Re-emergence of H3N2 strains carrying potential neutralizing mutations at the N-linked glycosylation site at the hemagglutinin head, post the 2009 H1N1 pandemic

Broadly Protective Neuraminidase-Based Influenza Vaccines and Monoclonal Antibodies: Target Epitopes and Mechanisms of Action

Neuraminidase (NA) is an important surface protein on influenza virions, playing an essential role in the viral life cycle and being a key target of the immune system. Despite the importance of NA-based immunity, current vaccines are focused on the hemagglutinin (HA) protein as the target for protective antibodies, and the amount of NA is not standardized in virion-based vaccines. Antibodies targeting NA are predominantly protective, reducing infection severity and viral shedding. Recently, NA-specific monoclonal antibodies have been characterized, and their target epitopes have been identified. This review summarizes the characteristics of NA, NA-specific antibodies, the mechanism of NA inhibition, and the recent efforts towards developing NA-based and NA-incorporating influenza vaccines.

Retrospective immunogenicity analysis of seasonal flu H3N2 vaccines recommended in the past ten years using immunized animal sera

BACKGROUND

Influenza A (H3N2) virus (A/H3N2) has complex antigenic evolution, resulting in frequent vaccine strain updates. We aimed to evaluate the protective effect of the vaccine strains on the circulating strains from past ten years and provide a basis for finding a broader and more efficient A/H3N2 vaccine strain.

METHODS

Eighty-four representative circulating A/H3N2 strains were selected from 65,791 deposited sequences in 2011-2020 and pseudotyped viruses were constructed with the VSV vector. We immunized guinea pigs with DNA vaccine containing the A/H3N2 components of the vaccine strains from 2011 to 2021 and tested neutralizing antibody against the pseudotyped viruses. We used a hierarchical clustering method to classify the eighty-four representative strains into different antigenic clusters. We also immunized animals with monovalent vaccine stock of the vaccine strains for the 2020-2021 and 2021-2022 seasons and tested neutralizing antibody against the pseudotyped viruses.

FINDINGS

The vaccine strains PE/09, VI/11 and TE/12 induced higher levels of neutralizing antibody against representative strains circulating in recommended year and the year immediately prior whereas vaccine strains HK/14, HK/19 and CA/20 induced poor neutralization against all representative strains. The representative strains were divided into five antigenic clusters (AgV), which were not identical to gene clades. The AgV5 strains were most difficult to be protected among the five clusters. Compared with single-dose immunization, three doses of monovalent vaccine stock (HK/19 or CA/20) could induce stronger and broader neutralizing antibodies against strains in each of the antigenic clusters.

INTERPRETATION

The protective effect of vaccine strains indicated that the accurate selection of A/H3N2 vaccine strains must remain a top priority. By increasing the frequency of immunization, stronger and broader neutralizing antibodies against strains in all antigenic clusters were induced, which provides direction for a new immunization strategy.

FUNDING

This work was supported by a grant from National Key R&D Program of China (No. 2021YFC2301700).

A changing trend in diagnostic methods of Influenza A (H3N2) virus in human: a review

The influenza virus is classified into four types A, B, C, and D, but type A and B are responsible for major illnesses in people with influenza A being the only virus responsible for flu pandemics due to the presence of two surface proteins called hemagglutinin (H) and neuraminidase (N) on the virus. The two subtypes of influenza A virus, H1N1 and H3N2, have been known to cause many flu pandemics. Both subtypes change genetically and antigenically to produce variants (clades and subclades, also know as groups and subgroups). H3N2 tends to change rapidly, both genetically and antigenically whereas that of H1N1 generally tends to have smaller changes. Influenza A (H3N2) viruses have evolved to form many separate, genetically different clades that continue to co-circulate. Influenza A(H3N2) viruses have caused significant deaths as per WHO report. The review describes methods for detection of influenza A(H3N2) viruses by conventional serological methods as well as the advanced methods of molecular biology and biosensors. All these methods are based on different parameters and have different targets but the goal is to improve specificity and increase sensitivity. Amongst the molecular methods, real-time polymerase chain reaction (RT-PCR) is considered a gold standard test due to its many advantages whereas a number of other molecular methods are time-consuming, complex to perform or lack specificity. The review also considers bio-sensing methods for simple, rapid, highly sensitive, and specific detection of H3N2. The classification and principle of various H3N2 biosensors are also discussed.

Antigenic drift of hemagglutinin and neuraminidase in seasonal H1N1 influenza viruses from Saudi Arabia in 2014 to 2015

Antigenic drift of the hemagglutinin (HA) and neuraminidase (NA) proteins of the influenza virus cause a decrease in vaccine efficacy. Since the information about the evolution of these viruses in Saudi is deficient so we investigated the genetic diversity of circulating H1N1 viruses. Nasopharyngeal aspirates/swabs collected from 149 patients hospitalized with flu-like symptoms during 2014 and 2015 were analyzed. Viral RNA extraction was followed by a reverse transcription-polymerase chain reaction and genetic sequencing. We analyzed complete gene sequences of HA and NA from 80 positive isolates. Phylogenetic analysis of HA and NA genes of 80 isolates showed similar topologies and co-circulation of clades 6b. Genetic diversity was observed among circulating viruses belonging to clade 6B.1A. The amino acid residues in the HA epitope domain were under purifying selection. Amino acid changes at key antigenic sites, such as position S101N, S179N (antigenic site-Sa), I233T (antigenic site-Sb) in the head domain might have resulted in antigenic drift and emergence of variant viruses. For NA protein, 36% isolates showed the presence of amino acid changes such as V13I (n = 29), I314M (n = 29) and 12% had I34V (n = 10). However, H257Y mutation responsible for resistance to neuraminidase inhibitors was missing. The presence of amino acid changes at key antigenic sites and their topologies with structural mapping of residues under purifying selection highlights the importance of antigenic drift and warrants further characterization of recently circulating viruses in view of vaccine effectiveness. The co-circulation of several clades and the predominance of clade 6B.1 suggest multiple introductions in Saudi.

Conserved HA-peptides expressed along with flagellin in Trichoplusia ni larvae protects chicken against intranasal H7N1 HPAIV challenge

The immunization of poultry where H5 and H7 influenza viruses (IVs) are endemic is one of the strategies to prevent unexpected zoonoses. Our group has been focused on conserved HA-epitopes as potential vaccine candidates to obtain multivalent immune responses against distinct IV subtypes. In this study, two conserved epitopes (NG-34 and CS-17) fused to flagellin were produced in a Baculovirus platform based on Trichoplusia ni larvae as living biofactories. Soluble extracts obtained from larvae expressing "flagellin-NG34/CS17 antigen" were used to immunize chickens and the efficacy of the vaccine was evaluated against a heterologous H7N1 HPAIV challenge in chickens. The flagellin-NG34/CS17 vaccine protected the vaccinated chickens and blocked viral shedding orally and cloacally. Furthermore, no apparent clinical signs were monitored in 10/12 vaccinated individuals. The mechanism of protection conferred is under investigation.

H3N2 influenza viruses in humans: Viral mechanisms, evolution, and evaluation

Annual seasonal influenza vaccines are composed of two influenza A strains representing the H1N1 and H3N2 subtypes, and two influenza B strains representing the Victoria and Yamagata lineages. Strains from these Influenza A and Influenza B viruses currently co-circulate in humans. Of these, strains associated with the H3N2 subtype are affiliated with severe influenza seasons. H3N2 influenza viruses pre-dominated during 3 of the last 5 quite severe influenza seasons. During the 2016/2017 flu season, the H3N2 component of the influenza vaccine exhibited a poor protective efficacy (∼28-42%) against preventing infection of co-circulating strains. Since their introduction to the human population in 1968, H3N2 Influenza viruses have rapidly evolved both genetically and antigenically in an attempt to escape host immune pressures. As a result, these viruses have added numerous N-linked glycans to the viral hemagglutinin (HA), increased the overall net charge of the HA molecule, changed their preferences in receptor binding, and altered the ability of neuraminidase (NA) to agglutinate red blood cells prior to host entry. Over time, these adaptations have made characterizing these viruses increasingly difficult. This review investigates these recent changes in modern H3N2 influenza viruses and explores the methods that researchers are currently developing in order to study these viruses.

Inactivated H7 Influenza Virus Vaccines Protect Mice despite Inducing Only Low Levels of Neutralizing Antibodies

Avian influenza viruses of the H7 hemagglutinin (HA) subtype present a significant public health threat, as evidenced by the ongoing outbreak of human A(H7N9) infections in China. When evaluated by hemagglutination inhibition (HI) and microneutralization (MN) assays, H7 viruses and vaccines are found to induce lower level of neutralizing antibodies (nAb) than do their seasonal counterparts, making it difficult to develop and evaluate prepandemic vaccines. We have previously shown that purified recombinant H7 HA appear to be poorly immunogenic in that they induce low levels of HI and MN antibodies. In this study, we immunized mice with whole inactivated reverse genetics reassortant (RG) viruses expressing HA and neuraminidase (NA) from 3 different H7 viruses [A/Shanghai/2/2013(H7N9), A/Netherlands/219/2003(H7N7), and A/New York/107/2003(H7N2)] or with human A(H1N1)pdm09 (A/California/07/2009-like) or A(H3N2) (A/Perth16/2009) viruses. Mice produced equivalent titers of antibodies to all viruses as measured by enzyme-linked immunosorbent assay (ELISA). However, the antibody titers induced by H7 viruses were significantly lower when measured by HI and MN assays. Despite inducing very low levels of nAb, H7 vaccines conferred complete protection against homologous virus challenge in mice, and the serum antibodies directed against the HA head region were capable of mediating protection. The apparently low immunogenicity associated with H7 viruses and vaccines may be at least partly related to measuring antibody titers with the traditional HI and MN assays, which may not provide a true measure of protective immunity associated with H7 immunization. This study underscores the need for development of additional correlates of protection for prepandemic vaccines.IMPORTANCE H7 avian influenza viruses present a serious risk to human health. Preparedness efforts include development of prepandemic vaccines. For seasonal influenza viruses, protection is correlated with antibody titers measured by hemagglutination inhibition (HI) and virus microneutralization (MN) assays. Since H7 vaccines typically induce low titers in HI and MN assays, they have been considered to be poorly immunogenic. We show that in mice H7 whole inactivated virus vaccines (WIVs) were as immunogenic as seasonal WIVs, as they induced similar levels of overall serum antibodies. However, a larger fraction of the antibodies induced by H7 WIV was nonneutralizing in vitro Nevertheless, the H7 WIV completely protected mice against homologous viral challenge, and antibodies directed against the HA head were the major contributor toward immune protection. Vaccines against H7 avian influenza viruses may be more effective than HI and virus neutralization assays suggest, and such vaccines may need other methods for evaluation.

Usefulness of multiplex PCR methods and respiratory viruses' distribution in children below 15 years old according to age, seasons and clinical units in France: A 3 years retrospective study

Background

To date, only influenza and RSV testing are recommended for respiratory viruses’ detection in paediatric units. In this study, we described, according to seasons, ages and clinical units, the results obtained in children (<15 years old) by multiplex-PCR (mPCR) tests allowing a quick and wide range detection of all respiratory viruses. These results were also compared with RSV specific detection.

Methods

All nasopharyngeal mPCR and RSV tests requested by clinicians in our French teaching hospitals group between 2011 and 2014 were retrospectively included. All repeated samples for the same children in the same month were discarded.

Results

Of the 381 mPCR tests (344 children) performed, 51.4% were positive. Positivity and viral co-infection rates were higher in the 6–36 months old strata (81% and 25%, p<0.0001 and p = 0.04, respectively). Viral distribution showed strong variations across ages. During specific influenza epidemic periods, only 1/39 (2.5%) mPCR tests were positive for influenza and 19/39 (48.7%) for other viruses. During specific RSV epidemic periods, only 8/46 (17.4%) mPCR tests were positive for RSV and 14/46 (30.4%) for other viruses. 477/1529 (31.2%) of RSV immunochromatography-tests were positive. Among the negatives immunochromatography-test also explored by mPCR, 28/62 (31%) were positive for other respiratory viruses.

Conclusion

This study provides a wide description of respiratory viruses’ distribution among children in hospital settings using mPCR over 3 years. It emphasizes the number of undiagnosed respiratory viruses according to the current diagnosis practice in France and gives a better picture of respiratory viruses identified in hospital settings by mPCR all over the year in France.