Antigenic variants of influenza B viruses isolated in Japan during the 2017-2018 and 2018-2019 influenza seasons

Existing Evidence for Influenza B Virus Adaptations to Drive Replication in Humans as the Primary Host

Influenza B virus (IBV) is one of the two major types of influenza viruses that circulate each year. Unlike influenza A viruses, IBV does not harbor pandemic potential due to its lack of historical circulation in non-human hosts. Many studies and reviews have highlighted important factors for host determination of influenza A viruses. However, much less is known about the factors driving IBV replication in humans. We hypothesize that similar factors influence the host restriction of IBV. Here, we compile and review the current understanding of host factors crucial for the various stages of the IBV viral replication cycle. While we discovered the research in this area of IBV is limited, we review known host factors that may indicate possible host restriction of IBV to humans. These factors include the IBV hemagglutinin (HA) protein, host nuclear factors, and viral immune evasion proteins. Our review frames the current understanding of IBV adaptations to replication in humans. However, this review is limited by the amount of research previously completed on IBV host determinants and would benefit from additional future research in this area.

Molecular characterization and evolution dynamics of influenza B viruses circulating in Germany from season 1996/1997 to 2019/2020

Influenza B viruses are responsible for significant disease burden caused by viruses of both the Yamagata- and Victoria-lineage. Since the circulating patterns of influenza B viruses in different countries vary we investigated molecular properties and evolution dynamics of influenza B viruses circulating in Germany between 1996 and 2020. A change of the dominant lineage occurred in Germany in seven seasons in over past 25 years. A total of 676 sequences of hemagglutinin coding domain 1 (HA1) and 516 sequences of neuraminidase (NA) genes of Yamagata- and Victoria-lineage viruses were analyzed using time-scaled phylogenetic tree. Phylogenetic analysis demonstrated that Yamagata-lineage viruses are more diverse than the Victoria-lineage viruses and could be divided into nine genetic groups whereas Victoria-lineage viruses presented six genetic groups. Comparative phylogenetic analyses of both the HA and NA segments together revealed a number of inter-lineage as well as inter- and intra-clade reassortants. We identified key amino acid substitutions in major HA epitopes such as in four antigenic sites and receptor-binding sites (RBS) and in the regions close to them, with most substitutions in the 120-loop of both lineage viruses. Altogether, seventeen substitutions were fixed over time within the Yamagata-lineage with twelve of them in the antigenic sites. Thirteen substitutions were identified within the Victoria-lineage, with eleven of them in the antigenic sites. Moreover, all Victoria-lineage viruses of the 2017/2018 season were characterized by a deletion of two amino acids at the position 162-163 in the antigenic site of HA1. The viruses with triple deletion Δ162-164 were found in Germany since season 2018/2019. We highlighted the interplay between substitutions in the glycosylation sites and RBS and antigenic epitope during HA evolution. The results obtained underscore the need for continuous monitoring of circulating influenza B viruses. Early detection of strains with genetic and antigenic variation is essential to predict the circulation patterns for the following season. Such information is important for the development of optimal vaccines and strategies for prevention and control of influenza.

Incidence and neutralizing antibody seroprevalence of influenza B virus in Egypt: Results of a community-based cohort study

Since 2000, two lineages of influenza B viruses, Victoria and Yamagata, have been circulating at similar frequencies worldwide. Little is known about the circulation of those viruses in Egypt. This study aims to describe the epidemiology of influenza B virus infections in Egypt, 2017–2019. This was performed through a household prospective cohort study on influenza infections among 2400 individuals from five villages. When a study participant had influenza like symptoms, a nasal swab and an oropharyngeal swab were obtained and tested by RT-PCR for influenza B infections. A serum sample was obtained from all participants annually to detect neutralizing antibodies using microneutralization assay. 9.1% of subjects were positive for influenza B viruses during season 2017–2018 mostly among preschoolers and 7.6% were positive during the season 2018–2019 with higher risk in females, potentially due to mothers being infected after contact with their children. The overall seroprevalence among the participants was 53.2% and 52.2% against the Victoria and Yamagata lineages respectively, the majority of seropositive participants were students. Multivariate analysis showed that age and having chronic diseases were the strongest predictors of infection. Our results show that both influenza B lineages circulated between 2017 and 2020 in Egypt almost in equal proportion. Encouraging the uptake of seasonal influenza vaccines is recommended.

Expanding Mouse-Adapted Yamagata-like Influenza B Viruses in Eggs Enhances In Vivo Lethality in BALB/c Mice

Despite the yearly global impact of influenza B viruses (IBVs), limited host range has been a hurdle to developing a readily accessible small animal disease model for vaccine studies. Mouse-adapting IBV can produce highly pathogenic viruses through serial lung passaging in mice. Previous studies have highlighted amino acid changes throughout the viral genome correlating with increased pathogenicity, but no consensus mutations have been determined. We aimed to show that growth system can play a role in mouse-adapted IBV lethality. Two Yamagata-lineage IBVs were serially passaged 10 times in mouse lungs before expansion in embryonated eggs or Madin-Darby canine kidney cells (London line) for use in challenge studies. We observed that virus grown in embryonated eggs was significantly more lethal in mice than the same virus grown in cell culture. Ten additional serial lung passages of one strain again showed virus grown in eggs was more lethal than virus grown in cells. Additionally, no mutations in the surface glycoprotein amino acid sequences correlated to differences in lethality. Our results suggest growth system can influence lethality of mouse-adapted IBVs after serial lung passaging. Further research can highlight improved mechanisms for developing animal disease models for IBV vaccine research.

Epidemiology of influenza virus reinfection in Guangxi, China: a retrospective analysis of a nine-year influenza surveillance data

BACKGROUND

Epidemiological characteristics profile of the reinfection of the influenza virus has not been well described.

METHODS

Included all influenza cases of Guangxi, China from January 2011 to December 2019 recorded in National Notifiable Infectious Disease Reporting Information System (NIDRIS) within 24 hours after diagnosis.

RESULTS

A total of 53,605.6 person-months and the median time of 8.7 months were observed for reinfection. The median age at the first influenza virus infection was 4.5 (IQR=2.0-7.5) years. The cumulative reinfection incidence was 2% at 6-month, 4% at 12-month, 5% at 24-month, and 7% after 59-month. Living in the rural area (HR=1.37 [95%CI, 1.29-1.45]), age ≤6 years (HR=11.43 [95%CI, 9.47-13.80]) were independent risk factors associated with influenza reinfection. Among 49 patients experiencing twice laboratory tests, 32 patients (65.3%) were with different virus types. The interval between two consecutive laboratory-confirmed episodes of the four groups differed (p=0.148), as the maximum was 72.9 months, and the minimum was 1.2 months.

CONCLUSIONS

The reinfection of the influenza virus in Guangxi independently and positively associated with the rural area and younger age. The unusually high frequency of reinfection points to a need for further prospective longitudinal studies to better investigate sufficient impact on different subtypes.

Antigenic variants of influenza B viruses isolated in Japan during the 2017-2018 and 2018-2019 influenza seasons

Background

Here, we genetically and antigenically analyzed influenza B viruses (IBVs) isolated in Japan during the 2017‐2018 and 2018‐2019 influenza seasons.

Methods

A total of 68 IBVs (61 B/Yamagata/16/88‐like [B/Yamagata]‐lineage and 7 B/Victoria/2/87‐like [B/Victoria]‐lineage) were antigenically and genetically characterized by using hemagglutination inhibition (HI) assays and phylogenetic analysis, respectively. The susceptibility of IBVs to neuraminidase (NA) inhibitors was assessed by using a fluorescence‐based NA inhibition assay.

Results

All 61 B/Yamagata‐lineage isolates were genetically closely related to B/Phuket/3073/2013, the vaccine strain for these two seasons. Eleven B/Yamagata‐lineage isolates tested were antigenically similar to B/Phuket/3073/2013 by the HI test. Seven B/Victoria‐lineage isolates were genetically closely related to B/Texas/02/2013, the WHO‐recommended vaccine strain for the 2017‐2018 season; however, they were antigenically distinct from B/Texas/02/2013 with an eightfold or 16‐fold difference in HI titer. Of these 7 isolates, 4 possessed a two‐amino‐acid deletion at positions 162 and 163 in hemagglutinin (HA) and the other 3 had a three‐amino‐acid deletion at positions 162‐164 in HA. Importantly, the variants with the three‐amino‐acid deletion appeared to be antigenically different from the B/Colorado/06/2017 virus with the two‐amino‐acid deletion, the vaccine strain for the 2018‐2019 season with a fourfold or eightfold difference in HI titer. One B/Yamagata‐lineage isolate carrying a G407S mutation in its NA showed a marked reduction in susceptibility to zanamivir, peramivir, and laninamivir.

Conclusions

These results highlight the need for continued monitoring for the prevalence of the antigenic variant with the three‐amino‐acid deletion and the variant with reduced NA inhibitor susceptibility.