Analysis of influenza B virus lineages and the HA1 domain of its hemagglutinin gene in Guangzhou, southern China, during 2016

Increasing serum antibodies against type B influenza virus in 2017-2018 winter in Beijing, China

Influenza B virus circulates yearly with lower activity than that of influenza A virus in China. During winter 2017 to 2018, a sharp surge of influenza activity dominated by type B/Yamagata lineage virus caused unprecedented medical burden in Beijing. This research aimed to understand the underlying mechanism for this circulation and prepare for epidemics in the future. Sera samples collected from the patients in 2016–2017 and 2017–2018 flu seasons were tested for profiling hemagglutinin inhibition (HI) antibodies against both prevailing Victoria and Yamagata lineages of type B influenza viruses. It showed that the seroprevalence against both lineages of the virus in 2017–2018 winter was higher than that in 2016–2017, while no difference of the seroprevalence was observed between the two viruses. Meanwhile, significant elevated geometric mean titer (GMT) against both lineages of influenza B viruses was found in the specimens collected during 2017–2018 flu season than that from 2016 to 2017, suggesting the viruses might undergo antigenic changes. These results also suggested that lower GMT against both type B variants in 2016–2017 might serve as an immunological niche for the dominating of B/Yamagata virus in China during 2017–2018 winter season. Our findings have implication that there was a significantly elevation of HI antibodies to influenza viruses B in 2017–2018 than in 2016–2017. On the other hand, the low level of HI antibodies to both B/Y and B/V in 2016–2017 could contribute to the severe B/Y epidemic in 2017–2018 to some extent.

Detection and characterization of type B influenza virus from influenza-like illness cases during the 2017-2018 winter influenza season in Beijing, China

In the winter of 2017-2018, there was significant influenza activity in China, resulting in unprecedented usage of influenza rapid antigen tests (IRAT) and neuraminidase inhibitors (NAIs). The aim of this study was to characterize the most prevalent influenza virus type in a clinical setting with respect to diagnosis and concomitant NAI treatment. From Dec 2017 to Jan 2018, 3257 patients with influenza-like illness (ILI) were screened using IRAT. We summarized and compared the results with the last influenza season. Subtyping of influenza B viruses and identification of NAI drug resistance mutations were carried out by sequencing the HA and NA genes and aligning these with genetic isotypes. The performance of IRAT and RT-PCR was compared. Screening results indicated that influenza B virus was the leading cause of this influenza epidemic, with children being more susceptible to infection than adults. Phylogenetic analysis revealed that the prevailing influenza B virus belonged to the Yamagata lineage and were genetically similar to strains isolated from North America in the same influenza season. Cross-continental spread of influenza/B/Yamagata occurred. NAI resistance mutations were not identified in the 18 samples analyzed. The current antiviral protocol was still effective for influenza B control. RT-PCR positivity was significantly higher than that of IRAT (P = 0.004). IRAT and RT-PCR had a consistency rate of 86.9%, with the consistency rates of the positive and negative cases being 54.3% and 97.3%, respectively. Clinicians should be alert to the possibility of obtaining false negative results when using IRAT, and RT-PCR is recommended to improve the accuracy of pathogen detection.