The role of nasal IgA in children vaccinated with live attenuated influenza vaccine

Induction of Superior Systemic and Mucosal Protective Immunity to SARS-CoV-2 by Nasal Administration of a VSV-ΔG-Spike Vaccine

The emergence of rapidly spreading variants of Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) poses a major challenge to vaccines' protective efficacy. Intramuscular (IM) vaccine administration induces short-lived immunity but does not prevent infection and transmission. New vaccination strategies are needed to extend the longevity of vaccine protection, induce mucosal and systemic immunity and prevent viral transmission. The intranasal (IN) administration of the VSV-ΔG-spike vaccine candidate directly to mucosal surfaces yielded superior mucosal and systemic immunity at lower vaccine doses. Compared to IM vaccination in the K18-hACE2 model, IN vaccination preferentially induced mucosal IgA and T-cells, reduced the viral load at the site of infection, and ameliorated disease-associated brain gene expression. IN vaccination was protective even one year after administration. As most of the world population has been vaccinated by IM injection, we demonstrate the potential of a heterologous IM + IN vaccination regimen to induce mucosal immunity while maintaining systemic immunity. Furthermore, the IM + IN regimen prevented virus transmission in a golden Syrian hamster co-caging model. Taken together, we show that IN vaccination with VSV-ΔG-spike, either as a homologous IN + IN regimen or as a boost following IM vaccination, has a favorable potential over IM vaccination in inducing efficient mucosal immunity, long-term protection and preventing virus transmission.

Unmasking the potential of secretory IgA and its pivotal role in protection from respiratory viruses

Mucosal immunity has regained its spotlight amidst the ongoing Coronavirus disease 19 (COVID-19) pandemic, with numerous studies highlighting the crucial role of mucosal secretory IgA (SIgA) in protection against Severe acute respiratory syndrome coronavirus-2 or SARS-CoV-2 infections. The observed limitations in the efficacy of currently authorized COVID-19 vaccines in inducing effective mucosal immune responses remind us of the limitations of systemic vaccination in promoting protective mucosal immunity. This resurgence of interest has motivated the development of vaccine platforms capable of enhancing mucosal responses, specifically the SIgA response, and the development of IgA-based therapeutics. Recognizing viral respiratory infections as a global threat, we would like to comprehensively review the existing knowledge on mucosal immunity, with a particular emphasis on SIgA, in the context of SARS-CoV-2, influenza, and Respiratory Syncytial Virus (RSV) infections. This review aims to describe the structural and functional specificities of SIgA, along with its nuanced role in combating influenza, RSV, and SARS-CoV-2 infections. Subsequent sections further elaborate promising vaccine strategies, including mucosal vaccines against Influenza, RSV, and SARS-CoV-2 respiratory viruses, currently undergoing preclinical and clinical development. Additionally, we address the challenges associated with mucosal vaccine development, concluding with a discussion on IgA-based therapeutics as a promising platform for the treatment of viral respiratory infections. This comprehensive review not only synthesizes current insights into mucosal immunity but also identifies critical knowledge gaps, strengthening the way for further advancements in our current understanding and approaches to combat respiratory viral threats.

A Next-Generation Adenoviral Vaccine Elicits Mucosal and Systemic Immunogenicity and Reduces Viral Shedding after SARS-CoV-2 Challenge in Nonhuman Primates

As new SARS-CoV-2 variants continue to emerge and impact communities worldwide, next-generation vaccines that enhance protective mucosal immunity may have a significant impact on productive infection and transmission. We have developed recombinant non-replicating adenovirus serotype 5 (rAd5) vaccines delivered by mucosal administration that express both target antigen and a novel molecular adjuvant within the same cell. Here, we describe the immunogenicity of three unique SARS-CoV-2 rAd5 vaccine candidates and their efficacy following viral challenge in non-human primates (NHPs). Intranasal immunization with rAd5 vaccines expressing Wuhan, or Beta variant spike alone, or Wuhan spike and nucleocapsid elicited strong antigen-specific serum IgG and IgA with neutralizing activity against multiple variants of concern (VOC). Robust cross-reactive mucosal IgA was detected after a single administration of rAd5, which showed strong neutralizing activity against multiple VOC. Additionally, mucosal rAd5 vaccination increased spike-specific IFN-γ producing circulating T-cells. Upon Beta variant SARS-CoV-2 challenge, all the vaccinated NHPs exhibited significant reductions in viral load and infectious particle shedding in both the nasal passages and lower airways. These findings demonstrate that mucosal rAd5 immunization is highly immunogenic, confers protective cross-reactive antibody responses in the circulation and mucosa, and reduces viral load and shedding after SARS-CoV-2 challenge.

Development of Cross-Reactive Live Attenuated Influenza Vaccine Candidates against Both Lineages of Influenza B Virus

BACKGROUND

Influenza viruses continue to cause a significant social and economic burden globally. Vaccination is recognized as the most effective measure to control influenza. Live attenuated influenza vaccines (LAIVs) are an effective means of preventing influenza, especially among children. A reverse genetics (RG) system is required to rapidly update the antigenic composition of vaccines, as well as to design LAIVs with a broader spectrum of protection. Such a system has been developed for the Russian LAIVs only for type A strains, but not for influenza B viruses (IBV).

METHODS

All genes of the B/USSR/60/69 master donor virus (B60) were cloned into RG plasmids, and the engineered B60, as well as a panel of IBV LAIV reassortants were rescued from plasmid DNAs encoding all viral genes. The engineered viruses were evaluated in vitro and in a mouse model.

RESULTS

The B60 RG system was successfully developed, which made it possible to rescue LAIV reassortants with the desired antigenic composition, including hybrid strains with hemagglutinin and neuraminidase genes belonging to the viruses from different IBV lineages. The LAIV candidate carrying the HA of the B/Victoria-lineage virus and NA from the B/Yamagata-lineage virus demonstrated optimal characteristics in terms of safety, immunogenicity and cross-protection, prompting its further assessment as a broadly protective component of trivalent LAIV.

CONCLUSIONS

The new RG system for B60 MDV allowed the rapid generation of type B LAIV reassortants with desired genome compositions. The generation of hybrid LAIV reassortants with HA and NA genes belonging to the opposite IBV lineages is a promising approach for the development of IBV vaccines with broad cross-protection.

Oral delivery of a chitosan adjuvanted COVID-19 vaccine provides long-lasting and broad-spectrum protection against SARS-CoV-2 variants of concern in golden hamsters

Coronavirus disease 2019 (COVID-19) seriously threatens public health safety and the global economy, which warrant effective prophylactic and therapeutic approaches. Currently, vaccination and establishment of immunity have significantly reduced the severity and mortality of COVID-19. However, in regard to COVID-19 vaccines, the broad-spectrum protective efficacy against SARS-CoV-2 variants and the blocking of virus transmission need to be further improved. In this study, an optimum oral COVID-19 vaccine candidate, rVSVΔG-Sdelta, was selected from a panel of vesicular stomatitis virus (VSV)-based constructs bearing spike proteins from different SARS-CoV-2 strains. After chitosan modification, rVSVΔG-Sdelta induced both local and peripheral antibody response, particularly, broad-spectrum and long-lasting neutralizing antibodies against SARS-CoV-2 persisted for 1 year. Cross-protection against SARS-CoV-2 WT, Beta, Delta, BA.1, and BA.2 strains was achieved in golden hamsters, which presented as significantly reduced viral replication in the respiratory tract and alleviated pulmonary pathology post SARS-CoV-2 challenge. Overall, this study provides a convenient, oral-delivered, and effective oral mucosal vaccine against COVID-19, which would supplement pools and facilitate the distribution of COVID-19 vaccines.

Clade 2.3.4.4 H5 chimeric cold-adapted attenuated influenza vaccines induced cross-reactive protection in mice and ferrets

IMPORTANCE

Clade 2.3.4.4 H5Nx avian influenza viruses (AIVs) have circulated globally and caused substantial economic loss. Increasing numbers of humans have been infected with Clade 2.3.4.4 H5N6 AIVs in recent years. Only a few human influenza vaccines have been licensed to date. However, the licensed live attenuated influenza virus vaccine exhibited the potential of being recombinant with the wild-type influenza A virus (IAV). Therefore, we developed a chimeric cold-adapted attenuated influenza vaccine based on the Clade 2.3.4.4 H5 AIVs. These H5 vaccines demonstrate the advantage of being non-recombinant with circulated IAVs in the future influenza vaccine study. The findings of our current study reveal that these H5 vaccines can induce cross-reactive protective efficacy in mice and ferrets. Our H5 vaccines may provide a novel option for developing human-infected Clade 2.3.4.4 H5 AIV vaccines.

Mucosal Adenoviral-vectored Vaccine Boosting Durably Prevents XBB.1.16 Infection in Nonhuman Primates

Waning immunity and continued virus evolution have limited the durability of protection from symptomatic infection mediated by intramuscularly (IM)-delivered mRNA vaccines against COVID-19 although protection from severe disease remains high. Mucosal vaccination has been proposed as a strategy to increase protection at the site of SARS-CoV-2 infection by enhancing airway immunity, potentially reducing rates of infection and transmission. Here, we compared protection against XBB.1.16 virus challenge 5 months following IM or mucosal boosting in non-human primates (NHP) that had previously received a two-dose mRNA-1273 primary vaccine regimen. The mucosal boost was composed of a bivalent chimpanzee adenoviral-vectored vaccine encoding for both SARS-CoV-2 WA1 and BA.5 spike proteins (ChAd-SARS-CoV-2-S) and delivered either by an intranasal mist or an inhaled aerosol. An additional group of animals was boosted by the IM route with bivalent WA1/BA.5 spike-matched mRNA (mRNA-1273.222) as a benchmark control. NHP were challenged in the upper and lower airways 18 weeks after boosting with XBB.1.16, a heterologous Omicron lineage strain. Cohorts boosted with ChAd-SARS-CoV-2-S by an aerosolized or intranasal route had low to undetectable virus replication as assessed by levels of subgenomic SARS-CoV-2 RNA in the lungs and nose, respectively. In contrast, animals that received the mRNA-1273.222 boost by the IM route showed minimal protection against virus replication in the upper airway but substantial reduction of virus RNA levels in the lower airway. Immune analysis showed that the mucosal vaccines elicited more durable antibody and T cell responses than the IM vaccine. Protection elicited by the aerosolized vaccine was associated with mucosal IgG and IgA responses, whereas protection elicited by intranasal delivery was mediated primarily by mucosal IgA. Thus, durable immunity and effective protection against a highly transmissible heterologous variant in both the upper and lower airways can be achieved by mucosal delivery of a virus-vectored vaccine. Our study provides a template for the development of mucosal vaccines that limit infection and transmission against respiratory pathogens.

Graphical abstract

An easy pill to swallow: oral recombinant vaccines for the 21st century

Oral vaccines have a distinctive advantage of stimulating immune responses in the mucosa, where numerous pathogens gain entry and cause disease. Although various efforts have been attempted to create recombinant mucosal vaccines that provoke strong immunogenicity, the outcomes in clinical trials have been weak or inconsistent. Therefore, next-generation mucosal vaccines are needed that are more immunogenic. Here, we discuss oral vaccines with an emphasis on a next-generation mucosal vaccine that utilizes a nonreplicating human recombinant adenovirus type-5 (rAd5) vector. Numerous positive clinical results investigating oral rAd5 vaccines are reviewed, with a summary of the immunogenicity and efficacy results for specific vaccine indications of influenza, norovirus, and SARS-CoV-2. The determination of correlates of protection for oral vaccination and the potential impact this novel vaccine formulation may have on disease transmission are also discussed. In summary, successful oral vaccination can be accomplished and would have major public health benefits if approved.

Role of Acacia catechu and Scutellaria baicalensis in Enhancing Immune Function Following Influenza Vaccination of Healthy Adults: A Randomized, Triple-Blind, Placebo-Controlled Clinical Trial

OBJECTIVE

The study aimed to examine the role of an Acacia catechu and Scutellaria baicalensis formulation, UP446, on supporting immune function in response to influenza vaccination.

METHODS

A randomized, triple-blind, placebo-controlled, parallel study consisted of a 56-day intervention period with a 28-day pre-vaccination period, an influenza vaccination on Day 28 and 28-day post-vaccination period. Fifty healthy adults 40-80 years of age who had not received their flu vaccine were randomized to either UP446 or Placebo. At baseline, Days 28 and 56, immune and oxidative stress markers were measured in blood and a quality of life questionnaire was administered. Participants completed the Wisconsin Upper Respiratory Symptom Survey (WURSS)-24 daily.

RESULTS

In the post-vaccination period, total IgA and IgG levels increased in participants supplemented with UP446 vs. those on Placebo (p ≤ 0.026). As well, influenza B-specific IgG increased 19.4% from Day 28 to 56 and 11.6% from baseline at Day 56 (p ≤ 0.0075). Serum glutathione peroxidase (GSH-Px) was increased in the pre-vaccination period and from baseline at Day 56 with UP446 supplementation (p ≤ 0.0270).

CONCLUSION

These results suggest a 56-day supplementation with UP446 was beneficial in mounting a robust humoral response following vaccination. Increasing GSH-Px in the pre-vaccination period may help improve antioxidant functions and potentially mitigate the oxidative stress induced following vaccination.

Viral vectored vaccines: design, development, preventive and therapeutic applications in human diseases

Human diseases, particularly infectious diseases and cancers, pose unprecedented challenges to public health security and the global economy. The development and distribution of novel prophylactic and therapeutic vaccines are the prioritized countermeasures of human disease. Among all vaccine platforms, viral vector vaccines offer distinguished advantages and represent prominent choices for pathogens that have hampered control efforts based on conventional vaccine approaches. Currently, viral vector vaccines remain one of the best strategies for induction of robust humoral and cellular immunity against human diseases. Numerous viruses of different families and origins, including vesicular stomatitis virus, rabies virus, parainfluenza virus, measles virus, Newcastle disease virus, influenza virus, adenovirus and poxvirus, are deemed to be prominent viral vectors that differ in structural characteristics, design strategy, antigen presentation capability, immunogenicity and protective efficacy. This review summarized the overall profile of the design strategies, progress in advance and steps taken to address barriers to the deployment of these viral vector vaccines, simultaneously highlighting their potential for mucosal delivery, therapeutic application in cancer as well as other key aspects concerning the rational application of these viral vector vaccines. Appropriate and accurate technological advances in viral vector vaccines would consolidate their position as a leading approach to accelerate breakthroughs in novel vaccines and facilitate a rapid response to public health emergencies.

Age-dependent nasal immune responses in non-hospitalized bronchiolitis children

Bronchiolitis in children is associated with significant rates of morbidity and mortality. Many studies have been performed using samples from hospitalized bronchiolitis patients, but little is known about the immunological responses from infants suffering from mild/moderate bronchiolitis that do not require hospitalization. We have studied a collection of nasal lavage fluid (NLF) samples from outpatient bronchiolitis children as a novel strategy to unravel local humoral and cellular responses, which are not fully characterized. The children were age-stratified in three groups, two of them (GI under 2-months, GII between 2-4 months) presenting a first episode of bronchiolitis, and GIII (between 4 months and 2 years) with recurrent respiratory infections. Here we show that elevated levels of pro-inflammatory cytokines (IL1β, IL6, TNFα, IL18, IL23), regulatory cytokines (IL10, IL17A) and IFNγ were found in the three bronchiolitis cohorts. However, little or no change was observed for IL33 and MCP1, at difference to previous results from bronchiolitis hospitalized patients. Furthermore, our results show a tendency to IL1β, IL6, IL18 and TNFα increased levels in children with mild pattern of symptom severity and in those in which non RSV respiratory virus were detected compared to RSV+ samples. By contrast, no such differences were found based on gender distribution. Bronchiolitis NLFs contained more IgM, IgG1, IgG3 IgG4 and IgA than NLF from their age-matched healthy controls. NLF from bronchiolitis children predominantly contained neutrophils, and also low frequency of monocytes and few CD4⁺ and CD8⁺ T cells. NLF from infants older than 4-months contained more intermediate monocytes and B cell subsets, including naïve and memory cells. BCR repertoire analysis of NLF samples showed a biased VH1 usage in IgM repertoires, with low levels of somatic hypermutation. Strikingly, algorithmic studies of the mutation profiles, denoted antigenic selection on IgA-NLF repertoires. Our results support the use of NLF samples to analyze immune responses and may have therapeutic implications.

Development and function of tissue-resident memory B cells

Barrier tissues are the primary site of infection for pathogens likely to cause future pandemics. Tissue-resident lymphocytes can rapidly detect pathogens upon infection of barrier tissues and are critical in preventing viral spread. However, most vaccines fail to induce tissue-resident lymphocytes and are instead reliant on circulating antibodies to mediate protective immunity. Circulating antibody titers wane over time following vaccination leaving individuals susceptible to breakthrough infections by variant viral strains that evade antibody neutralization. Memory B cells were recently found to establish tissue residence following infection of barrier tissues. Here, we summarize emerging evidence for the importance of tissue-resident memory B cells in the establishment of protective immunity against viral and bacterial challenge. We also discuss the role of tissue-resident memory B cells in regulating the progression of non-infectious diseases. Finally, we examine new approaches to develop vaccines capable of eliciting barrier immunity.

Development and characterization of influenza M2 ectodomain and/or hemagglutinin stalk-based dendritic cell-targeting vaccines

A universal influenza vaccine is required for broad protection against influenza infection. Here, we revealed the efficacy of novel influenza vaccine candidates based on Ebola glycoprotein dendritic cell (DC)-targeting domain (EΔM) fusion protein technology. The four copies of ectodomain matrix protein of influenza (tM2e) or M2e hemagglutinin stalk (HA stalk) peptides (HM2e) were fused with EΔM to generate EΔM-tM2e or EΔM-HM2e, respectively. We demonstrated that EΔM-HM2e- or EΔM-tM2e-pseudotyped viral particles can efficiently target DC/macrophages in vitro and induced significantly high titers of anti-HA and/or anti-M2e antibodies in mice. Significantly, the recombinant vesicular stomatitis virus (rVSV)-EΔM-tM2e and rVSV-EΔM-HM2e vaccines mediated rapid and potent induction of M2 or/and HA antibodies in mice sera and mucosa. Importantly, vaccination of rVSV-EΔM-tM2e or rVSV-EΔM-HM2e protected mice from influenza H1N1 and H3N2 challenges. Taken together, our study suggests that rVSV-EΔM-tM2e and rVSV-EΔM-HM2e are promising candidates that may lead to the development of a universal vaccine against different influenza strains.

Towards the future exploration of mucosal mRNA vaccines against emerging viral diseases; lessons from existing next-generation mucosal vaccine strategies

The mRNA vaccine platform has offered the greatest potential in fighting the COVID-19 pandemic owing to rapid development, effectiveness, and scalability to meet the global demand. There are many other mRNA vaccines currently being developed against different emerging viral diseases. As with the current COVID-19 vaccines, these mRNA-based vaccine candidates are being developed for parenteral administration via injections. However, most of the emerging viruses colonize the mucosal surfaces prior to systemic infection making it very crucial to target mucosal immunity. Although parenterally administered vaccines would induce a robust systemic immunity, they often provoke a weak mucosal immunity which may not be effective in preventing mucosal infection. In contrast, mucosal administration potentially offers the dual benefit of inducing potent mucosal and systemic immunity which would be more effective in offering protection against mucosal viral infection. There are however many challenges posed by the mucosal environment which impede successful mucosal vaccination. The development of an effective delivery system remains a major challenge to the successful exploitation of mucosal mRNA vaccination. Nonetheless, a number of delivery vehicles have been experimentally harnessed with different degrees of success in the mucosal delivery of mRNA vaccines. In this review, we provide a comprehensive overview of mRNA vaccines and summarise their application in the fight against emerging viral diseases with particular emphasis on COVID-19 mRNA platforms. Furthermore, we discuss the prospects and challenges of mucosal administration of mRNA-based vaccines, and we explore the existing experimental studies on mucosal mRNA vaccine delivery.

Drop the Needle; A Temperature Stable Oral Tablet Vaccine Is Protective against Respiratory Viral Pathogens

To effectively combat emerging infections and prevent future pandemics, next generation vaccines must be developed quickly, manufactured rapidly, and most critically, administered easily. Next generation vaccines need innovative approaches that prevent infection, severe disease, and reduce community transmission of respiratory pathogens such as influenza and SARS-CoV-2. Here we review an oral vaccine tablet that can be manufactured and released in less than 16 weeks of antigen design and deployed without the need for cold chain. The oral Ad5 modular vaccine platform utilizes a non-replicating adenoviral vector (rAd5) containing a novel molecular TLR3 adjuvant that is delivered by tablet, not by needle. This enterically coated, room temperature-stable vaccine tablet elicits robust antigen-specific IgA in the gastrointestinal and respiratory tracts and upregulates mucosal homing adhesion molecules on circulating B and T cells. Several influenza antigens have been tested using this novel vaccine approach and demonstrated efficacy in both preclinical animal models and in phase I/II clinical trials, including in a human challenge study. This oral rAd5 vaccine platform technology offers a promising new avenue for aiding in rapid pandemic preparedness and equitable worldwide vaccine distribution.

Mucosal Antibody Response to SARS-CoV-2 in Paediatric and Adult Patients: A Longitudinal Study

Background: SARS-CoV-2 enters the body through inhalation or self-inoculation to mucosal surfaces. The kinetics of the ocular and nasal mucosal-specific-immunoglobulin A(IgA) responses remain under-studied. Methods: Conjunctival fluid (CF, n = 140) and nasal epithelial lining fluid (NELF, n = 424) obtained by paper strips and plasma (n = 153) were collected longitudinally from SARS-CoV-2 paediatric (n = 34) and adult (n = 47) patients. The SARS-CoV-2 spike protein 1(S1)-specific mucosal antibody levels in COVID-19 patients, from hospital admission to six months post-diagnosis, were assessed. Results: The mucosal antibody was IgA-predominant. In the NELF of asymptomatic paediatric patients, S1-specific IgA was induced as early as the first four days post-diagnosis. Their plasma S1-specific IgG levels were higher than in symptomatic patients in the second week after diagnosis. The IgA and IgG levels correlated positively with the surrogate neutralization readout. The detectable NELF “receptor-blocking” S1-specific IgA in the first week after diagnosis correlated with a rapid decline in viral load. Conclusions: Early and intense nasal S1-specific IgA levels link to a rapid decrease in viral load. Our results provide insights into the role of mucosal immunity in SARS-CoV-2 exposure and protection. There may be a role of NELF IgA in the screening and diagnosis of SARS-CoV-2 infection.

Mucosal Vaccination With Recombinant Tm-WAP49 Protein Induces Protective Humoral and Cellular Immunity Against Experimental Trichuriasis in AKR Mice

Trichuriasis is one of the most common neglected tropical diseases of the world's poorest people. A recombinant vaccine composed of Tm-WAP49, an immunodominant antigen secreted by adult Trichuris stichocytes into the mucosa of the cecum to which the parasite attaches, is under development. The prototype is being evaluated in a mouse model of Trichuris muris infection, with the ultimate goal of producing a mucosal vaccine through intranasal delivery. Intranasal immunization of mice with Tm-WAP49 formulated with the adjuvant OCH, a truncated analog of alpha-GalCer with adjuvanticity to stimulate natural killer T cells (NKT) and mucosal immunity, induced significantly high levels of IgG and its subclasses (IgG1 and IgG2a) in immunized mice. This also resulted in a significant reduction of worm burden after challenge with T. muris-infective eggs. The addition of QS-21 adjuvant to this vaccine formulation further reduced worm counts. The improved protection from the dual-adjuvanted vaccine correlated with higher serum antibody responses (IgG, IgG1, IgG2a, IgA) as well as with the induction of antigen-specific IgA in the nasal mucosa. It was also associated with the robust cellular responses including functional subsets of CD4 T cells producing IL-4, and cytotoxic CD8 T cells expressing granzyme B. The worm reduction achieved by mucosal immunization was higher than that induced by subcutaneous immunization. Intranasal immunization also induced a significantly higher nasal mucosa-secreted antigen-specific IgA response, as well as higher functional cellular responses including CD4⁺IL4⁺ (Th1) and CD8⁺GnzB⁺ (Th2) T cells, and antigen-specific INFγ-producing T cells in both spleen and MLNs and antibody-producing B cells (CD19⁺B220⁺/B220⁺GL7⁺). Mucosal immunization further induced long-term T lymphocyte memory with increased central (CD62L⁺CD44⁺) and effector (CD62L^-CD44⁺) memory subsets of both CD4 and CD8 T cells at 60 days after the last immunization. In summary, intranasal immunization with recombinant Tm-WAP49 protein induced strong protection versus murine trichuriasis. It represents a promising vaccination approach against intestinal nematodes.

Safety, Immunogenicity, and Protective Efficacy of an H5N1 Chimeric Cold-Adapted Attenuated Virus Vaccine in a Mouse Model

H5N1 influenza virus is a threat to public health worldwide. The virus can cause severe morbidity and mortality in humans. We constructed an H5N1 influenza candidate virus vaccine from the A/chicken/Guizhou/1153/2016 strain that was recommended by the World Health Organization. In this study, we designed an H5N1 chimeric influenza A/B vaccine based on a cold-adapted (ca) influenza B virus B/Vienna/1/99 backbone. We modified the ectodomain of H5N1 hemagglutinin (HA) protein, while retaining the packaging signals of influenza B virus, and then rescued a chimeric cold-adapted H5N1 candidate influenza vaccine through a reverse genetic system. The chimeric H5N1 vaccine replicated well in eggs and the Madin-Darby Canine Kidney cells. It maintained a temperature-sensitive and cold-adapted phenotype. The H5N1 vaccine was attenuated in mice. Hemagglutination inhibition (HAI) antibodies, micro-neutralizing (MN) antibodies, and IgG antibodies were induced in immunized mice, and the mucosal IgA antibody responses were detected in their lung lavage fluids. The IFN-γ-secretion and IL-4-secretion by the mouse splenocytes were induced after stimulation with the specific H5N1 HA protein. The chimeric H5N1 candidate vaccine protected mice against lethal challenge with a wild-type highly pathogenic avian H5N1 influenza virus. The chimeric H5 candidate vaccine is thus a potentially safe, attenuated, and reassortment-incompetent vaccine with circulating A viruses.

Protective mucosal immunity against SARS-CoV-2 after heterologous systemic prime-mucosal boost immunization

Several effective SARS-CoV-2 vaccines are currently in use, but effective boosters are needed to maintain or increase immunity due to waning responses and the emergence of novel variants. Here we report that intranasal vaccinations with adenovirus 5 and 19a vectored vaccines following a systemic plasmid DNA or mRNA priming result in systemic and mucosal immunity in mice. In contrast to two intramuscular applications of an mRNA vaccine, intranasal boosts with adenoviral vectors induce high levels of mucosal IgA and lung-resident memory T cells (TRM); mucosal neutralization of virus variants of concern is also enhanced. The mRNA prime provokes a comprehensive T cell response consisting of circulating and lung TRM after the boost, while the plasmid DNA prime induces mostly mucosal T cells. Concomitantly, the intranasal boost strategies lead to complete protection against a SARS-CoV-2 infection in mice. Our data thus suggest that mucosal booster immunizations after mRNA priming is a promising approach to establish mucosal immunity in addition to systemic responses.

Cigarette smoke exposure attenuates the induction of antigen-specific IgA in the murine upper respiratory tract

The upper respiratory tract is highly exposed to airborne pathogens and serves as an important inductive site for protective antibody responses, including mucosal IgA and systemic IgG. However, it is currently unknown to what extent inhaled environmental toxins, such as a cigarette smoke, affect the ability to induce antibody-mediated immunity at this site. Using a murine model of intranasal lipopolysaccharide and ovalbumin (LPS/OVA) immunization, we show that cigarette smoke exposure compromises the induction of antigen-specific IgA in the upper airways and systemic circulation. Deficits in OVA-IgA were observed in conjunction with a reduced accumulation of OVA-specific IgA antibody-secreting cells (ASCs) in the nasal mucosa, inductive tissues (NALT, cervical lymph nodes, spleen) and the blood. Nasal OVA-IgA from smoke-exposed mice also demonstrated reduced avidity during the acute post-immunization period in association with an enhanced mutational burden in the cognate nasal Igha repertoire. Mechanistically, smoke exposure attenuated the ability of the nasal mucosa to upregulate VCAM-1 and pIgR, suggesting that cigarette smoke may inhibit both nasal ASC homing and IgA transepithelial transport. Overall, these findings demonstrate the immunosuppressive nature of tobacco smoke and illustrate the diversity of mechanisms through which this noxious stimulus can interfere with IgA-mediated immunity in the upper airways.

Live Attenuated Cold-Adapted Influenza Vaccines

Live attenuated, cold-adapted influenza vaccines exhibit several desirable characteristics, including the induction of systemic, mucosal, and cell-mediated immunity resulting in breadth of protection, ease of administration, and yield. Seasonal live attenuated influenza vaccines (LAIVs) were developed in the United States and Russia and have been used in several countries. In the last decade, following the incorporation of the 2009 pandemic H1N1 strain, the performance of both LAIVs has been variable and the U.S.-backbone LAIV was less effective than the corresponding inactivated influenza vaccines. The cause appears to be reduced replicative fitness of some H1N1pdm09 viruses, indicating a need for careful selection of strains included in multivalent LAIV formulations. Assays are now being implemented to select optimal strains. An improved understanding of the determinants of replicative fitness of vaccine strains and of vaccine effectiveness of LAIVs is needed for public health systems to take full advantage of these valuable vaccines.

IgA potentiates NETosis in response to viral infection

IgA is the second most abundant antibody present in circulation and is enriched at mucosal surfaces. As such, IgA plays a key role in protection against a variety of mucosal pathogens including viruses. In addition to neutralizing viruses directly, IgA can also stimulate Fc-dependent effector functions via engagement of Fc alpha receptors (Fc-αRI) expressed on the surface of certain immune effector cells. Neutrophils are the most abundant leukocyte, express Fc-αRI, and are often the first to respond to sites of injury and infection. Here, we describe a function for IgA-virus immune complexes (ICs) during viral infections. We show that IgA-virus ICs potentiate NETosis-the programmed cell-death pathway through which neutrophils release neutrophil extracellular traps (NETs). Mechanistically, IgA-virus ICs potentiated a suicidal NETosis pathway via engagement of Fc-αRI on neutrophils through a toll-like receptor-independent, NADPH oxidase complex-dependent pathway. NETs also were capable of trapping and inactivating viruses, consistent with an antiviral function.

Safety and Immunogenicity of a Novel Intranasal Influenza Vaccine (NasoVAX): A Phase 2 Randomized, Controlled Trial

Annual influenza vaccination greatly reduces morbidity and mortality, but effectiveness remains sub-optimal. Weaknesses of current vaccines include low effectiveness against mismatched strains, lack of mucosal and other effective tissue-resident immune responses, weak cellular immune responses, and insufficiently durable immune responses. The safety and immunogenicity of NasoVAX, a monovalent intranasal influenza vaccine based on a replication-deficient adenovirus type 5 platform, were evaluated in a placebo-controlled single ascending-dose study. Sixty healthy adults (18-49 years) received a single intranasal dose of 1×109 viral particles (vp), 1 × 1010 vp, or 1 × 1011 vp of NasoVAX or placebo. NasoVAX was well-tolerated and elicited robust influenza-specific systemic and mucosal immune responses. The highest NasoVAX dose and the approved Fluzone® influenza vaccine elicited comparable hemagglutination inhibition (HAI) geometric mean titers (152.8 vs. 293.4) and microneutralization (MN) geometric mean titers (142.5 vs. 162.8), with NasoVAX HAI titers maintained more than 1-year on average following a single dose. Hemagglutinin-specific T cells responses were also documented in peripheral mononuclear cell (PBMC) preparations. Consistent with the intranasal route of administration, NasoVAX elicited antigen-specific mucosal IgA responses in the nasopharyngeal cavity with an increase of approximately 2-fold over baseline GMT at the mid- and high-doses. In summary, NasoVAX appeared safe and elicited a broad immune response, including humoral, cellular, and mucosal immunity, with no impact of baseline anti-adenovirus antibody at the most immunogenic dose.

Influenza in Children

Influenza poses a significant disease burden on children worldwide, with high rates of hospitalization and substantial morbidity and mortality. Although the clinical presentation of influenza in children has similarities to that seen in adults, there are unique aspects to how children present with infection that are important to recognize. In addition, children play a significant role in viral transmission within communities. Growing evidence supports the idea that early influenza infection can uniquely establish lasting immunologic memory, making an understanding of how viral immunity develops in this population critical to better protect children from infection and to facilitate efforts to develop a more universally protective influenza vaccine.

Impact of Pre-Existing Immunity to Influenza on Live-Attenuated Influenza Vaccine (LAIV) Immunogenicity

During the previous influenza seasons, between 2010 and 2016, the live attenuated influenza vaccine (LAIV) provided variable efficacy against influenza in the U.S., causing the recommendation against the use of the LAIV. In striking contrast, pre-clinical studies have repeatedly demonstrated superior efficacy of LAIV against mismatched influenza viruses, compared to inactivated influenza vaccines (IIV). This disparity in reported vaccine efficacies between pre-clinical and clinical studies may in part be explained by limitations of the animal models of influenza. In particular, the absence of pre-existing immunity in animal models has recently emerged as a potential explanation for the discrepancies between preclinical findings and human studies. This commentary focuses on the potential impact of pre-existing immunity on LAIV induced immunogenicity with an emphasis on cross-protective immunity.

Live-Attenuated Influenza Vaccine Induces Tonsillar Follicular T Helper Cell Responses That Correlate With Antibody Induction

Background

Influenza remains a major threat to public health. Live-attenuated influenza vaccines (LAIV) have been shown to be effective, particularly in children. Follicular T helper (TFH) cells provide B-cell help and are crucial for generating long-term humoral immunity. However the role of TFH cells in LAIV-induced immune responses is unknown.

Methods

We collected tonsils, plasma, and saliva samples from children and adults receiving LAIV prior to tonsillectomy. We measured influenza-specific TFH-cell responses after LAIV by flow cytometry and immunohistochemistry. Systemic and local antibody responses were analysed by hemagglutination inhibition assay and enzyme-linked immunosorbent assay.

Results

We report that LAIV induced early (3–7 days post-vaccination) activation of tonsillar follicles and influenza-specific TFH-cell (CXCR5+CD57+CD4+ T cell) responses in children, and to a lesser extent in adults. Serological analyses showed that LAIV elicited rapid (day 14) and long-term (up to 1 year post-vaccination) antibody responses (hemagglutination inhibition, influenza-specific IgG) in children, but not adults. There was an inverse correlation between pre-existing influenza-specific salivary IgA concentrations and tonsillar TFH-cell responses, and a positive correlation between tonsillar TFH-cell and systemic IgG induction after LAIV.

Conclusions

Our data, taken together, demonstrate an important role of tonsillar TFH cells in LAIV-induced immunity in humans.

Prospects and Challenges in the Development of Universal Influenza Vaccines

Current influenza vaccines offer suboptimal protection and depend on annual reformulation and yearly administration. Vaccine technology has rapidly advanced during the last decade, facilitating development of next-generation influenza vaccines that can target a broader range of influenza viruses. The development and licensure of a universal influenza vaccine could provide a game changing option for the control of influenza by protecting against all influenza A and B viruses. Here we review important findings and considerations regarding the development of universal influenza vaccines and what we can learn from this moving forward with a SARS-CoV-2 vaccine design.

Seasonal and pandemic influenza: 100 years of progress, still much to learn

Influenza viruses are highly transmissible, both within and between host species. The severity of the disease they cause is highly variable, from the mild and inapparent through to the devastating and fatal. The unpredictability of epidemic and pandemic outbreaks is accompanied but the predictability of seasonal disease in wide areas of the Globe, providing an inexorable toll on human health and survival. Although there have been great improvements in understanding influenza viruses and the disease that they cause, our knowledge of the effects they have on the host and the ways that the host immune system responds continues to develop. This review highlights the importance of the mucosa in defence against infection and in understanding the pathogenesis of disease. Although vaccines have been available for many decades, they remain suboptimal in needing constant redesign and in only providing short-term protection. There are real prospects for improvement in treatment and prevention of influenza soon, based on deeper knowledge of how the virus transmits, replicates and triggers immune defences at the mucosal surface.

Immunogenicity Measures of Influenza Vaccines: A Study of 1164 Registered Clinical Trials

Influenza carries an enormous burden each year. Annual influenza vaccination is the best means of reducing this burden. To be clinically effective, influenza vaccines must be immunogenic, and several immunological assays to test their immunogenicity have been developed. This study aimed to describe the patterns of use of the various immunological assays available to measure the influenza vaccine-induced adaptive immune response and to determine its correlates of protection. A total of 76.5% of the studies included in our analysis measured only the humoral immune response. Among these, the hemagglutination-inhibition assay was by far the most widely used. Other, less common, humoral immune response assays were: virus neutralization (21.7%), enzyme-linked immunosorbent (10.1%), single radial hemolysis (4.6%), and assays able to quantify anti-neuraminidase antibodies (1.7%). By contrast, cell-mediated immunity was quantified in only 23.5% of studies. Several variables were significantly associated with the use of single assays. Specifically, some influenza vaccine types (e.g., adjuvanted, live attenuated and cell culture-derived or recombinant), study phase and study sponsorship pattern were usually found to be statistically significant predictors. We discuss the principal findings and make some suggestions from the point of view of the various stakeholders.

IgA Responses Following Recurrent Influenza Virus Vaccination

Influenza is a highly contagious viral respiratory disease that affects millions of people worldwide each year. Annual vaccination is recommended by the World Health Organization to reduce influenza severity and limit transmission through elicitation of antibodies targeting mainly the hemagglutinin glycoprotein of the influenza virus. Antibodies elicited by current seasonal influenza vaccines are predominantly strain-specific. However, continuous antigenic drift by circulating influenza viruses facilitates escape from pre-existing antibodies requiring frequent reformulation of the seasonal influenza vaccine. Traditionally, immunological responses to influenza vaccination have been largely focused on IgG antibodies, with almost complete disregard of other isotypes. In this report, young adults (18–34 years old) and elderly (65–85 years old) subjects were administered the split inactivated influenza vaccine for 3 consecutive seasons and their serological IgA and IgG responses were profiled. Moreover, correlation analysis showed a positive relationship between vaccine-induced IgA antibody titers and traditional immunological endpoints, exposing vaccine-induced IgA antibodies as an important novel immune correlate during influenza vaccination.

The Effects of Pre-Existing Antibodies on Live-Attenuated Viral Vaccines

Live-attenuated vaccines (LAVs) have achieved remarkable successes in controlling virus spread, as well as for other applications such as cancer immunotherapy. However, with rapid increases in international travel, globalization, geographic spread of viral vectors, and widespread use of vaccines, there is an increasing need to consider how pre-exposure to viruses which share similar antigenic regions can impact vaccine efficacy. Pre-existing antibodies, derived from either from maternal–fetal transmission, or by previous infection or vaccination, have been demonstrated to interfere with vaccine immunogenicity of measles, adenovirus, and influenza LAVs. Immune interference of LAVs can be caused by the formation of virus–antibody complexes that neutralize virus infection in antigen-presenting cells, or by the cross-linking of the B-cell receptor with the inhibitory receptor, FcγRIIB. On the other hand, pre-existing antibodies can augment flaviviral LAV efficacy such as that of dengue and yellow fever virus, especially when pre-existing antibodies are present at sub-neutralizing levels. The increased vaccine immunogenicity can be facilitated by antibody-dependent enhancement of virus infection, enhancing virus uptake in antigen-presenting cells, and robust induction of innate immune responses that promote vaccine immunogenicity. This review examines the literature on this topic and examines the circumstances where pre-existing antibodies can inhibit or enhance LAV efficacy. A better knowledge of the underlying mechanisms involved could allow us to better manage immunization in seropositive individuals and even identify possibilities that could allow us to exploit pre-existing antibodies to boost vaccine-induced responses for improved vaccine efficacy.

Breadth of Antibody Responses during Influenza Virus Infection and Vaccination

Influenza viruses are a major public health problem, causing severe respiratory diseases. Vaccines offer the effective protective strategy against influenza virus infection. However, the systemic and adaptive immune responses to infection and vaccination are quite different. Inactivated vaccines are the best available countermeasure to induce effective antibodies against the emerged virus, but the response is narrow compared with potential breadth of virus infection. There is solid evidence to indicate that antibody responses to natural infection are relatively broad and exhibit quite different immunodominance patterns. Furthermore, T follicular helper cells (T_FH) and germinal center (GC) responses play a central role in generating broad protective antibodies. In this review, we discuss recent advances on the contribution of T_FH and GC responses to the breadth of antibody responses.

Understanding Immunity in Children Vaccinated With Live Attenuated Influenza Vaccine

Live attenuated influenza vaccine (LAIV), or FluMist, was approved for use in the United States in 2003. This vaccine, administered intranasally, offers the advantage of stimulating immunity at the site of infection in the upper respiratory tract and, by mimicking natural infection, has the potential to elicit a multifaceted immune response. However, the development of immunity following LAIV administration requires viral replication, causing vaccine effectiveness to be impacted by both the replicative fitness of the attenuated viruses being administered and the degree of the host's preexisting immunity. In this review, we discuss the current state of knowledge regarding the mechanisms of protection elicited by LAIV in children, contrast this with immune protection that develops upon vaccination with inactivated influenza vaccines, and briefly discuss both the potential advantages as well as challenges offered by this vaccination platform.

The human antibody response to influenza A virus infection and vaccination

The adaptive immune response to influenza virus infection is multifaceted and complex, involving antibody and cellular responses at both systemic and mucosal levels. Immune responses to natural infection with influenza virus in humans are relatively broad and long-lived, but influenza viruses can escape from these responses over time owing to their high mutation rates and antigenic flexibility. Vaccines are the best available countermeasure against infection, but vaccine effectiveness is low compared with other viral vaccines, and the induced immune response is narrow and short-lived. Furthermore, inactivated influenza virus vaccines focus on the induction of systemic IgG responses but do not effectively induce mucosal IgA responses. Here, I review the differences between natural infection and vaccination in terms of the antibody responses they induce and how these responses protect against future infection. A better understanding of how natural infection induces broad and long-lived immune responses will be key to developing next-generation influenza virus vaccines.

Use of traditional serological methods and oral fluids to assess immunogenicity in children aged 2-16 years after successive annual vaccinations with LAIV

Background

The UK introduced quadrivalent live attenuated influenza vaccine (qLAIV) for children in 2013/2014. The impact of annual vaccination on effectiveness and immunogenicity is being assessed.

Method

A phase III/IV open-label study of the immunogenicity of annual vaccination with qLAIV (Fluenz™) was conducted over three consecutive years (2014/15–2016/17) in 254, 249 and 162 children respectively. Serum responses to vaccine components were measured by Haemagglutination Inhibition (HAI) and anti-A(H1N1)pdm09 Neuraminidase (NAI) assays, stratified according to previous receipt of AS03_B-adjuvanted A(H1N1)pdm09 pandemic vaccine in 2009/10. Antibody levels to the A(H1N1)pdm09 and H3N2 vaccine components in oral fluids (OF) were explored using an ELISA.

Findings

More paired pre- and post-vaccination oral fluids (96%) than paired sera (87%) were obtained. Geometric mean titre rises using HAI assays were limited, with maximum rises seen in year one for both influenza B strains when 39% and 43% of subjects seroconverted (95% confidence interval 33–46% and 36–50%, respectively) and year two for influenza H3N2, when 40% (33–46%) individuals seroconverted. Prior pandemic vaccine receipt resulted in higher pre- and post-vaccination A(H1N1)pdm09 HAI titres and lower pre-and post-vaccination NAI (N1 neuraminidase) titres in all three years. OF results were congruent with HAI results; assay specificity compared to HAI was 88.1 and 71.6 percent, and sensitivity was 86.4 and 74.8 percent respectively for A(H1N1)pdm09 and H3N2.

Conclusion

In all three study years, vaccination with qLAIV resulted in poor antibody responses. However, OFs are an alternative specimen type that allows self sampling, can easily be obtained from children, and their analysis leads to similar conclusions as classic serology by HAI. Their suitability for seroprevalence studies should be investigated. We demonstrated a sustained effect from prior receipt of the AS03_B-adjuvanted A(H1N1)pdm09 vaccine, even after repeat vaccination with qLAIV indicating that early exposure to influenza antigens has a significant long lasting effect.

Differences in nasal immunoglobulin A responses to influenza vaccine strains after live attenuated influenza vaccine (LAIV) immunization in children

Different vaccine strains included in the live attenuated influenza vaccine (LAIV) have variable efficacy. The reasons for this are not clear and may include differences in immunogenicity. We report a Phase IV open-label study on the immunogenicity of a single dose of quadrivalent LAIV (Fluenz™ Tetra) in children during the 2015/16 season, to investigate the antibody responses to different strains. Eligible children were enrolled to receive LAIV; nasal samples were collected before and approximately 4 weeks after immunization. There was a significant increase in nasal immunoglobulin (Ig)A to the H3N2, B/Victoria lineage (B/Brisbane) and B/Yamagata lineage (B/Phuket) components, but not to the H1N1 component. The fold change in nasal IgA response was inversely proportional to the baseline nasal IgA titre for H1N1, H3N2 and B/Brisbane. We investigated possible associations that may explain baseline nasal IgA, including age and prior vaccination status, but found different patterns for different antigens, suggesting that the response is multi-factorial. Overall, we observed differences in immune responses to different viral strains included in the vaccine; the reasons for this require further investigation.

Efficacy, immunogenicity, and safety of an oral influenza vaccine: a placebo-controlled and active-controlled phase 2 human challenge study

BACKGROUND

Influenza is an important public health problem and existing vaccines are not completely protective. New vaccines that protect by alternative mechanisms are needed to improve efficacy of influenza vaccines. In 2015, we did a phase 1 trial of an oral influenza vaccine, VXA-A1.1. A favourable safety profile and robust immunogenicity results in that trial supported progression of the vaccine to the current phase 2 trial. The aim of this study was to evaluate efficacy of the vaccine in a human influenza challenge model.

METHODS

We did a single-site, placebo-controlled and active-controlled, phase 2 study at WCCT Global, Costa Mesa, CA, USA. Eligible individuals had an initial A/California/H1N1 haemagglutination inhibition titre of less than 20 and were aged 18-49 years and in good health. Individuals were randomly assigned (2:2:1) to receive a single immunisation of either 10¹¹ infectious units of VXA-A1.1 (a monovalent tablet vaccine) orally, a full human dose of quadrivalent inactivated influenza vaccine (IIV) via intramuscular injection, or matched placebo. Randomisation was done by computer-generated assignments with block size of five. An unmasked pharmacist provided the appropriate vaccines and placebos to the administrating nurse. Individuals receiving the treatments, investigators, and staff were all masked to group assignments. 90 days after immunisation, individuals without clinically significant symptoms or signs of influenza, an oral temperature of higher than 37·9°C, a positive result for respiratory viral shedding on a Biofire test, and any investigator-assessed contraindications were challenged intranasally with 0·5 mL wild-type A/CA/like(H1N1)pdm09 influenza virus. The primary outcomes were safety, which was assessed in all immunised participants through 365 days, and influenza-positive illness after viral challenge, which was assessed in individuals that received the viral challenge and the required number of assessments post viral challenge. This trial is registered with ClinicalTrials.gov, number NCT02918006.

RESULTS

Between Aug 31, 2016, and Jan 23, 2017, 374 individuals were assessed for eligibility, of whom 179 were randomly assigned to receive either VXA-A1.1 (n=71 [one individual did not provide a diary card, thus the solicited events were assessed in 70 individuals]), IIV (n=72), or placebo (n=36). Between Dec 2, 2016, and April 26, 2017, 143 eligible individuals (58 in the VXA-A1.1 group, 54 in the IIV group, and 31 in the placebo group) were challenged with influenza virus. VXA-A1.1 was well tolerated with no serious or medically significant adverse events. The most prevalent solicited adverse events for each of the treatment groups after immunisation were headache in the VXA-A1.1 (in five [7%] of 70 participants) and placebo (in seven [19%] of 36 participants) groups and tenderness at injection site in the IIV group (in 19 [26%] of 72 participants) Influenza-positive illness after challenge was detected in 17 (29%) of 58 individuals in the VXA-A1.1 group, 19 (35%) of 54 in the IIV group, and 15 (48%) of 31 in the placebo group.

INTERPRETATION

Orally administered VXA-A1.1 was well tolerated and generated protective immunity against virus shedding, similar to a licensed intramuscular IIV. These results represent a major step forward in developing a safe and effective oral influenza vaccine.

FUNDING

Department of Health and Human Services, Office of the Assistant Secretary for Preparedness and Response, and Biomedical Advanced Research and Development Authority.

The burden of severe cases of Influenza disease: the Friuli Venezia Giulia Region experience

Introduction

Influenza is a matter of serious concern for clinicians, in both outpatient and in-hospital settings. Worldwide, the 2017-18 epidemic proved to be the most severe since 2003-04. We report a real-world experience regarding the management of patients with influenza admitted to a large teaching hospital in the Friuli Venezia Giulia region during the 2017-2018 influenza season. We also provide a practical guide for the management of hospitalized influenza patients.

Methods

A retrospective observational analysis was conducted among all influenza patients requiring admission to our center during the 2017-18 season.

Results

Overall, 29 patients were admitted to the University Hospital of Udine during the 2017-18 season with a diagnosis of influenza. B virus was responsible for the majority of cases. More than 65.5% of the subjects presented with a complication. We estimated that 41.4% of the patients admitted were affected by a “severe form”. All these cases required admission to the Intensive Care Unit, with 27.6% and 10.3% needing Orotracheal Intubation and Extracorporeal Membrane Oxygenation, respectively. The fatality rate was 24.1%. Notably, only 9 subjects in our cohort had been vaccinated. Based on the experience acquired during the past season, we propose a practical guide to the management of influenza cases in everyday hospital practice.

Conclusion

The cornerstones of the management of all hospitalized influenza patients are the rapid identification and treatment of severe forms. Timely and strict adherence to contact and respiratory precautions are also fundamental to reducing the risk of intra-hospital outbreaks. Despite improvements in antiviral therapies and supportive measures, influenza-related morbidity and mortality remain high. In our opinion, a universal vaccination program is the only safe and effective method of filling the gap.

Effect of a Russian-backbone live-attenuated influenza vaccine with an updated pandemic H1N1 strain on shedding and immunogenicity among children in The Gambia: an open-label, observational, phase 4 study

BACKGROUND

The efficacy and effectiveness of the pandemic H1N1 (pH1N1) component in live attenuated influenza vaccine (LAIV) is poor. The reasons for this paucity are unclear but could be due to impaired replicative fitness of pH1N1 A/California/07/2009-like (Cal09) strains. We assessed whether an updated pH1N1 strain in the Russian-backbone trivalent LAIV resulted in greater shedding and immunogenicity compared with LAIV with Cal09.

METHODS

We did an open-label, prospective, observational, phase 4 study in Sukuta, a periurban area in The Gambia. We enrolled children aged 24-59 months who were clinically well. Children received one dose of the WHO prequalified Russian-backbone trivalent LAIV containing either A/17/California/2009/38 (Cal09) or A/17/New York/15/5364 (NY15) based on their year of enrolment. Primary outcomes were the percentage of children with LAIV strain shedding at day 2 and day 7, haemagglutinin inhibition seroconversion, and an increase in influenza haemagglutinin-specific IgA and T-cell responses at day 21 after LAIV. This study is nested within a randomised controlled trial investigating LAIV-microbiome interactions (NCT02972957).

FINDINGS

Between Feb 8, 2017, and April 12, 2017, 118 children were enrolled and received one dose of the Cal09 LAIV from 2016-17. Between Jan 15, 2018, and March 28, 2018, a separate cohort of 135 children were enrolled and received one dose of the NY15 LAIV from 2017-18, of whom 126 children completed the study. Cal09 showed impaired pH1N1 nasopharyngeal shedding (16 of 118 children [14%, 95% CI 8·0-21·1] with shedding at day 2 after administration of LAIV) compared with H3N2 (54 of 118 [46%, 36·6-55·2]; p<0·0001) and influenza B (95 of 118 [81%, 72·2-87·2]; p<0·0001), along with suboptimal serum antibody (seroconversion in six of 118 [5%, 1·9-10·7]) and T-cell responses (CD4+ interferon γ-positive and/or CD4+ interleukin 2-positive responses in 45 of 111 [41%, 31·3-50·3]). After the switch to NY15, a significant increase in pH1N1 shedding was seen (80 of 126 children [63%, 95% CI 54·4-71·9]; p<0·0001 compared with Cal09), along with improvements in seroconversion (24 of 126 [19%, 13·2-26·8]; p=0·011) and influenza-specific CD4+ T-cell responses (73 of 111 [66%, 60·0-75·6; p=0·00028]). The improvement in pH1N1 seroconversion with NY15 was even greater in children who were seronegative at baseline (24 of 64 children [38%, 95% CI 26·7-49·8] vs six of 79 children with Cal09 [8%, 2·8-15·8]; p<0·0001). Persistent shedding to day 7 was independently associated with both seroconversion (odds ratio 12·69, 95% CI 4·1-43·6; p<0·0001) and CD4+ T-cell responses (odds ratio 7·83, 95% CI 2·99-23·5; p<0·0001) by multivariable logistic regression.

INTERPRETATION

The pH1N1 component switch that took place between 2016 and 2018 might have overcome the poor efficacy and effectiveness reported with previous LAIV formulations. LAIV effectiveness against pH1N1 should, therefore, improve in upcoming influenza seasons. Our data highlight the importance of assessing replicative fitness, in addition to antigenicity, when selecting annual LAIV components.

FUNDING

The Wellcome Trust.

T and B Cell Immune Responses to Influenza Viruses in Pigs

Influenza viruses are an ongoing threat to humans and are endemic in pigs, causing considerable economic losses to farmers. Pigs are also a source of new viruses potentially capable of initiating human pandemics. Many tools including monoclonal antibodies, recombinant cytokines and chemokines, gene probes, tetramers, and inbred pigs allow refined analysis of immune responses against influenza. Recent advances in understanding of the pig innate system indicate that it shares many features with that of humans, although there is a larger gamma delta component. The fine specificity and mechanisms of cross-protective T cell immunity have yet to be fully defined, although it is clear that the local immune response is important. The repertoire of pig antibody response to influenza has not been thoroughly explored. Here we review current understanding of adaptive immune responses against influenza in pigs and the use of the pig as a model to study human disease.

Japanese Cedar Pollen-Specific IgA in Nasal Secretions and Nasal Allergy Symptoms

OBJECTIVE:

IgA-dependent degranulation of eosinophils and positive correlation between IgA and eosinophil cytotoxic protein levels in nasal secretions have been reported. However, the association between IgA and allergic reactions remains unclear. Therefore, we evaluated the changes in Japanese cedar-specific IgA levels and allergy symptoms after Japanese cedar pollen scattering in symptomatic and asymptomatic individuals sensitized to Japanese cedar pollen.

METHODS:

Nasal secretion and serum samples were collected from 31 participants (21 symptomatic and 10 asymptomatic participants) in January (preseason) and March (peak season). Japanese cedar-specific IgA or IgE levels were measured using ELISA with diamond-like carbon-coated chips.

RESULTS:

The ratio of Japanese cedar pollen-specific IgA to total IgA (rIgA) in the nasal secretions of symptomatic participants increased significantly in March compared with that in January ( P < .01); however, the ratio of specific IgE to total IgE (rIgE) in nasal secretions did not. rIgA in nasal secretions among asymptomatic participants also did not increase during pollen season. rIgA in nasal secretions was significantly correlated with nasal allergic symptoms (r = 0.82; P < .0001) with no significant correlation between rIgE and symptoms.

CONCLUSIONS:

To our knowledge, this is the first study to show an association between nasal symptoms and rIgA in nasal secretions, suggesting that rIgA is useful as an antigen-specific biomarker for allergic rhinitis or pollinosis. Furthermore, rIgA values in nasal secretions do not increase in asymptomatic participants sensitized to Japanese cedar during the pollen season.

Vaccine failure and serologic response to live attenuated and inactivated influenza vaccines in children during the 2013-2014 season

BACKGROUND

Recent observational studies in the United States indicated live attenuated influenza vaccine (LAIV) was less effective in children against clinical influenza infection caused by A(H1N1)pdm09 relative to inactivated influenza vaccine (IIV). During the 2013-2014 influenza season, we conducted an observational study among children aged 5-17 years to compare serologic responses to LAIV and IIV and explore factors associated with vaccine failure.

METHODS

One hundred and sixty-one children received one dose of trivalent IIV or quadrivalent LAIV according to parental preference. Baseline and postvaccination serum samples were tested with hemagglutination inhibition (HI) assays against vaccine reference strains. Geometric mean titers (GMT), geometric mean fold rise (GMFR), seroconversion, and seroprotection (HI titer ≥ 40) were used to assess response to vaccine. Active surveillance for acute respiratory illness was conducted during the influenza season and influenza cases were confirmed by reverse transcription polymerase chain reaction (RT-PCR). Logistic regression was used to examine the association between vaccine type and vaccine failure.

RESULTS

LAIV and IIV recipients were similar with respect to demographics and baseline GMT for each vaccine strain. RT-PCR confirmed influenza (vaccine failure) occurred in 8 (13%) of 62 LAIV recipients and 3 (3%) of 99 IIV recipients (p = .02). Postvaccination GMFR for A(H1N1)pdm09 was higher for IIV vs LAIV receipt (GMFR 3.3 vs. 0.8, p < .0001). Postvaccination titers against A(H1N1)pdm09 were ≥40 for 91% and 44% of IIV and LAIV recipients, respectively (p < .0001). Among 13 IIV and 18 LAIV recipients with seronegative baseline titer against A(H1N1pdm09), 54% and 0% seroconverted, respectively. LAIV receipt was the only factor associated with A(H1N1)pdm09 vaccine failure in the age-adjusted multivariable model (odds ratio 4.5, 95% CI 1.1-18.2).

CONCLUSION

Receipt of LAIV generated minimal HI antibody response in children, including among those seronegative at baseline. LAIV recipients had significant increased risk of A(H1N1)pdm09 infection compared to IIV recipients.

Intranasal inactivated influenza vaccines for the prevention of seasonal influenza epidemics

INTRODUCTION

Intranasal influenza vaccines are expected to confer protection among vaccine recipients by successful induction of mucosal immune response in the upper respiratory tract. Though only live attenuated influenza virus vaccines (LAIVs) are licensed and available for intranasal use in humans today, intranasal inactivated influenza vaccines (IIVs) are currently under reconsideration as a promising intranasal influenza vaccine.

AREAS COVERED

This review addresses the history of intranasal IIV research and development, along with a summary of the studies done so far to address the mechanism of action of intranasal IIVs.

EXPERT COMMENTARY

From numerous in vitro and in vivo studies, it has been shown that intranasal IIVs can protect hosts from a broad spectrum of influenza virus strains. In-depth studies of the mucosal antibody response following intranasal IIV administration have also elucidated the detailed functions of secretory IgA (immunoglobulin A) antibodies which are responsible for the mechanism of action of intranasal vaccines. Safe and effective intranasal IIVs are expected to be an important tool to combat seasonal influenza.

The Hurdles From Bench to Bedside in the Realization and Implementation of a Universal Influenza Vaccine

Influenza viruses circulate worldwide causing annual epidemics that have a substantial impact on public health. This is despite vaccines being in use for over 70 years and currently being administered to around 500 million people each year. Improvements in vaccine design are needed to increase the strength, breadth, and duration of immunity against diverse strains that circulate during regular epidemics, occasional pandemics, and from animal reservoirs. Universal vaccine strategies that target more conserved regions of the virus, such as the hemagglutinin (HA)-stalk, or recruit other cellular responses, such as T cells and NK cells, have the potential to provide broader immunity. Many pre-pandemic vaccines in clinical development do not utilize new vaccine platforms but use "tried and true" recombinant HA protein or inactivated virus strategies despite substantial leaps in fundamental research on universal vaccines. Significant hurdles exist for universal vaccine development from bench to bedside, so that promising preclinical data is not yet translating to human clinical trials. Few studies have assessed immune correlates derived from asymptomatic influenza virus infections, due to the scale of a study required to identity these cases. The realization and implementation of a universal influenza vaccine requires identification and standardization of set points of protective immune correlates, and consideration of dosage schedule to maximize vaccine uptake.

Clinical Expectations for Better Influenza Virus Vaccines-Perspectives from the Young Investigators' Point of View

The influenza virus is one of a few viruses that is capable of rendering an otherwise healthy person acutly bedridden for several days. This impressive knock-out effect, without prodromal symptoms, challenges our immune system. The influenza virus undergoes continuous mutations, escaping our pre-existing immunity and causing epidemics, and its segmented genome is subject to reassortment, resulting in novel viruses with pandemic potential. The personal and socieoeconomic burden from influenza is high. Vaccination is the most cost-effective countermeasure, with several vaccines that are available. The current limitations in vaccine effectivness, combined with the need for yearly updating of vaccine strains, is a driving force for research into developing new and improved influenza vaccines. The lack of public concern about influenza severity, and misleading information concerning vaccine safety contribute to low vaccination coverage even in high-risk groups. The success of future influeza vaccines will depend on an increased public awarness of the disease, and hence, the need for vaccination-aided through improved rapid diagnositics. The vaccines must be safe and broadly acting, with new, measurable correlates of protection and robust post-marketing safety studies, to improve the confidence in influenza vaccines.