Influenza vaccine effectiveness against laboratory-confirmed influenza in a vaccine-mismatched influenza B-dominant season

Epidemic patterns of the different influenza virus types and subtypes/lineages for 10 years in Chongqing, China, 2010-2019

To optimize seasonal influenza control and prevention programs in regions with potentially complicated seasonal patterns. Descriptive epidemiology was used to analyze the etiology of influenza, and chi-square tests were used to compare the epidemic patterns among different influenza virus types and subtypes/lineages. From January 2010 to December 2019, a total of 63,626 ILI cases were reported in Chongqing and 14,136 (22.22%) were laboratory-confirmed influenza cases. The proportions of specimens positive for influenza A and influenza B were 13.32% (8,478/63,626) and 8.86% (5,639/63,626), respectively. The proportion of positive specimens for influenza A reached the highest in winter (23.33%), while the proportion of positive specimens for influenza B reached the highest in spring (11.88%). Children aged 5-14 years old had the highest proportion of positive specimens for influenza. The influenza virus types/subtypes positive was significantly different by seasons and age groups (P<.001), but not by gender (p = .436). The vaccine strains were matched to the circulating influenza virus strains in all other years except for 2018 (vaccine strain was B/Colorado/06/2017; circulating strain was B/Yamagata). The study showed significant variations in epidemic patterns, including seasonal epidemic period and age distributions, among different influenza types, subtypes/lineages in Chongqing. Influenza vaccines matched to the circulating influenza virus strain in nine of the ten years. To prevent and mitigate the influenza outbreaks in this area, high risk population, especially children aged 5-14 years, are encouraged to get vaccinated against influenza before the epidemic seasons.

Proteomics analysis of methionine enkephalin upregulated macrophages against infection by the influenza-A virus

Macrophages have a vital role in phagocytosis and antiviral effect against invading influenza viruses. Previously, we found that methionine enkephalin (MENK) inhibited influenza virus infection by upregulating the "antiviral state" of macrophages. To investigate the immunoregulatory mechanism of action of MENK on macrophages, we employed proteomic analysis to identify differentially expressed proteins (DEPs) between macrophages infected with the influenza-A virus and cells infected with the influenza-A virus after pretreatment with MENK. A total of 215 DEPs were identified: 164 proteins had upregulated expression and 51 proteins had downregulated expression. Proteomics analysis showed that DEPs were highly enriched in "cytokine-cytokine receptor interaction", "phagosome", and "complement and coagulation cascades pathway". Proteomics analysis revealed that MENK could be an immune modulator or prophylactic for the prevention and treatment of influenza. MENK promoted the polarization of M1 macrophages, activated inflammatory responses, and enhanced phagocytosis and killing function by upregulating opsonizing receptors.

Antiviral Approaches against Influenza Virus

Preventing and controlling influenza virus infection remains a global public health challenge, as it causes seasonal epidemics to unexpected pandemics. These infections are responsible for high morbidity, mortality, and substantial economic impact. Vaccines are the prophylaxis mainstay in the fight against influenza. However, vaccination fails to confer complete protection due to inadequate vaccination coverages, vaccine shortages, and mismatches with circulating strains. Antivirals represent an important prophylactic and therapeutic measure to reduce influenza-associated morbidity and mortality, particularly in high-risk populations. Here, we review current FDA-approved influenza antivirals with their mechanisms of action, and different viral- and host-directed influenza antiviral approaches, including immunomodulatory interventions in clinical development. Furthermore, we also illustrate the potential utility of machine learning in developing next-generation antivirals against influenza.

Characterization of influenza B viruses with reduced susceptibility to influenza neuraminidase inhibitors

A total of 3425 influenza B viruses collected from the Asia-Pacific region were tested against the four registered neuraminidase inhibitors (NAIs) (oseltamivir carboxylate, zanamivir, peramivir and laninamivir) as part of the routine surveillance work at the WHO Collaborating Centre for Research and Reference on Influenza, Melbourne between 2016 and 2020. Forty-five influenza B viruses with reduced susceptibility to one or more NAIs were identified. While the majority of these had neuraminidase (NA) mutations that were known to confer NAIs resistance, fifteen had NA mutations that had not been confirmed as being responsible for reduced NAIs susceptibility. Eleven of these NA mutations of concern were investigated using reverse genetics (RG) techniques to verify that these mutations were the cause of the reduced NAI susceptibility. All mutations were introduced separately into the NA of B/Brisbane/27/2016 (a B Victoria-lineage virus) or B/Yamanashi/166/98 (a B Yamagata-lineage virus) and the effects of these were analysed by an in vitro NAI assay. The T146K substitution in the NA of B Victoria and Yamagata-lineages resulted in a large increase in the IC₅₀ for peramivir (>1000-fold increase in the mean IC₅₀ of sensitive viruses with T146) with smaller increases for zanamivir and oseltamivir. A proline substitution (T146P) had a slightly lower (>700-fold) effect on the peramivir IC₅₀ and also on the other NAIs. The presence of a second NA mutation at N169S combined with the T146P further increased the IC₅₀ of peramivir (>7000-fold) and the other NAIs. A synergistic effect was also confirmed for dual NA mutations with G247D + I361V which showed a modest increase in the IC₅₀ for oseltamivir (6-fold). Only one of two RG-viruses with the mutation G108E could be rescued and it had a high IC₅₀ against zanamivir (>4000-fold) and laninamivir (>7000-fold), but a lower IC₅₀ against oseltamivir (>200-fold). NA mutations H101L, A200T, D432G, H439P and H439R were also confirmed to somewhat reduce the in vitro susceptibility of influenza B viruses to the NAIs. Overall, this study identifies the potential impact of selected mutations on the clinical performance of NAIs when used to treat influenza B infection in humans.

Lineage-specific protection and immune imprinting shape the age distributions of influenza B cases

How a history of influenza virus infections contributes to protection is not fully understood, but such protection might explain the contrasting age distributions of cases of the two lineages of influenza B, B/Victoria and B/Yamagata. Fitting a statistical model to those distributions using surveillance data from New Zealand, we found they could be explained by historical changes in lineage frequencies combined with cross-protection between strains of the same lineage. We found additional protection against B/Yamagata in people for whom it was their first influenza B infection, similar to the immune imprinting observed in influenza A. While the data were not informative about B/Victoria imprinting, B/Yamagata imprinting could explain the fewer B/Yamagata than B/Victoria cases in cohorts born in the 1990s and the bimodal age distribution of B/Yamagata cases. Longitudinal studies can test if these forms of protection inferred from historical data extend to more recent strains and other populations.