness outbreaks (77.15%) were reported in the southern region, and 548 influenza?like illness outbreaks (22.85%) were reported in the northern region. The most of the outbreaks occurred in primary, secondary schools and nursery care schools, with a total of 2 210 reports (92.16%). And the majority of the outbreaks involved 10-29 incident cases. The dominant isolated virus strains for the outbreaks were influenza B (1 505 outbreaks, 62.76% of all the outbreaks). Conclusion Seasonality of influenza outbreaks were observed in mainland China during 2017-2018 surveillance season and the reported influenza outbreaks were most frequently occurred in autumn?winter season and in southern China. Primary, secondary schools and nursery care schools are high?risk places for outbreaks, and the dominant isolated virus strains for the outbreaks were influenza B.

Objective To analyze epidemiological characteristics of influenza?like illness outbreaks in mainland China during 2017-2018 surveillance season, and to provide scientific evidence for developing influenza prevention and control strategies. Methods We collected the data on reported influenza outbreaks in 2017-2018 surveillance season from China Influenza Surveillance Information System and China Public Health Emergency Management Information System and analyzed the data of laboratory?confirmed influenza?like illness outbreaks by descriptive epidemiological methods. Results During the surveillance season, a total of 2 398 influenza?like illness outbreaks (with 10 or more incidences in an outbreak) in mainland China were reported, involving 87 084 patients, of which 2 323 were influenza outbreaks, involving 85 531 patients. The reported influenza?like illness outbreaks occurred most frequently from November 2017 to January 2018 in both the southern and northern regions and the highest peaks were in December 2017. During the period 1 850 influenza?like illness outbreaks (77.15%) were reported in the southern region, and 548 influenza?like illness outbreaks (22.85%) were reported in the northern region. The most of the outbreaks occurred in primary, secondary schools and nursery care schools, with a total of 2 210 reports (92.16%). And the majority of the outbreaks involved 10-29 incident cases. The dominant isolated virus strains for the outbreaks were influenza B (1 505 outbreaks, 62.76% of all the outbreaks). Conclusion Seasonality of influenza outbreaks were observed in mainland China during 2017-2018 surveillance season and the reported influenza outbreaks were most frequently occurred in autumn?winter season and in southern China. Primary, secondary schools and nursery care schools are high?risk places for outbreaks, and the dominant isolated virus strains for the outbreaks were influenza B.

Objective: To isolate the cross-reactive antibodies against hemagglutinin of influenza virus and identify its biological function. Methods: The antibodies gene reservoir of cross-reactive and H5N1 pseudotype particles neutralizing B cell circulating in peripheral blood of a human H5N1 case was recovered by in vitro B cell culture, screening, RT-PCR and expression vector cloning techniques. The Ab gene pairing was screened by transient transfection of human kidney 293T cells and detected using ELISA and neutralization test. The heterosubtypic antibodies were prepared and characterized. Results: We discovered the VH1-2-based heterosubtypic antibodies from two B cell lineages could neutralize GX-H5N1 pseudotype particles and have broader binding with Group 1 (including H1, H5, H6 and H9) and H7 subtype. Conclusions Cross-reactive antibodies can be induced by H5N1 infection.

Objective: To develop the monoclonal antibody (mAb) against neuraminidase of H7N9 subtype influenza A virus and identify its biological function. Methods: Female 8 week-old BALB/c mice were immunized and the splenocytes of the mice were fused with Sp2/0 myeloma cells. Indirect ELISA was used to screen hybridoma and the positive clones were subject to be subcloned. Positive clones were identified and the monoclonal antibodies(mAbs) were obtained by purifying the ascetic fluid of mice injected with the hybridoma. The NA-binding as well as neuraminidase-inhibition activity of these mAbs were determined. Results: Three mAbs against neuraminidase of H7N9 subtype influenza A virus, 1G8, 3C4 and 4E8, were obtained. They demonstrated different epitop-recognizing. 3C4 and 4E8 exhibited neuraminidase inhibitory activity, with a IC₅₀ of 1.45 μg/ml and 8.65 μg/ml, respectively. Conclusions The results suggested that mAbs specific to neuraminidase of H7N9 subtype influenza A virus were developed, providing an useful tool in control and preventing the novel H7N9 influenza A virus.