Passive immunotherapies for the next influenza pandemic

Influenzavirus is among the most relevant candidates for a next pandemic. We review here the phylogeny of former influenza pandemics, and discuss candidate lineages. After briefly reviewing the other existing antiviral options, we discuss in detail the evidences supporting the efficacy of passive immunotherapies against influenzavirus, with a focus on convalescent plasma.

Clinical, epidemiological, and genomic characteristics of a seasonal influenza A virus outbreak in Beijing: A descriptive study

China experienced a severe influenza season that began at the end of February 2023. The aim of this post hoc analysis was to investigate the clinical, epidemiological, and genomic features of this outbreak in Beijing. The number of cases increased rapidly from the end of February and reached its peak in March, with 7262 confirmed cases included in this study. The median age was 33 years, and 50.3% of them were male. The average daily positive rate reached 69% during the peak period. The instantaneous reproduction number (Rt) showed a median of 2.1, exceeded 2.5 initially, and remaining above 1 for the following month. The most common symptoms were fever (75.0%), cough (51.0%), and expectoration (42.9%), with a median body temperature of 38.5°C (interquartile range 38-39). Eight clinical symptoms were more likely to be observed in cases with fever, with odds ratio greater than 1. Viral shedding time ranged from 3 to 25 days, with median of 7.5 days. The circulating viruses in Beijing mainly included H1N1pdm09 (clades 5a.2a and 5a.2a.1), following with H3N2 (clade 2a.2a.3a.1). The descriptive study suggests that influenza viruses in this influenza season had a higher transmissibility and longer shedding duration, with fever being the most common symptom.

Characterization of Influenza A(H1N1)pdm09 Viruses Isolated in the 2018-2019 and 2019-2020 Influenza Seasons in Japan

The influenza A(H1N1)pdm09 virus that emerged in 2009 causes seasonal epidemic worldwide. The virus acquired several amino acid substitutions that were responsible for antigenic drift until the 2018-2019 influenza season. Viruses possessing mutations in the NA and PA proteins that cause reduced susceptibility to NA inhibitors and baloxavir marboxil, respectively, have been detected after antiviral treatment, albeit infrequently. Here, we analyzed HA, NA, and PA sequences derived from A(H1N1)pdm09 viruses that were isolated during the 2018-2019 and 2019-2020 influenza seasons in Japan. We found that A(H1N1)pdm09 viruses possessing the D187A and Q189E substitutions in HA emerged and dominated during the 2019-2020 season; these substitutions in the antigenic site Sb, a high potency neutralizing antibody-eliciting site for humans, changed the antigenicity of A(H1N1)pdm09 viruses. Furthermore, we found that isolates possessing the N156K substitution, which was predicted to affect the antigenicity of A(H1N1)pdm09 virus at the laboratory level, were detected at a frequency of 1.0% in the 2018-2019 season but 10.1% in the 2019-2020 season. These findings indicate that two kinds of antigenically drifted viruses-N156K and D187A/Q189E viruses-co-circulated during the 2019-2020 influenza season in Japan.

Whole-genome analysis to determine the rate and patterns of intra-subtype reassortment among influenza type-A viruses in Africa

Influenza type-A viruses (IAVs) present a global burden of human respiratory infections and mortality. Genome reassortment is an important mechanism through which epidemiologically novel influenza viruses emerge and a core step in the safe reassortment-incompetent live-attenuated influenza vaccine development. Currently, there are no data on the rate, spatial and temporal distribution, and role of reassortment in the evolution and diversification of IAVs circulating in Africa. We aimed to detect intra-subtype reassortment among Africa pandemic H1N1pdm09 (2009-10), seasonal H1N1pdm09 (2011-20), and seasonal H3N2 viruses and characterize the genomic architecture and temporal and spatial distribution patterns of the resulting reassortants. Our study was nested within the Uganda National Influenza Surveillance Programme. Next-generation sequencing was used to generate whole genomes (WGs) from 234 H1N1pdm09 (n = 116) and H3N2 (n = 118) viruses sampled between 2010 and 2018 from seven districts in Uganda. We combined our newly generated WGs with 658 H1N1pdm09 and 1131 H3N2 WGs sampled between 1994 and 2020 across Africa and identified reassortants using an automated Graph Incompatibility Based Reassortment Finder software. Viral reassortment rates were estimated using a coalescent reassortant constant population model. Phylogenetic analysis was used to assess the effect of reassortment on viral genetic evolution. We observed a high frequency of intra-subtype reassortment events, 12 · 4 per cent (94/758) and 20 · 9 per cent (256/1,224), and reassortants, 13 · 3 per cent (101/758) and 38 · 6 per cent (472/1,224), among Africa H1N1pdm09 and H3N2 viruses, respectively. H1N1pdm09 reassorted at higher rates (0.1237-0.4255) than H3N2 viruses (0 · 00912-0.0355 events/lineage/year), a case unique to Uganda. Viral reassortants were sampled in 2009 through 2020, except in 2012. 78 · 2 per cent (79/101) of H1N1pdm09 reassortants acquired new non-structural, while 57 · 8 per cent (273/472) of the H3N2 reassortants had new hemagglutinin (H3) genes. Africa H3N2 viruses underwent more reassortment events involving larger reassortant sets than H1N1pdm09 viruses. Viruses with a specific reassortment architecture circulated for up to five consecutive years in specific countries and regions. The Eastern (Uganda and Kenya) and Western Africa harboured 84 · 2 per cent (85/101) and 55 · 9 per cent (264/472) of the continent's H1N1pdm09 and H3N2 reassortants, respectively. The frequent reassortment involving multi-genes observed among Africa IAVs showed the intracontinental viral evolution and diversification possibly sustained by viral importation from outside Africa and/or local viral genomic mixing and transmission. Novel reassortant viruses emerged every year, and some persisted in different countries and regions, thereby presenting a risk of influenza outbreaks in Africa. Our findings highlight Africa as part of the global influenza ecology and the advantage of implementing routine whole-over partial genome sequencing and analyses to monitor circulating and detect emerging viruses. Furthermore, this study provides evidence and heightens our knowledge on IAV evolution, which is integral in directing vaccine strain selection and the update of master donor viruses used in recombinant vaccine development.

Functional and Binding H1N1pdm09-Specific Antibody Responses in Occasionally and Repeatedly Vaccinated Healthcare Workers: A Five-Year Study (2009-2014)

Background

In 2009, a novel influenza A/H1N1pdm09 emerged and caused a pandemic. This strain continued to circulate and was therefore included in the seasonal vaccines up to the 2016/2017-season. This provided a unique opportunity to study the long-term antibody responses to H1N1pdm09 in healthcare workers (HCW) with a different vaccination history.

Methods

HCW at Haukeland University Hospital, Bergen, Norway were immunized with the AS03-adjuvanted H1N1pdm09 vaccine in 2009 (N=55) and divided into groups according to their vaccination history; one vaccination (N=10), two vaccinations (N=15), three vaccinations (N=5), four vaccinations (N=15) and five vaccinations (N=10). HCW are recommended for influenza vaccination to protect both themselves and their patients, but it is voluntary in Norway. Blood samples were collected pre- and at 21 days, 3, 6, and 12 months after each vaccination, or annually from 2010 HCW without vaccination. ELISA, haemagglutination inhibition (HI) and microneutralization (MN) assays were used to determine the antibody response.

Results

Pandemic vaccination induced a significant increase in the H1N1-specific antibodies measured by ELISA, HI and MN. Seasonal vaccination boosted the antibody response, both in HCW with only the current vaccination and those with prior and current vaccination during 2010/11-2013/14. We observed a trend of increased antibody responses in HCW with only the current vaccination in 2013/14. A two- and three-year gap before vaccination in 2013/14 provided a more potent antibody response compared to annually vaccinated HCW.

Conclusions

Our long term follow up study elucidates the antibody response in HCW with different vaccination histories. Our findings contribute to our understanding of the impact of repeated vaccination upon antibody responses.

Magnitude and Kinetics of T Cell and Antibody Responses During H1N1pdm09 Infection in Inbred Babraham Pigs and Outbred Pigs

We have used the pig, a large natural host animal for influenza with many physiological similarities to humans, to characterize αβ, γδ T cell and antibody (Ab) immune responses to the 2009 pandemic H1N1 virus infection. We evaluated the kinetic of virus infection and associated response in inbred Babraham pigs with identical MHC (Swine Leucocyte Antigen) and compared them to commercial outbred animals. High level of nasal virus shedding continued up to days 4 to 5 post infection followed by a steep decline and clearance of virus by day 9. Adaptive T cell and Ab responses were detectable from days 5 to 6 post infection reaching a peak at 9 to 14 days. γδ T cells produced cytokines ex vivo at day 2 post infection, while virus reactive IFNγ producing γδ T cells were detected from day 7 post infection. Analysis of NP tetramer specific and virus specific CD8 and CD4 T cells in blood, lung, lung draining lymph nodes, and broncho-alveolar lavage (BAL) showed clear differences in cytokine production between these tissues. BAL contained the most highly activated CD8, CD4, and γδ T cells producing large amounts of cytokines, which likely contribute to elimination of virus. The weak response in blood did not reflect the powerful local lung immune responses. The immune response in the Babraham pig following H1N1pdm09 influenza infection was comparable to that of outbred animals. The ability to utilize these two swine models together will provide unparalleled power to analyze immune responses to influenza.

Pathogenicity and transmissibility assessment of two strains of human influenza virus isolated in China in 2018

OBJECTIVE

Influenza season occurs every year in China, but its presentation was unusual in the period from December 2017 to early 2018. During this period, influenza activity was increasing across the country and was much greater than during the same period in previous years, with great harm to people's health.

METHODS

In this study, we isolated two human influenza virus strains-A/Hebei/F076/2018(H1N1) and B/Hebei/16275B/2018-from patients with severe influenza in Hebei, China, during the flu season in January 2018, and explored their genetic characteristics, pathogenicity, and transmissibility.

RESULTS

A/Hebei/F076/2018(H1N1) belongs to the human-like H1N1 influenza virus lineage, whereas B/Hebei/16275B/2018 belongs to the Victoria lineage and is closely related to the World Health Organization reference strain B/Brisbane/60/2008. Pathogenicity tests revealed that A/Hebei/F076/2018(H1N1) replicated much more strongly in mice, with mice exhibiting 40% mortality, whereas B/Hebei/16275B/2018 was not lethal. Both viruses could be transmitted through direct contact and by the aerosol route between guinea pigs, but the H1N1 strain exhibited higher airborne transmissibility.

CONCLUSIONS

These results may contribute to the monitoring of influenza mutation and the prevention of an influenza outbreak.

Protective efficacy of a polyvalent influenza A DNA vaccine against both homologous (H1N1pdm09) and heterologous (H5N1) challenge in the ferret model

This study describes the protective efficacy of a novel influenza plasmid DNA vaccine in the ferret challenge model. The rationally designed polyvalent influenza DNA vaccine encodes haemagglutinin and neuraminidase proteins derived from less glycosylated pandemic H1N1 (2009) and H3N2 (1968) virus strains as well as the nucleoprotein (NP) and matrix proteins (M1 and M2) from a different pandemic H1N1 (1918) strain. Needle-free intradermal immunisation with the influenza DNA vaccine protected ferrets against homologous challenge with an H1N1pdm09 virus strain, demonstrated by restriction of viral replication to the upper respiratory tract and reduced duration of viral shedding post-challenge. Breadth of protection was demonstrated in two heterologous efficacy experiments in which animals immunised with the influenza DNA vaccine were protected against challenge with a highly pathogenic avian influenza H5N1 virus strain with reproducible survival and clinical outcomes.

Bidirectional Human-Swine Transmission of Seasonal Influenza A(H1N1)pdm09 Virus in Pig Herd, France, 2018

In 2018, a veterinarian became sick shortly after swabbing sows exhibiting respiratory syndrome on a farm in France. Epidemiologic data and genetic analyses revealed consecutive human-to-swine and swine-to-human influenza A(H1N1)pdm09 virus transmission, which occurred despite some biosecurity measures. Providing pig industry workers the annual influenza vaccine might reduce transmission risk.

Galectin-1 Ameliorates Influenza A H1N1pdm09 Virus-Induced Acute Lung Injury

Influenza remains one of the major epidemic diseases worldwide. Acute lung injury mainly caused by excessive pro-inflammatory host immune responses leads to high mortality rates in severe influenza patients. Galectin-1, an animal lectin ubiquitously expressed in mammalian tissues, is reported to play important roles in viral diseases. Here, we established murine and A549 cell models to explore the potential roles of galectin-1 treatment in H1N1pdm09-induced acute lung injury. We found that galectin-1 protein level was elevated in A549 cell culture supernatants and mouse BALF after H1N1pdm09 challenge. In vivo experiments showed recombinant galectin-1 treatment reduced wet/dry weight ratio, inflammatory cell infiltration in mouse lungs and mediated the expression of cytokines and chemokines including IL-1β, IL-6, IL-10, IL-12(p40), IL-12(p70), G-CSF, MCP-1, MIP-1α and RANTES in serum and BALF of infected mice. Reduced apoptosis and viral titers in mouse lungs were also found after galectin-1 treatment. As expected, galectin-1 treated mice performed reduced body weight loss and enhanced survival rate against H1N1pdm09 challenge. In addition, in vitro experiments showed that viral titers decreased in a dose-dependent manner and cell apoptosis in A549 cells reduced after recombinant galectin-1 treatment. Taken together, our findings indicate a potentially positive effect of Gal-1 treatment on ameliorating the progress of H1N1pdm09-induced acute lung injury and recombinant galectin-1 might serve as a new agent in treating influenza.

Characterization and mutational analysis of haemagglutinin and neuraminidase of H3N2 and H1N1pdm09 human influenza A viruses in Egypt

Seasonal influenza viruses constitute a major global concern. Currently, H3N2 and H1N1pdm09 are the commonly circulating influenza A viruses. The haemagglutin and neuraminidase genes of influenza A(H3N2) and A(H1N1)pdm09 viruses from Egyptian paediatric patients with respiratory distress were sequenced. Mutational analysis of all published sequences from Egypt was evolutionary tracked for both HA and NA genes. Phylogenetic analysis of H3N2 HA showed that the Egyptian strains belong to 3C2 subclade while Egyptian A(H1N1)pdm09 strains belong to 6B1 subclade. Some Egyptian A(H1N1)pdm09, 2013–2014, strains form a new subclade; 6B3. High score of mutations were recorded in HA of H1N1pdm09 but higher was recorded in H3N2 strains. These findings confirmed a high mutation rate of influenza A subtypes specially H3N2 strains.

Efficacy of anti-influenza immunoglobulin (FLU-IGIV) in ferrets and mice infected with 2009 pandemic influenza virus

Seasonal influenza causes significant morbidity and mortality around the world each year, even with the use of vaccines and antivirals. There is a need for more effective treatments for severe and hospitalized cases of influenza. In this study, we have tested the efficacy of a human plasma-derived IgG product (FLU-IGIV) against seasonal influenza in mouse and ferret models of influenza infection. FLU-IGIV successfully protected mice (100% survival) against lethal influenza infection. Also, the survival rate observed with FLU-IGIV treatment was better than the survival rate observed with oseltamivir (60% survival). FLU-IGIV significantly reduced the viral load in the lungs compared to placebo (PBS) in ferrets infected with influenza A/California/07/2009 (H1N1pdm09) virus. Overall, these studies demonstrate the efficacy of human plasma-derived FLU-IGIV in relevant animal models of influenza virus infection.

Detection of anti-NS1 antibodies after pandemic influenza exposure: Evaluation of a serological method for distinguishing H1N1pdm09 infected from vaccinated cases

Background

Reliable exposure information is crucial for assessing health outcomes of influenza infection and vaccination. Current serological methods are unable to distinguish between anti‐hemagglutinin (HA) antibodies induced by infection or vaccination.

Objectives

We aimed to explore an alternative method for differentiating influenza infection and vaccination.

Methods

Sera from animals inoculated with influenza viruses or purified H1N1pdm09 HA were obtained. Human samples were selected from a pregnancy cohort established during the 2009 H1N1 pandemic. Unvaccinated, laboratory‐confirmed cases (N = 18), vaccinated cases without influenza‐like‐illness (N = 18) and uninfected, unvaccinated controls (N = 18) were identified based on exposure data from questionnaires, national registries and maternal hemagglutination inhibition (HI) titres at delivery. Animal and human samples were tested for antibodies against the non‐structural protein 1 (NS1) and HA from H1N1pdm09, using a Luciferase Immunoprecipitation System (LIPS).

Results

Anti‐NS1 H1N1pdm09 antibodies were detected in sera from experimentally infected, but not from vaccinated, animals. Anti‐HA H1N1pdm09 antibodies were detectable after either of these exposures. In human samples, 28% of individuals with laboratory‐confirmed influenza were seropositive for H1N1pdm09 NS1, whereas vaccinated cases and controls were seronegative. There was a trend for H1N1pdm09 NS1 seropositive cases reporting more severe and longer duration of symptomatic illness than seronegative cases. Anti‐HA H1N1pdm09 antibodies were detected in all cases and in 61% of controls.

Conclusions

The LIPS method could differentiate between sera from experimentally infected and vaccinated animals. However, in human samples obtained more than 6 months after the pandemic, LIPS was specific, but not sufficiently sensitive for ascertaining cases by exposure.

Epidemiology and Relative Severity of Influenza Subtypes in Singapore in the Post-Pandemic Period from 2009 to 2010

Background

After 2009, pandemic influenza A(H1N1) [A(H1N1)pdm09] cocirculated with A(H3N2) and B in Singapore.

Methods

A cohort of 760 participants contributed demographic data and up to 4 blood samples each from October 2009 to September 2010. We compared epidemiology of the 3 subtypes and investigated evidence for heterotypic immunity through multivariable logistic regression using a generalized estimating equation. To examine age-related differences in severity between subtypes, we used LOESS (locally weighted smoothing) plots of hospitalization to infection ratios and explored birth cohort effects referencing the pandemic years (1957; 1968).

Results

Having more household members aged 5–19 years and frequent public transport use increased risk of infection, while preexisting antibodies against the same subtype (odds ratio [OR], 0.61; P = .002) and previous influenza infection against heterotypic infections (OR, 0.32; P = .045) were protective. A(H1N1)pdm09 severity peaked in those born around 1957, while A(H3N2) severity was least in the youngest individuals and increased until it surpassed A(H1N1)pdm09 in those born in 1952 or earlier. Further analysis showed that severity of A(H1N1)pdm09 was less than that for A(H3N2) in those born in 1956 or earlier (P = .021) and vice versa for those born in 1968 or later (P < .001), with no difference in those born between 1957 and 1967 (P = .632).

Conclusions

Our findings suggest that childhood exposures had long-term impact on immune responses consistent with the theory of antigenic sin. This, plus observations on short-term cross-protection, have implications for vaccination and influenza epidemic and pandemic mitigation strategies.

NS Segment of a 1918 Influenza A Virus-Descendent Enhances Replication of H1N1pdm09 and Virus-Induced Cellular Immune Response in Mammalian and Avian Systems

The 2009 pandemic influenza A virus (IAV) H1N1 strain (H1N1pdm09) has widely spread and is circulating in humans and swine together with other human and avian IAVs. This fact raises the concern that reassortment between H1N1pdm09 and co-circulating viruses might lead to an increase of H1N1pdm09 pathogenicity in different susceptible host species. Herein, we explored the potential of different NS segments to enhance the replication dynamics, pathogenicity and host range of H1N1pdm09 strain A/Giessen/06/09 (Gi-wt). The NS segments were derived from (i) human H1N1- and H3N2 IAVs, (ii) highly pathogenic- (H5- or H7-subtypes) or (iii) low pathogenic avian influenza viruses (H7- or H9-subtypes). A significant increase of growth kinetics in A549 (human lung epithelia) and NPTr (porcine tracheal epithelia) cells was only noticed in vitro for the reassortant Gi-NS-PR8 carrying the NS segment of the 1918-descendent A/Puerto Rico/8/34 (PR8-wt, H1N1), whereas all other reassortants showed either reduced or comparable replication efficiencies. Analysis using ex vivo tracheal organ cultures of turkeys (TOC-Tu), a species susceptible to IAV H1N1 infection, demonstrated increased replication of Gi-NS-PR8 compared to Gi-wt. Also, Gi-NS-PR8 induced a markedly higher expression of immunoregulatory and pro-inflammatory cytokines, chemokines and interferon-stimulated genes in A549 cells, THP-1-derived macrophages (dHTP) and TOC-Tu. In vivo, Gi-NS-PR8 induced an earlier onset of mortality than Gi-wt in mice, whereas, 6-week-old chickens were found to be resistant to both viruses. These data suggest that the specific characteristics of the PR8 NS segments can impact on replication, virus induced cellular immune responses and pathogenicity of the H1N1pdm09 in different avian and mammalian host species.

Protective effect of a polyvalent influenza DNA vaccine in pigs

BACKGROUND

Influenza A virus in swine herds represents a major problem for the swine industry and poses a constant threat for the emergence of novel pandemic viruses and the development of more effective influenza vaccines for pigs is desired. By optimizing the vector backbone and using a needle-free delivery method, we have recently demonstrated a polyvalent influenza DNA vaccine that induces a broad immune response, including both humoral and cellular immunity.

OBJECTIVES

To investigate the protection of our polyvalent influenza DNA vaccine approach in a pig challenge study.

METHODS

By intradermal needle-free delivery to the skin, we immunized pigs with two different doses (500μg and 800μg) of an influenza DNA vaccine based on six genes of pandemic origin, including internally expressed matrix and nucleoprotein and externally expressed hemagglutinin and neuraminidase as previously demonstrated. Two weeks following immunization, the pigs were challenged with the 2009 pandemic H1N1 virus.

RESULTS

When challenged with 2009 pandemic H1N1, 0/5 vaccinated pigs (800μg DNA) became infected whereas 5/5 unvaccinated control pigs were infected. The pigs vaccinated with the low dose (500μg DNA) were only partially protected. The DNA vaccine elicited binding-, hemagglutination inhibitory (HI) - as well as cross-reactive neutralizing antibody activity and neuraminidase inhibiting antibodies in the immunized pigs, in a dose-dependent manner.

CONCLUSION

The present data, together with the previously demonstrated immunogenicity of our influenza DNA vaccine, indicate that naked DNA vaccine technology provides a strong approach for the development of improved pig vaccines, applying realistic low doses of DNA and a convenient delivery method for mass vaccination.

Demographic and ecological risk factors for human influenza A virus infections in rural Indonesia

Background

Indonesia has the world's highest reported mortality for human infections with highly pathogenic avian influenza (HPAI) A(H5N1) virus. Indonesia is an agriculturally driven country where human‐animal mixing is common and provides a unique environment for zoonotic influenza A virus transmission.

Objectives

To identify potential demographic and ecological risk factors for human infection with seasonal influenza A viruses in rural Indonesia, a population‐based study was conducted in Cileunyi and Soreang subdistricts near Bandung in western Java from 2008 to 2011.

Methods

Passive influenza surveillance with RT‐PCR confirmation of influenza A viral RNA in respiratory specimens was utilized for case ascertainment. A population census and mapping were utilized for population data collection. The presence of influenza A(H3N2) and A(H1N1)pdm09 virus infections in a household was modeled using Generalized Estimating Equations.

Results

Each additional child aged <5 years in a household increased the odds of H3N2 approximately 5 times (OR=4.59, 95%CI: 3.30‐6.24) and H1N1pdm09 by 3.5 times (OR=3.53, 95%CI: 2.51‐4.96). In addition, the presence of 16‐30 birds in the house was associated with an increased odds of H3N2 (OR=5.08, 95%CI: 2.00‐12.92) and H1N1pdm09 (OR=12.51 95%CI: 6.23‐25.13).

Conclusion

Our findings suggest an increase in influenza A virus infections in rural Indonesian households with young children and poultry.

Sequence analysis of haemagglutinin and neuraminidase of H1N1 strain from a patient coinfected with Mycobacterium tuberculosis

The 2009 H1N1 pandemic (H1N1pdm09) was associated with a considerable influenza-related morbidity and mortality. Among the complications, Mycobacterial tuberculosis was recorded as a coinfection with influenza in rare cases. The full-length sequences of the viral haemagglutinin and neuraminidase of H1N1pdm09 influenza A virus were analyzed from a recently infected patient. The patient was chronically infected with Mycobacterium tuberculosis. Molecular modelling and in-silico docking of the virus, and other selected strains with the drug oseltamivir were conducted and compared. Sequence analysis of the viral haemagglutinin revealed it to be closely related to the 6B.1 clade, with high identity to the circulating H1N1pdm09 strains, and confirmed that the virus still harbouring high affinity to the α-2,6-sialic acid human receptor. The viral neuraminidase showed high identity to the neuraminidase of the recently circulating strains of the virus with no evidence of the development of oseltamivir-resistant mutants. Regular monitoring of the circulating strains is recommended to screen for a possible emergence of drug-resistant strains.

Triple-reassortant influenza A virus with H3 of human seasonal origin, NA of swine origin, and internal A(H1N1) pandemic 2009 genes is established in Danish pigs

This report describes a triple‐reassortant influenza A virus with a HA that resembles H3 of human seasonal influenza from 2004 to 2005, N2 from influenza A virus already established in swine, and the internal gene cassette from A(H1N1)pdm09 has spread in Danish pig herds. The virus has been detected in several Danish pig herds during the last 2‐3 years and may possess a challenge for human as well as animal health.

Association of vaccine handling conditions with effectiveness of live attenuated influenza vaccine against H1N1pdm09 viruses in the United States

PURPOSE

This analysis examined potential causes of the lack of vaccine effectiveness (VE) of live attenuated influenza vaccine (LAIV) against A/H1N1pdm09 viruses in the United States (US) during the 2013-2014 season. Laboratory studies have demonstrated reduced thermal stability of A/California/07/2009, the A/H1N1pdm09 strain utilized in LAIV from 2009 through 2013-2014.

METHODS

Post hoc analyses of a 2013-2014 test-negative case-control (TNCC) effectiveness study investigated associations between vaccine shipping conditions and LAIV lot effectiveness. Investigational sites provided the LAIV lot numbers administered to each LAIV recipient enrolled in the study, and the vaccine distributor used by the site for commercially purchased vaccine. Additionally, a review was conducted of 2009-2014 pediatric observational TNCC effectiveness studies of LAIV, summarizing effectiveness by type/subtype, season, and geographic location.

RESULTS

From the 2013 to 2014 TNCC study, the proportion of LAIV recipients who tested positive for H1N1pdm09 was significantly higher among children who received a lot released between August 1 and September 15, 2013, compared with a lot shipped either earlier or later (21% versus 4%; P<0.01). A linear relationship was observed between the proportion of subjects testing positive for H1N1pdm09 and outdoor temperatures during truck unloading at distributors' central locations. The review of LAIV VE studies showed that in the 2010-2011 and 2013-2014 influenza seasons, no significant effectiveness of LAIV against H1N1pdm09 was demonstrated for the trivalent or quadrivalent formulations of LAIV in the US, respectively, in contrast to significant effectiveness against A/H3N2 and B strains during 2010-2014.

CONCLUSIONS

This study showed that the lack of VE observed with LAIV in the US against H1N1pdm09 viruses was associated with exposure of some LAIV lots to temperatures above recommended storage conditions during US distribution, and is likely explained by the increased susceptibility of the A/California/7/2009 (H1N1pdm09) LAIV strain to thermal degradation.

CLINICAL TRIAL REGISTRY

NCT01997450.

CD8 T cells and dendritic cells: key players in the attenuated maternal immune response to influenza infection

Pregnancy provides a unique challenge for maternal immunity, requiring the ability to tolerate the presence of a semi-allogeneic foetus, and yet still being capable of inducing an immune response against invading pathogens. To achieve this, numerous changes must occur in the activity and function of maternal immune cells throughout the course of pregnancy. Respiratory viruses take advantage of these changes, altering the sensitive balance of maternal immunity, leaving the mother with increased susceptibility to viral infections and increased disease severity. Influenza virus is one of the most common respiratory virus infections during pregnancy, leading to an increased risk of ICU hospitalisations, pneumonia, acute respiratory distress syndrome and even death. Whilst much research has been performed to understand the changes that must take place in maternal immunity during pregnancy, considerable work is still needed to fully comprehend this tremendous feat. To date, few studies have focused on the alterations that occur in maternal immunity during respiratory virus infections. This review highlights the role of dendritic cells (DCs) and CD8 T cells during pregnancy, and the changes that occur in these antiviral cells following influenza virus infections.

Excess mortality impact of two epidemics of pandemic influenza A(H1N1pdm09) virus in Hong Kong

Hong Kong experienced two large epidemics of pandemic influenza A(H1N1pdm09). We used regression methods to estimate the excess mortality associated with each epidemic. The first epidemic of H1N1pdm09 peaked in September 2009 and was associated with 2·13 [95% confidence interval (CI): -8·08, 11·82] excess all-cause deaths per 100 000 population. The second epidemic of H1N1pdm09 in early 2011 was associated with 4·72 [95% CI: -0·70, 10·50] excess deaths per 100 000 population. More than half of the estimated excess all-cause deaths were attributable to respiratory causes in each epidemic. The reasons for substantial impact in the second wave remain to be clarified.

Factors influencing infection by pandemic influenza A(H1N1)pdm09 over three epidemic waves in Singapore

Introduction

Previous influenza pandemics had second and on occasion third waves in many countries that were at times more severe than the initial pandemic waves.

Objective

This study aims to determine the seroepidemiology of successive waves of H1N1pdm09 infections in Singapore and the overall risks of infection.

Methods

We performed a cohort study amongst 838 adults, with blood samples provided upon recruitment and at 5 points from 2009 to 2011 and tested by haemagglutination inhibition (HI) with A/California/7/2009 (H1N1pdm09). Surveys on key demographic and clinical information were conducted at regular intervals, and associations between seroconversion and these variables were investigated.

Results

After the initial wave from June to September 2009, second and third waves occurred from November 2009 to February 2010 and April to June 2010, respectively. Seroconversion was 13·5% during the first wave and decreased to 6·2% and 6·8% in subsequent waves. Across the three waves, the elderly and those with higher starting HI titres were at lower risk of seroconversion, while those with larger households were at greater risk. Those with higher starting HI titres were also less likely to have an acute respiratory infection.

Conclusions

The second and third waves in Singapore had lower serological attack rates than the first wave. The elderly and those with higher HI titres had lower risk, while those in larger households had higher risk of seroconversion.