Immune responses after live attenuated influenza vaccination

Vaccine Strategies Against RNA Viruses: Current Advances and Future Directions

The development of vaccines against RNA viruses has undergone a rapid evolution in recent years, particularly driven by the COVID-19 pandemic. This review examines the key roles that RNA viruses, with their high mutation rates and zoonotic potential, play in fostering vaccine innovation. We also discuss both traditional and modern vaccine platforms and the impact of new technologies, such as artificial intelligence, on optimizing immunization strategies. This review evaluates various vaccine platforms, ranging from traditional approaches (inactivated and live-attenuated vaccines) to modern technologies (subunit vaccines, viral and bacterial vectors, nucleic acid vaccines such as mRNA and DNA, and phage-like particle vaccines). To illustrate these platforms' practical applications, we present case studies of vaccines developed for RNA viruses such as SARS-CoV-2, influenza, Zika, and dengue. Additionally, we assess the role of artificial intelligence in predicting viral mutations and enhancing vaccine design. The case studies underscore the successful application of RNA-based vaccines, particularly in the fight against COVID-19, which has saved millions of lives. Current clinical trials for influenza, Zika, and dengue vaccines continue to show promise, highlighting the growing efficacy and adaptability of these platforms. Furthermore, artificial intelligence is driving improvements in vaccine candidate optimization and providing predictive models for viral evolution, enhancing our ability to respond to future outbreaks. Advances in vaccine technology, such as the success of mRNA vaccines against SARS-CoV-2, highlight the potential of nucleic acid platforms in combating RNA viruses. Ongoing trials for influenza, Zika, and dengue demonstrate platform adaptability, while artificial intelligence enhances vaccine design by predicting viral mutations. Integrating these innovations with the One Health approach, which unites human, animal, and environmental health, is essential for strengthening global preparedness against future RNA virus threats.

Safety, Immunogenicity and Protective Activity of a Modified Trivalent Live Attenuated Influenza Vaccine for Combined Protection Against Seasonal Influenza and COVID-19 in Golden Syrian Hamsters

BACKGROUND/OBJECTIVES

Influenza viruses and SARS-CoV-2 are currently cocirculating with similar seasonality, and both pathogens are characterized by a high mutational rate which results in reduced vaccine effectiveness and thus requires regular updating of vaccine compositions. Vaccine formulations combining seasonal influenza and SARS-CoV-2 strains can be considered promising and cost-effective tools for protection against both infections.

METHODS

We used a licensed seasonal trivalent live attenuated influenza vaccine (3×LAIV) as a basis for the development of a modified 3×LAIV/CoV-2 vaccine, where H1N1 and H3N2 LAIV strains encoded an immunogenic cassette enriched with conserved T-cell epitopes of SARS-CoV-2, whereas a B/Victoria lineage LAIV strain was unmodified. The trivalent LAIV/CoV-2 composition was compared to the classical 3×LAIV in the golden Syrian hamster model. Animals were intranasally immunized with the mixtures of the vaccine viruses, twice, with a 3-week interval. Immunogenicity was assessed on day 42 of the study, and the protective effect was established by infecting vaccinated hamsters with either influenza H1N1, H3N2 or B viruses or with SARS-CoV-2 strains of the Wuhan, Delta and Omicron lineages.

RESULTS

Both the classical 3×LAIV and 3×LAIV/CoV-2 vaccine compositions induced similar levels of serum antibodies specific to all three influenza strains, which resulted in comparable levels of protection against challenge from either influenza strain. Protection against SARS-CoV-2 challenge was more pronounced in the 3×LAIV/CoV-2-immunized hamsters compared to the classical 3×LAIV group. These data were accompanied by the higher magnitude of virus-specific cellular responses detected by ELISPOT in the modified trivalent LAIV group.

CONCLUSIONS

The modified trivalent live attenuated influenza vaccine encoding the T-cell epitopes of SARS-CoV-2 can be considered a promising tool for combined protection against seasonal influenza and COVID-19.

Head-to-head comparison of influenza vaccines in children: a systematic review and meta-analysis

Although vaccination is considered the most effective weapon against influenza, coverage rates, national vaccination policies, and funding vary largely around the globe. Despite their huge potential for achieving herd immunity, child-focused national vaccination strategies that favor pain-free nasal vaccines are uncommon. CENTRAL, Embase, and MEDLINE were last searched on November 13, 2023. Active-controlled randomized controlled trials comparing the live-attenuated intranasal vaccine with the inactivated intramuscular influenza vaccine in children were included. Event rates of laboratory-confirmed influenza virus infection, all-cause mortality, hospitalization, serious adverse events, adverse events, and financial outcomes were extracted based on the PRISMA 2020 Guideline. PROSPERO: CRD42021285412. Pooled odds ratios (ORs) with 95% confidence intervals (CI) were calculated using the random-effects model when at least three comparable outcomes were available. We found no significant difference between quadrivalent live-attenuated intranasal and trivalent inactivated intramuscular (OR = 1.48; 95% CI 0.49-4.45) or between trivalent live-attenuated intranasal and inactivated intramuscular vaccines (OR = 0.77, CI = 0.44-1.34) regarding their efficacy. However, the subgroup analysis of large, multi-center trials indicated that the trivalent live attenuated intranasal influenza vaccine was superior to the trivalent inactivated intramuscular influenza vaccine (12,154 people, OR = 0.50, CI = 0.28-0.88). Only 23 "vaccine-related serious adverse events" were recorded among 17 833 individuals, with no significant difference between methods. The widespread initiation of pediatric national flu vaccination programs prioritizing the live-attenuated intranasal influenza vaccine would be beneficial. Multi-continent, high-quality studies that include children younger than two years old and those living in subtropical and tropical regions are needed to further enhance our understanding.

Sequential immunization with chimeric hemagglutinin ΔNS1 attenuated influenza vaccines induces broad humoral and cellular immunity

Influenza viruses pose a threat to public health as evidenced by severe morbidity and mortality in humans on a yearly basis. Given the constant changes in the viral glycoproteins owing to antigenic drift, seasonal influenza vaccines need to be updated periodically and effectiveness often drops due to mismatches between vaccine and circulating strains. In addition, seasonal influenza vaccines are not protective against antigenically shifted influenza viruses with pandemic potential. Here, we have developed a highly immunogenic vaccination regimen based on live-attenuated influenza vaccines (LAIVs) comprised of an attenuated virus backbone lacking non-structural protein 1 (ΔNS1), the primary host interferon antagonist of influenza viruses, with chimeric hemagglutinins (cHA) composed of exotic avian head domains with a highly conserved stalk domain, to redirect the humoral response towards the HA stalk. In this study, we showed that cHA-LAIV vaccines induce robust serum and mucosal responses against group 1 stalk and confer antibody-dependent cell cytotoxicity activity. Mice that intranasally received cH8/1-ΔNS1 followed by a cH11/1-ΔNS1 heterologous booster had robust humoral responses for influenza A virus group 1 HAs and were protected from seasonal H1N1 influenza virus and heterologous highly pathogenic avian H5N1 lethal challenges. When compared with mice immunized with the standard of care or cold-adapted cHA-LAIV, cHA-ΔNS1 immunized mice had robust antigen-specific CD8+ T-cell responses which also correlated with markedly reduced lung pathology post-challenge. These observations support the development of a trivalent universal influenza vaccine for the protection against group 1 and group 2 influenza A viruses and influenza B viruses.

Deciphering immune responses: a comparative analysis of influenza vaccination platforms

Influenza still poses a significant challenge due to its high mutation rates and the low effectiveness of traditional vaccines. At present, antibodies that neutralize the highly variable hemagglutinin antigen are a major driver of the observed variable protection. To decipher how influenza vaccines can be improved, an analysis of licensed vaccine platforms was conducted, contrasting the strengths and limitations of their different mechanisms of protection. Through this review, it is evident that these vaccines do not elicit the robust cellular immune response critical for protecting high-risk groups. Emerging platforms, such as RNA vaccines, that induce robust cellular responses that may be additive to the recognized mechanism of protection through hemagglutinin inhibition may overcome these constraints to provide broader, protective immunity. By combining both humoral and cellular responses, such platforms could help guide the future influenza vaccine development.

Immunogenicity and protective efficacy of an inactivated infectious bronchitis virus vaccine candidate from a local isolate of Bangladesh

Objective

Infectious bronchitis (IB), a highly infectious acute viral disease, is a major burden to the chicken industry worldwide. The research aimed to develop an inactivated IB vaccine using local isolates and assess its immunogenicity compared to other commercial live IB vaccines.

Materials and Methods

An inactivated vaccine using a candidate IB virus (PP067159.1: Alim_IB_1001) of the QX genotype was developed according to WOAH guidelines. Chickens were vaccinated with three doses (0.25, 0.5, and 1.0 ml) at 7 days old, with a booster at 37 days old via subcutaneous (SC) and intramuscular (IM) routes. Blood samples were collected on days 7, 37, and 67 to measure immune response by indirect ELISA. On day 67, chickens were challenged with a virulent IBV strain to assess vaccine protection. The experimental IB vaccine's immunogenicity, protective efficacy, and antibody duration were compared to a live IB vaccine (Live CEVAC® IBird) using three vaccination schedules: killed-followed-killed, live-followed-killed, and live-followed-live.

Results

Chickens vaccinated with SC with 1.0 ml showed higher antibody titers compared to other SC and IM routes of vaccination. SC vaccination with 0.5 and 1 ml provided the highest protection (93%). The killed-followed-killed vaccination method produced a more consistent and protective level of antibody titers in chickens compared to the other vaccination schedules. The experimental inactivated IB vaccine led to a higher survival rate (93%) compared to live-followed-killed (87%) and live-followed-live (73%), with statistical significance (p < 0.01). All three chicken groups maintained protective antibody titers (>396) at 307 days, but titers declined faster in the live-followed-live and live-followed-killed groups compared to the killed-followed-killed group.

Conclusion

The study found that the experimental inactivated IB vaccination can protect commercial-layer chickens from natural IB outbreaks of the QX genotype.

Influenza Vaccine Effectiveness and Progress Towards a Universal Influenza Vaccine

At various times in recent decades, surges have occurred in optimism about the potential for universal influenza vaccines that provide strong, broad, and long-lasting protection and could substantially reduce the disease burden associated with seasonal influenza epidemics as well as the threat posed by pandemic influenza. Each year more than 500 million doses of seasonal influenza vaccine are administered around the world, with most doses being egg-grown inactivated subunit or split-virion vaccines. These vaccines tend to have moderate effectiveness against medically attended influenza for influenza A(H1N1) and influenza B, and somewhat lower for influenza A(H3N2) where differences between vaccine strains and circulating strains can occur more frequently due to antigenic drift and egg adaptations in the vaccine strains. Several enhanced influenza vaccine platforms have been developed including cell-grown antigen, the inclusion of adjuvants, or higher antigen doses, to improve immunogenicity and protection. During the COVID-19 pandemic there was unprecedented speed in development and roll-out of relatively new vaccine platforms, including mRNA vaccines and viral vector vaccines. These new platforms present opportunities to improve protection for influenza beyond existing products. Other approaches continue to be explored. Incremental improvements in influenza vaccine performance should be achievable in the short to medium term.

Evaluation of a novel intramuscular prime/intranasal boost vaccination strategy against influenza in the pig model

Live-attenuated influenza vaccines (LAIV) offer advantages over the commonly used inactivated split influenza vaccines. However, finding the optimal balance between sufficient attenuation and immunogenicity has remained a challenge. We recently developed an alternative LAIV based on the 2009 pandemic H1N1 virus with a truncated NS1 protein and lacking PA-X protein expression (NS1(1-126)-ΔPAX). This virus showed a blunted replication and elicited a strong innate immune response. In the present study, we evaluated the efficacy of this vaccine candidate in the porcine animal model as a pertinent in vivo system. Immunization of pigs via the nasal route with the novel NS1(1-126)-ΔPAX LAIV did not cause disease and elicited a strong mucosal immune response that completely blocked replication of the homologous challenge virus in the respiratory tract. However, we observed prolonged shedding of our vaccine candidate from the upper respiratory tract. To improve LAIV safety, we developed a novel prime/boost vaccination strategy combining primary intramuscular immunization with a haemagglutinin-encoding propagation-defective vesicular stomatitis virus (VSV) replicon, followed by a secondary immunization with the NS1(1-126)-ΔPAX LAIV via the nasal route. This two-step immunization procedure significantly reduced LAIV shedding, increased the production of specific serum IgG, neutralizing antibodies, and Th1 memory cells, and resulted in sterilizing immunity against homologous virus challenge. In conclusion, our novel intramuscular prime/intranasal boost regimen interferes with virus shedding and transmission, a feature that will help combat influenza epidemics and pandemics.

SARS-CoV-2 Vaccines: The Advantage of Mucosal Vaccine Delivery and Local Immunity

Immunity against respiratory pathogens is often short-term, and, consequently, there is an unmet need for the effective prevention of such infections. One such infectious disease is coronavirus disease 19 (COVID-19), which is caused by the novel Beta coronavirus SARS-CoV-2 that emerged around the end of 2019. The World Health Organization declared the illness a pandemic on 11 March 2020, and since then it has killed or sickened millions of people globally. The development of COVID-19 systemic vaccines, which impressively led to a significant reduction in disease severity, hospitalization, and mortality, contained the pandemic's expansion. However, these vaccines have not been able to stop the virus from spreading because of the restricted development of mucosal immunity. As a result, breakthrough infections have frequently occurred, and new strains of the virus have been emerging. Furthermore, SARS-CoV-2 will likely continue to circulate and, like the influenza virus, co-exist with humans. The upper respiratory tract and nasal cavity are the primary sites of SARS-CoV-2 infection and, thus, a mucosal/nasal vaccination to induce a mucosal response and stop the virus' transmission is warranted. In this review, we present the status of the systemic vaccines, both the approved mucosal vaccines and those under evaluation in clinical trials. Furthermore, we present our approach of a B-cell peptide-based vaccination applied by a prime-boost schedule to elicit both systemic and mucosal immunity.

Assessment of CD8+ T-cell mediated immunity in an influenza A(H3N2) human challenge model in Belgium: a single centre, randomised, double-blind phase 2 study

BACKGROUND

Protection afforded by inactivated influenza vaccines can theoretically be improved by inducing T-cell responses to conserved internal influenza A antigens. We assessed whether, in an influenza controlled human infection challenge, susceptible individuals receiving a vaccine boosting T-cell responses would exhibit lower viral load and decreased symptoms compared with placebo recipients.

METHODS

In this single centre, randomised, double-blind phase 2 study, healthy adult (aged 18-55 years) volunteers with microneutralisation titres of less than 20 to the influenza A(H3N2) challenge strain were enrolled at an SGS quarantine facility in Antwerp, Belgium. Participants were randomly assigned double-blind using a permuted-block list with a 3:2 allocation ratio to receive 0·5 mL intramuscular injections of modified vaccinia Ankara (MVA) expressing H3N2 nucleoprotein (NP) and matrix protein 1 (M1) at 1·5 × 108 plaque forming units (4·3 × 108 50% tissue culture infectious dose [TCID50]; MVA-NP+M1 group) or saline placebo (placebo group). At least 6 weeks later, participants were challenged intranasally with 0·5 mL of a 1 × 106 TCID50/mL dose of influenza A/Belgium/4217/2015 (H3N2). Nasal swabs were collected twice daily from day 2 until day 11 for viral PCR, and symptoms of influenza were recorded from day 2 until day 11. The primary outcome was to determine the efficacy of MVA-NP+M1 vaccine to reduce the degree of nasopharyngeal viral shedding as measured by the cumulative viral area under the curve using a log-transformed quantitative PCR. This study is registered with ClinicalTrials.gov, NCT03883113.

FINDINGS

Between May 2 and Oct 24, 2019, 145 volunteers were enrolled and randomly assigned to the MVA-NP+M1 group (n=87) or the placebo group (n=58). Of these, 118 volunteers entered the challenge period (71 in the MVA-NP+M1 group and 47 in the placebo group) and 117 participants completed the study (71 in the MVA-NP+M1 group and 46 in the placebo group). 78 (54%) of the 145 volunteers were female and 67 (46%) were male. The primary outcome, overall viral load as determined by quantitative PCR, did not show a statistically significant difference between the MVA-NP+M1 (mean 649·7 [95% CI 552·7-746·7) and placebo groups (mean 726·1 [604·0-848·2]; p=0·17). All reported treatment emergent adverse events (TEAEs; 11 in the vaccination phase and 51 in the challenge phase) were grade 1 and 2, except for two grade 3 TEAEs in the placebo group in the challenge phase. A grade 4 second trimester fetal death, considered possibly related to the MVA-NP+M1 vaccination, and an acute psychosis reported in a placebo participant during the challenge phase were reported.

INTERPRETATION

The use of an MVA vaccine to expand CD4+ or CD8+ T cells to conserved influenza A antigens in peripheral blood did not affect nasopharyngeal viral load in an influenza H3N2 challenge model in seronegative, healthy adults.

FUNDING

Department of Health and Human Services; Administration for Strategic Preparedness and Response; Biomedical Advanced Research and Development Authority; and Barinthus Biotherapeutics.

Intranasal influenza-vectored COVID-19 vaccines confer broad protection against SARS-CoV-2 XBB variants in hamsters

The XBB.1.5 subvariant has garnered significant attention due to its exceptional immune evasion and transmissibility. Significantly, the evolutionary trajectory of SARS-CoV-2 has shown continual progression, with a recent global shift observed from XBB to BA.2.86, exemplified by the emergence of the predominant JN.1 subvariant. This phenomenon highlights the need for vaccines that can provide broad-spectrum antigenic coverage. In this study, we utilized a NS1-deleted (dNS1) influenza viral vector to engineer an updated live-attenuated vectored vaccine called dNS1-XBB-RBD. This vaccine encodes the receptor-binding domain (RBD) protein of the XBB.1.5 strain. Our findings demonstrate that the dNS1-XBB-RBD vaccine elicits a similar systemic and mucosal immune response compared to its prototypic form, dNS1-RBD. In hamsters, the dNS1-XBB-RBD vaccine provided robust protection against the SARS-CoV-2 immune-evasive strains XBB.1.9.2.1 and Beta. Remarkably, nasal vaccination with dNS1-RBD, which encodes the ancestor RBD gene, also effectively protected hamsters against both the XBB.1.9.2.1 and Beta strains. These results provide valuable insights about nasal influenza-vectored vaccine and present a promising strategy for the development of a broad-spectrum vaccine against COVID-19 in the future.

Gonadal androgens are associated with decreased type I interferon production by plasmacytoid dendritic cells and increased IgG titres to BNT162b2 following co-vaccination with live attenuated influenza vaccine in adolescents

mRNA vaccine technologies introduced following the SARS-CoV-2 pandemic have highlighted the need to better understand the interaction of adjuvants and the early innate immune response. Type I interferon (IFN-I) is an integral part of this early innate response that primes several components of the adaptive immune response. Women are widely reported to respond better than men to tri- and quadrivalent influenza vaccines. Plasmacytoid dendritic cells (pDCs) are the primary cell type responsible for IFN-I production, and female pDCs produce more IFN-I than male pDCs since the upstream pattern recognition receptor Toll-like receptor 7 (TLR7) is encoded by X chromosome and is biallelically expressed by up to 30% of female immune cells. Additionally, the TLR7 promoter contains several putative androgen response elements, and androgens have been reported to suppress pDC IFN-I in vitro. Unexpectedly, therefore, we recently observed that male adolescents mount stronger antibody responses to the Pfizer BNT162b2 mRNA vaccine than female adolescents after controlling for natural SARS-CoV-2 infection. We here examined pDC behaviour in this same cohort to determine the impact of IFN-I on anti-spike and anti-receptor-binding domain IgG titres to BNT162b2. Through flow cytometry and least absolute shrinkage and selection operator (LASSO) modelling, we determined that serum-free testosterone was associated with reduced pDC IFN-I, but contrary to the well-described immunosuppressive role for androgens, the most bioactive androgen dihydrotestosterone was associated with increased IgG titres to BNT162b2. Also unexpectedly, we observed that co-vaccination with live attenuated influenza vaccine boosted the magnitude of IgG responses to BNT162b2. Together, these data support a model where systemic IFN-I increases vaccine-mediated immune responses, yet for vaccines with intracellular stages, modulation of the local IFN-I response may alter antigen longevity and consequently improve vaccine-driven immunity.

Early mucosal events promote distinct mucosal and systemic antibody responses to live attenuated influenza vaccine

Compared to intramuscular vaccines, nasally administered vaccines have the advantage of inducing local mucosal immune responses that may block infection and interrupt transmission of respiratory pathogens. Live attenuated influenza vaccine (LAIV) is effective in preventing influenza in children, but a correlate of protection for LAIV remains unclear. Studying young adult volunteers, we observe that LAIV induces distinct, compartmentalized, antibody responses in the mucosa and blood. Seeking immunologic correlates of these distinct antibody responses we find associations with mucosal IL-33 release in the first 8 hours post-inoculation and divergent CD8+ and circulating T follicular helper (cTfh) T cell responses 7 days post-inoculation. Mucosal antibodies are induced separately from blood antibodies, are associated with distinct immune responses early post-inoculation, and may provide a correlate of protection for mucosal vaccination. This study was registered as NCT04110366 and reports primary (mucosal antibody) and secondary (blood antibody, and nasal viral load and cytokine) endpoint data.

Leveraging human immune organoids for rational vaccine design

Current influenza A and B virus (IABV) vaccines provide suboptimal protection and efforts are underway to develop a universal IABV vaccine. Blood neutralizing antibodies are the current gold standard for protection, but many processes that regulate human IABV-specific immunity occur in mucosal and lymphoid tissues. We need an improved mechanistic understanding of how immune cells respond within these tissues to advance our current (slow and expensive) vaccine testing model. We posit that advanced in vitro models of human adaptive immunity can bridge some of the gaps between vaccine design, animal models, and human clinical trials. Here, we highlight how they can be integrated into current practices and play a role in reverse translating the defined features of protective vaccines to rationally design new candidates.

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.

Nucleoprotein as a Promising Antigen for Broadly Protective Influenza Vaccines

Annual vaccination is considered as the main preventive strategy against seasonal influenza. Due to the highly variable nature of major viral antigens, such as hemagglutinin (HA) and neuraminidase (NA), influenza vaccine strains should be regularly updated to antigenically match the circulating viruses. The influenza virus nucleoprotein (NP) is much more conserved than HA and NA, and thus seems to be a promising target for the design of improved influenza vaccines with broad cross-reactivity against antigenically diverse influenza viruses. Traditional subunit or recombinant protein influenza vaccines do not contain the NP antigen, whereas live-attenuated influenza vaccines (LAIVs) express the viral NP within infected cells, thus inducing strong NP-specific antibodies and T-cell responses. Many strategies have been explored to design broadly protective NP-based vaccines, mostly targeted at the T-cell mode of immunity. Although the NP is highly conserved, it still undergoes slow evolutionary changes due to selective immune pressure, meaning that the particular NP antigen selected for vaccine design may have a significant impact on the overall immunogenicity and efficacy of the vaccine candidate. In this review, we summarize existing data on the conservation of the influenza A viral nucleoprotein and review the results of preclinical and clinical trials of NP-targeting influenza vaccine prototypes, focusing on the ability of NP-specific immune responses to protect against diverse influenza viruses.

Chimeric hemagglutinin split vaccines elicit broadly cross-reactive antibodies and protection against group 2 influenza viruses in mice

Seasonal influenza virus vaccines are effective when they are well matched to circulating strains. Because of antigenic drift/change in the immunodominant hemagglutinin (HA) head domain, annual vaccine reformulations are necessary to maintain a match with circulating strains. In addition, seasonal vaccines provide little to no protection against newly emerging pandemic strains. Sequential vaccination with chimeric HA (cHA) constructs has been proven to direct the immune response toward the immunosubdominant but more conserved HA stalk domain. In this study, we show that immunization with group 2 cHA split vaccines in combination with the CpG 1018 adjuvant elicits broadly cross-reactive antibodies against all group 2 HAs, as well as systemic and local antigen-specific T cell responses. Antibodies elicited after sequential vaccination are directed to conserved regions of the HA such as the stalk and the trimer interface and also to the N2 neuraminidase (NA). Immunized mice were fully protected from challenge with a broad panel of influenza A viruses.

Considerations for vaccinating children against COVID-19

COVID-19 vaccines have been introduced in children and adolescents in many countries. However, high levels of community transmission and infection-derived immunity make the decision to introduce COVID-19 vaccination of children in countries yet to do so particularly challenging. For example, other vaccine preventable diseases, including measles and polio, generally have far higher childhood morbidity and mortality in low-income and middle-income countries (LMICs) than COVID-19, and coverage with these vaccines has declined during the pandemic. Many countries are yet to introduce pneumococcal conjugate and rotavirus vaccines for children, which prevent common causes of childhood death, or human papillomavirus vaccine for adolescents. The Pfizer and Moderna COVID-19 vaccines that have been widely tested in children and adolescents have a positive risk-benefit profile. However, the benefit is less compared with other life-saving vaccines in this age group, particularly in LMICs and settings with widespread infection-derived immunity. The resources required for rollout may also pose a considerable challenge in LMICs. In this paper, we describe COVID-19 in children, with a focus on LMICs, and summarise the published literature on safety, efficacy and effectiveness of COVID-19 vaccination in children and adolescents. We highlight the complexity of decision-making regarding COVID-19 vaccination of children now that most of this low-risk population benefit from infection-derived immunity. We emphasise that at-risk groups should be prioritised for COVID-19 vaccination; and that if COVID-19 vaccines are introduced for children, the opportunity should be taken to improve coverage of routine childhood vaccines and preventative healthcare. Additionally, we highlight the paucity of epidemiological data in LMICs, and that for future epidemics, measures need to be taken to ensure equitable access to safe and efficacious vaccines before exposure to infection.

A Randomized Controlled Trial to Compare Immunogenicity to Cell-Based Versus Live-Attenuated Influenza Vaccines in Children

BACKGROUND

Few studies have focused on the immune response to more recent influenza vaccine formulations such as cell-cultured inactivated influenza vaccine (ccIIV4) or live-attenuated influenza vaccine (LAIV4) in older children and young adults, or differences in immunoglobulin response using newer antibody landscape technology.

METHODS

Participants ages 4-21 were randomized to receive ccIIV4 (n = 112) or LAIV4 (n = 118). A novel high-throughput multiplex influenza antibody detection assay was used to provide detailed IgG, IgA, and IgM antibody isotypes, along with hemagglutination inhibition levels (HAI), measured pre- and 28 days post-vaccination.

RESULTS

The HAI and immunoglobulin isotype response to ccIIV4 was greater than LAIV4, with significant increases in IgG but not IgA or IgM. The youngest participants had the highest LAIV4 response. Prior LAIV4 vaccination was associated with a higher response to current season ccIIV4. Cross-reactive A/Delaware/55/2019(H1N1)pdm09 antibodies were present pre-vaccination and increased in response to ccIIV4, but not LAIV4. Immunoglobulin assays strongly correlated with and confirmed the findings of HAI titers to measure immune response.

CONCLUSIONS

Age and prior season vaccination may play a role in the immune response in children and young adults to ccIIV4 and LAIV4. While immunoglobulin isotypes provide high-level antigen-specific information, HAI titers alone can provide a meaningful representation of day 28 post-vaccination response.

CLINICAL TRIALS NO

NCT03982069.

Nasal shedding of vaccine viruses after immunization with a Russian-backbone live attenuated influenza vaccine in India

BACKGROUND

We present post-vaccination nasal shedding findings from the phase IV, community-based, triple-blinded RCT conducted to assess efficacy of trivalent LAIV and inactivated influenza vaccines in rural north India.

METHODS

Children aged 2-10 years received LAIV or intranasal placebo across 2015 and 2016, as per initial allocation. On days 2 and 4 post-vaccination, trained study nurses collected nasal swabs from randomly selected subset of trial participants based on operational feasibility, accounting for 10.0% and 11.4% of enrolled participants in 2015 and 2016, respectively. Swabs were collected in viral transport medium and transported under cold chain to laboratory for testing by reverse transcriptase real-time polymerase chain reaction.

RESULTS

In year 1, on day 2 post-vaccination, 71.2% (74/104) of LAIV recipients shed at least one of vaccine virus strains compared to 42.3% (44/104) on day 4. During year 1, on day 2 post-vaccination, LAIV-A(H1N1)pdm09 was detected in nasal swabs of 12% LAIV recipients, LAIV-A(H3N2) in 41%, and LAIV-B in 59%. In year 2, virus shedding was substantially lower; 29.6% (32/108) of LAIV recipients shed one of the vaccine virus strains on day 2 compared to 21.3% on day 4 (23/108).

CONCLUSION

At day 2 post-vaccination in year 1, two-thirds of LAIV recipients were shedding vaccine viruses. Shedding of vaccine viruses varied between strains and was lower in year 2. More research is needed to determine the reason for lower virus shedding and vaccine efficacy for LAIV-A(H1N1)pdm09.

Mucosal vaccines for SARS-CoV-2: triumph of hope over experience

Currently approved COVID-19 vaccines administered parenterally induce robust systemic humoral and cellular responses. While highly effective against severe disease, there is reduced effectiveness of these vaccines in preventing breakthrough infection and/or onward transmission, likely due to poor immunity elicited at the respiratory mucosa. As such, there has been considerable interest in developing novel mucosal vaccines that engenders more localised immune responses to provide better protection and recall responses at the site of virus entry, in contrast to traditional vaccine approaches that focus on systemic immunity. In this review, we explore the adaptive components of mucosal immunity, evaluate epidemiological studies to dissect if mucosal immunity conferred by parenteral vaccination or respiratory infection drives differential efficacy against virus acquisition or transmission, discuss mucosal vaccines undergoing clinical trials and assess key challenges and prospects for mucosal vaccine development.

DEVELOPMENT OF REASSORTANT INFLUENZA VACCINES: CLASSICAL REASSORTMENT OR REVERSE GENETICS?

An important feature of influenza vaccines, which distinguishes them from other immunobiological preparations, is that they have no fixed composition. Due to the constant influenza virus antigenic variability, production facilities require timely supply with relevant vaccine strains undoable due to the lack of proper method for the convenient, rapid and uninterrupted development of vaccine strains. Among the licensed influenza vaccines, classical inactivated and live influenza vaccines hold a special place. They are based on reassortant vaccine strains obtained by crossing currently circulating influenza virus with the so-called donor strain (cold-adapted attenuation donor for live influenza vaccines or high yield donor for inactivated vaccines). Vaccine strains for licensed live attenuated influenza vaccines are reassortants with the so-called 6:2 genome formula two genes encoding hemagglutinin and neuraminidase (HA and NA) belong to the current epidemic virus, and six genes encoding internal proteins (PB2, PB1, PA, NP, M and NS) to cold-adapted master donor virus. There is a very limited number of donors of attenuation. In Russia, there are cold-adapted viruses A/Leningrad/134/17/57 (H2N2) and B/USSR/60/69; in the USA (MedImmune) there are viruses A/Ann Arbor/6/60ca (H2N2) and B/Ann Arbor/1/66ca. MedImmune produces vaccine strains using reverse genetics technique. For other countries, this approach for obtaining vaccines is limited due to the need to purchase a license from the patent holders. In Russia, genetic manipulations with strains for the seasonal live influenza vaccine are not yet allowed; reassortants for the Russian live influenza vaccine are created only by classical reassortment in embryonated chicken eggs. Vaccine candidates for the inactivated influenza vaccine are prepared by the classical reassortment method, the requirements for them are more flexible and allow to use diverse genes combinations from wild type virus and master donor virus. High-yielding viruses such as A/PR/8/34 (H1N1), A/Texas/1/77 (H3N2), B/Lee/40 and some others are used as donors of internal genes. Unfortunately, the classical reassortment method does not always allow to promptly obtain a reassortant virus with a 6:2 genome formula. This is hindered by a number of reasons, ranging from the unique properties of a certain epidemic virus ending up with the constellation of genes. The reverse genetics method based on plasmids is an alternative approach to create reassortant vaccine strains allowing to reliably and quickly obtain reassortant viruses of a set 6:2 genome formula. However, this method also has certain weaknesses. This review discusses the advantages and disadvantages of development of conventional influenza vaccine candidates by reverse genetics and classical reassortment in developing chick embryos.

Mucosal and systemic neutralizing antibodies to norovirus induced in infant mice orally inoculated with recombinant rotaviruses

Rotaviruses (RVs) preferentially replicate in the small intestine and frequently cause severe diarrheal disease, and the following enteric infection generally induces variable levels of protective systemic and mucosal immune responses in humans and other animals. Rhesus rotavirus (RRV) is a simian RV that was previously used as a human RV vaccine and has been extensively studied in mice. Although RRV replicates poorly in the suckling mouse intestine, infection induces a robust and protective antibody response. The recent availability of plasmid only-based RV reverse genetics systems has enabled the generation of recombinant RVs expressing foreign proteins. However, recombinant RVs have not yet been experimentally tested as potential vaccine vectors to immunize against other gastrointestinal pathogens in vivo. This is a newly available opportunity because several live-attenuated RV vaccines are already widely administered to infants and young children worldwide. To explore the feasibility of using RV as a dual vaccine vector, we rescued replication-competent recombinant RRVs harboring bicistronic gene segment 7 that encodes the native RV nonstructural protein 3 (NSP3) protein and a human norovirus (HuNoV) VP1 protein or P domain from the predominant genotype GII.4. The rescued viruses expressed HuNoV VP1 or P protein in infected cells in vitro and elicited systemic and local antibody responses to HuNoV and RRV following oral infection of suckling mice. Serum IgG and fecal IgA from infected suckling mice bound to and neutralized both RRV and HuNoV. These findings have encouraging practical implications for the design of RV-based next-generation multivalent enteric vaccines to target HuNoV and other human enteric pathogens.

Revisiting live attenuated influenza vaccine efficacy among children in developing countries

Seasonal influenza epidemics cause significant pediatric mortality and morbidity worldwide. Live attenuated influenza vaccines (LAIVs) can be administered intranasally, induce a broad and robust immune response, demonstrate higher yields during manufacturing as compared to inactivated influenza vaccines (IIVs), and thereby represent an attractive possibility for young children in developing countries. We summarize recent pediatric studies evaluating LAIV efficacy in developing countries where a large proportion of the influenza-virus-associated respiratory disease burden occurs. Recently, two randomized controlled trials (RCTs) assessing Russian-backbone trivalent LAIV in children reported contradictory results; vaccine efficacy varied between Bangladesh (41 %) and Senegal (0.0 %) against all influenza viral strains. Prior to 2013, Ann Arbor-based LAIV demonstrated superior efficacy as compared to IIV. However, due to low effectiveness of the Ann Arbor-based LAIV against influenza A(H1N1)pdm09-like viruses, the CDC Advisory Committee on Immunization Practices (ACIP) recommended against the use of LAIV during the 2016-17 and 2017-18 influenza seasons. Reduced replicative fitness of the A(H1N1)pdm09 LAIV strains is thought to have led to the low effectiveness of the Ann-Arbor-based LAIV. Once the A(H1N1)pdm09 component was updated, the ACIP reintroduced the Ann-Arbor-based LAIV as a vaccine choice for the 2018-19 influenza season. In 2021, results from a 2-year RCT evaluating the Russian-backbone trivalent LAIV in rural north India reported that LAIV demonstrated significantly lower efficacy compared to IIV, but in Year 2, the vaccine efficacy for LAIV and IIV was comparable. A profounder understanding of the mechanisms underlying varied efficacy of LAIV in developing countries is warranted. Assessing replicative fitness, in addition to antigenicity, when selecting annual A(H1N1)pdm09 components in the Russian-backbone trivalent LAIVs is essential and may ultimately, enable widespread utility in resource-poor settings.

Post-vaccination serum cytokines levels correlate with breakthrough influenza infections

Post-vaccination cytokine levels from 256 young adults who subsequently suffered breakthrough influenza infections were compared with matched controls. Modulation within the immune system is important for eliciting a protective response, and the optimal response differs according to vaccine formulation and delivery. For both inactivated influenza vaccine (IIV) and live attenuated influenza vaccines (LAIV) lower levels of IL-8 were observed in post-vaccination sera. Post-vaccination antibody levels were higher and IFN-γ levels were lower in IIV sera compared to LAIV sera. Subjects who suffered breakthrough infections after IIV vaccination had higher levels of sCD25 compared to the control group. There were differences in LAIV post-vaccination interleukin levels for subjects who subsequently suffered breakthrough infections, but these differences were masked in subjects who received concomitant vaccines. Wide variances, sex-based differences and confounders such as concomitant vaccines thwart the establishment of specific cytokine responses as a correlate of protection, but our results provide real world evidence that the status of the immune system following vaccination is important for successful vaccination and subsequent protection against disease.

Understanding immunity to influenza: implications for future vaccine development

INTRODUCTION

Influenza virus changes its genotype through antigenic drift or shift making it difficult to develop immunity to infection or vaccination. Zoonotic influenza A virus (IAV) strains can become established in humans. Several impediments to human infection and transmission include sialic acid expression, host anti-viral factors (including interferons), and other elements that govern viral replication. Controlling influenza infection, replication, and transmission is important because IAVs cause annual epidemics and occasional pandemics. Effective seasonal influenza vaccines exist, but these vaccines do not fully protect against novel or pandemic strains.

AREAS COVERED

With new vaccine production technology, vaccines can be produced rapidly. Universal IAV vaccines are being developed to protect against seasonal, novel, and zoonotic IAVs. These efforts are being enhanced and accelerated by a better understanding the host immune response to influenza viruses.

EXPERT OPINION

This review discusses several implications for future influenza vaccine development. Host immune responses to influenza virus infection or vaccination can guide vaccine development as anti-influenza immunity is affected by responses influenced by the previous immune history including first and subsequent exposures to influenza virus infections and vaccinations.

Strain development of A/H1N1pdm09 candidate vaccine viruses for the 2021–22 northern hemisphere influenza season

The vaccine effectiveness (VE) of the A/H1N1pdm09 component of the 2017–18 quadrivalent live attenuated influenza vaccine (QLAIV) was improved by performing rational haemagglutinin (HA) mutagenesis. Introducing N125D, D127E, D222G and R223Q substitutions into the HA protein of A/Slovenia/2903/2015 (A/SLOV15) enhanced replicative fitness in primary human nasal epithelial cells (hNECs). This allowed A/SLOV15 to overcome inter-strain competition in QLAIV, resulting in improved VE.

During strain development for the 2021–22 QLAIV formulation, A/H1N1pdm09 LAIV viruses containing wild-type (WT) HA and neuraminidase (NA) sequences were found to replicate poorly in embryonated eggs and hNECs. We aimed to enhance replicative fitness via the HA mutagenesis approach that was performed previously for A/SLOV15. Therefore, combinations of these four mutations were introduced into the HA protein of representative 6B.1A-5a.2 viruses, A/Victoria/2570/2019 and A/Victoria/1/2020 (A/VIC1). Replicative fitness of A/VIC1 V7 was improved ~30-fold in eggs and ~300-fold in hNECs relative to its parent, without compromising other critical LAIV characteristics.

Intranasal M2SR (M2-Deficient Single Replication) H3N2 Influenza Vaccine Provides Enhanced Mucosal and Serum Antibodies in Adults

BACKGROUND

We previously demonstrated that an intranasal dose of 108 50% tissue culture infectious dose (TCID50) M2-deficient single replication (M2SR) influenza vaccine protected against highly drifted H3N2 influenza challenge in a subset of subjects who demonstrated ≥2-fold increase in microneutralization (MN) antibodies to Belgium2015 (the challenge strain) after vaccination. Here, we describe a phase 1b, observer-blinded, dose-escalation study demonstrating an increased proportion of responders with this signal of immune protection.

METHODS

Serosusceptible subjects aged 18-49 years were randomized to receive 2 doses (108-109 TCID50) of M2SR or placebo administered 28 days apart. Clinical specimens were collected before and after each dose. The primary objective was to demonstrate safety of M2SR vaccines.

RESULTS

The vaccine was well tolerated at all dose levels. Against Belgium2015, ≥ 2-fold increases in MN antibodies were noted among 40% (95% confidence interval [CI], 24.9%-56.7%) of subjects following a single 108 TCID50 M2SR dose and among 80.6% (95% CI, 61.4%-92.3%) after 109 dose (P < .001). A single 109 TCID50 dose of M2SR generated ≥4-fold hemagglutination inhibition antibody seroconversion against the vaccine strain in 71% (95% CI, 52.0%-85.8%) of recipients. Mucosal and cellular immune responses were also induced.

CONCLUSIONS

These results indicate that M2SR may provide substantial protection against infection with highly drifted strains of H3N2 influenza.

CLINICAL TRIALS REGISTRATION

NCT03999554.

Exploring Prime-Boost Vaccination Regimens with Different H1N1 Swine Influenza A Virus Strains and Vaccine Platforms

In a previous vaccination study in pigs, heterologous prime-boost vaccination with whole-inactivated H1N1 virus vaccines (WIV) induced superior antibody responses and protection compared to homologous prime-boost vaccination. However, no pan-H1 antibody response was induced. Therefore, to stimulate both local and systemic immune responses, we first vaccinated pigs intranasally with a pseudorabies vector vaccine expressing the pH1N1 hemagglutinin (prvCA09) followed by a homologous or heterologous WIV booster vaccine. Homologous and heterologous WIV-WIV vaccinated groups and mock-vaccinated or prvCA09 single-vaccinated pigs served as control groups. Five weeks after the second vaccination, pigs were challenged with a homologous pH1N1 or one of two heterologous H1N2 swine influenza A virus strains. A single prvCA09 vaccination resulted in complete protection against homologous challenge, and vector-WIV vaccinated groups were significantly better protected against heterologous challenge compared to the challenge control group or WIV-WIV vaccinated groups. Furthermore, vector-WIV vaccination resulted in broader hemagglutination inhibition antibody responses compared to WIV-WIV vaccination and higher numbers of antibody-secreting cells in peripheral blood, draining lymph nodes and nasal mucosa. However, even though vector-WIV vaccination induced stronger antibody responses and protection, we still failed to induce a pan-H1 antibody response.

Optimizing the Live Attenuated Influenza A Vaccine Backbone for High-Risk Patient Groups

Together with inactivated influenza vaccines (IIV), live attenuated influenza vaccines (LAIV) are an important tool to prevent influenza A virus (IAV) illnesses in patients. LAIVs present the advantages to have a needle-free administration and to trigger a mucosal immune response. LAIV is approved for healthy 2- to 49-year old individuals. However, due to its replicative nature and higher rate of adverse events at-risk populations are excluded from the benefits of this vaccine. Using targeted mutagenesis, we modified the nonstructural protein 1 of the currently licensed LAIV in order to impair its ability to bind the host cellular protein CPSF30 and thus its ability to inhibit host mRNA poly-adenylation. We characterized our optimized LAIV (optiLAIV) in three different mouse models mimicking healthy and high-risk patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against homosubtypic and hetesubtypic influenza strain challenges. We confirmed the safer profile of optiLAIV in Stat1^-/- mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate observed following LAIV inoculation. Using a human nasal 3D tissue model, we showed an increased induction of ER stress-related genes following immunization with optiLAIV. Induction of ER stress was previously shown to improve antigen-specific immune responses and is proposed as the mechanism of action of the licensed adjuvant AS03. This study characterizes a safer LAIV candidate in two mouse models mimicking infants and severely immunocompromised patients and proposes a simple attenuation strategy that could broaden LAIV application and reduce influenza burden in high-risk populations. IMPORTANCE Live attenuated influenza vaccine (LAIV) is a needle-free, mucosal vaccine approved for healthy 2- to 49-year old individuals. Its replicative nature and higher rate of adverse events excludes at-risk populations. We propose a strategy to improve LAIV safety and explore the possibility to expand its applications in children under 2-year old and immunocompromised patients. Using a neonatal mouse model, we show faster clearance of our optimized vaccine (optiLAIV) compared to the licensed LAIV. Despite lower replication, optiLAIV equally protected mice against influenza virus challenges. We confirmed the safer profile of optiLAIV in Stat1^-/- mice (highly susceptible to viral infections) by showing no signs of morbidity compared to a 50% mortality rate from LAIV. OptiLAIV could expand the applications of the current LAIV and help mitigate the burden of IAV in susceptible populations.

Frontline workers: Mediators of mucosal immunity in community acquired pneumonia and COVID-19

The current COVID-19 pandemic has highlighted a need to further understand lung mucosal immunity to reduce the burden of community acquired pneumonia, including that caused by the SARS-CoV-2 virus. Local mucosal immunity provides the first line of defence against respiratory pathogens, however very little is known about the mechanisms involved, with a majority of literature on respiratory infections based on the examination of peripheral blood. The mortality for severe community acquired pneumonia has been rising annually, even prior to the current pandemic, highlighting a significant need to increase knowledge, understanding and research in this field. In this review we profile key mediators of lung mucosal immunity, the dysfunction that occurs in the diseased lung microenvironment including the imbalance of inflammatory mediators and dysbiosis of the local microbiome. A greater understanding of lung tissue-based immunity may lead to improved diagnostic and prognostic procedures and novel treatment strategies aimed at reducing the disease burden of community acquired pneumonia, avoiding the systemic manifestations of infection and excess morbidity and mortality.

Intranasal administration of a single dose of MVA-based vaccine candidates against COVID-19 induced local and systemic immune responses and protects mice from a lethal SARS-CoV-2 infection

Current coronavirus disease-19 (COVID-19) vaccines are administered by the intramuscular route, but this vaccine administration failed to prevent severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus infection in the upper respiratory tract, mainly due to the absence of virus-specific mucosal immune responses. It is hypothesized that intranasal (IN) vaccination could induce both mucosal and systemic immune responses that blocked SARS-CoV-2 transmission and COVID-19 progression. Here, we evaluated in mice IN administration of three modified vaccinia virus Ankara (MVA)-based vaccine candidates expressing the SARS-CoV-2 spike (S) protein, either the full-length native S or a prefusion-stabilized [S(3P)] protein; SARS-CoV-2-specific immune responses and efficacy were determined after a single IN vaccine application. Results showed that in C57BL/6 mice, MVA-based vaccine candidates elicited S-specific IgG and IgA antibodies in serum and bronchoalveolar lavages, respectively, and neutralizing antibodies against parental and SARS-CoV-2 variants of concern (VoC), with MVA-S(3P) being the most immunogenic vaccine candidate. IN vaccine administration also induced polyfunctional S-specific Th1-skewed CD4+ and cytotoxic CD8+ T-cell immune responses locally (in lungs and bronchoalveolar lymph nodes) or systemically (in spleen). Remarkably, a single IN vaccine dose protected susceptible K18-hACE2 transgenic mice from morbidity and mortality caused by SARS-CoV-2 infection, with MVA-S(3P) being the most effective candidate. Infectious SARS-CoV-2 viruses were undetectable in lungs and nasal washes, correlating with high titers of S-specific IgGs and neutralizing antibodies against parental SARS-CoV-2 and several VoC. Moreover, low histopathological lung lesions and low levels of pro-inflammatory cytokines in lungs and nasal washes were detected in vaccinated animals. These results demonstrated that a single IN inoculation of our MVA-based vaccine candidates induced potent immune responses, either locally or systemically, and protected animal models from COVID-19. These results also identified an effective vaccine administration route to induce mucosal immunity that should prevent SARS-CoV-2 host-to-host transmission.

The role of cell-mediated immunity against influenza and its implications for vaccine evaluation

Influenza vaccines remain the most effective tools to prevent flu and its complications. Trivalent or quadrivalent inactivated influenza vaccines primarily elicit antibodies towards haemagglutinin and neuraminidase. These vaccines fail to induce high protective efficacy, in particular in older adults and immunocompromised individuals and require annual updates to keep up with evolving influenza strains (antigenic drift). Vaccine efficacy declines when there is a mismatch between its content and circulating strains. Current correlates of protection are merely based on serological parameters determined by haemagglutination inhibition or single radial haemolysis assays. However, there is ample evidence showing that these serological correlates of protection can both over- or underestimate the protective efficacy of influenza vaccines. Next-generation universal influenza vaccines that induce cross-reactive cellular immune responses (CD4+ and/or CD8+ T-cell responses) against conserved epitopes may overcome some of the shortcomings of the current inactivated vaccines by eliciting broader protection that lasts for several influenza seasons and potentially enhances pandemic preparedness. Assessment of cellular immune responses in clinical trials that evaluate the immunogenicity of these new generation vaccines is thus of utmost importance. Moreover, studies are needed to examine whether these cross-reactive cellular immune responses can be considered as new or complementary correlates of protection in the evaluation of traditional and next-generation influenza vaccines. An overview of the assays that can be applied to measure cell-mediated immune responses to influenza with their strengths and weaknesses is provided here.

Intranasal administration of a virus like particles-based vaccine induces neutralizing antibodies against SARS-CoV-2 and variants of concern

BACKGROUND

The highly contagious SARS-CoV-2 is mainly transmitted by respiratory droplets and aerosols. Consequently, people are required to wear masks and maintain a social distance to avoid spreading of the virus. Despite the success of the commercially available vaccines, the virus is still uncontained globally. Given the tropism of SARS-CoV-2, a mucosal immune reaction would help to reduce viral shedding and transmission locally. Only seven out of hundreds of ongoing clinical trials are testing the intranasal delivery of a vaccine against COVID-19.

METHODS

In the current study, we evaluated the immunogenicity of a traditional vaccine platform based on virus-like particles (VLPs) displaying RBD of SARS-CoV-2 for intranasal administration in a murine model. The candidate vaccine platform, CuMVTT -RBD, has been optimized to incorporate a universal T helper cell epitope derived from tetanus-toxin and is self-adjuvanted with TLR7/8 ligands.

RESULTS

CuMVTT -RBD vaccine elicited a strong systemic RBD- and spike-IgG and IgA antibodies of high avidity. Local immune response was assessed, and our results demonstrate a strong mucosal antibody and plasma cell production in lung tissue. Furthermore, the induced systemic antibodies could efficiently recognize and neutralize different variants of concern (VOCs).

CONCLUSION

Our data demonstrate that intranasal administration of CuMVTT -RBD induces a protective systemic and local specific antibody response against SARS-CoV-2 and its VOCs.

Current Opinion in LAIV: A Matter of Parent Virus Choice

Influenza is still a frequent seasonal infection of the upper respiratory tract, which may have deadly consequences, especially for the elderly. This is in spite of the availability of vaccines suggested for persons above 65 years of age. Two types of conventional influenza vaccines are currently licensed for use-live attenuated and inactivated vaccines. Depending on local regulatory requirements, live attenuated vaccines are produced by the reverse genetics technique or by classical reassortment in embryonated chicken eggs. Sometimes, the efficiency of classical reassortment is complicated by certain properties of the wild-type parent virus. Cases of low efficacy of vaccines have been noted, which, among other reasons, may be associated with suboptimal properties of the wild-type parent virus that are not considered when recommendations for influenza vaccine composition are made. Unfortunately, knowledge surrounding the roles of properties of the circulating influenza virus and its impact on the efficacy of the reassortment process, vaccination efficiency, the infectivity of the vaccine candidates, etc., is now scattered in different publications. This review summarizes the main features of the influenza virus that may dramatically affect different aspects of the preparation of egg-derived live attenuated vaccine candidates and their effectiveness. The author expresses her personal view, which may not coincide with the opinion of other experts in the field of influenza vaccines.

Intranasal inoculation of an MVA-based vaccine induces IgA and protects the respiratory tract of hACE2 mice from SARS-CoV-2 infection

Despite the ability of current vaccines to significantly prevent severe disease due to Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), vaccinated individuals are still susceptible to infection and contribute to the spread of the virus. The present study demonstrates that a live, replication-deficient recombinant virus vaccine induces greater immunity and a greater level of protection in the respiratory tract of susceptible transgenic mice when inoculated intranasally compared with intramuscularly. Second-generation vaccines administered via the upper respiratory tract have the potential to limit the spread of SARS-CoV-2 more effectively than current vaccines.

Current vaccines have greatly diminished the severity of the COVID-19 pandemic, even though they do not entirely prevent infection and transmission, likely due to insufficient immunity in the upper respiratory tract. Here, we compare intramuscular and intranasal administration of a live, replication-deficient modified vaccinia virus Ankara (MVA)–based Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) spike (S) vaccine to raise protective immune responses in the K18-hACE2 mouse model. Using a recombinant MVA expressing firefly luciferase for tracking, live imaging revealed luminescence of the respiratory tract of mice within 6 h and persisting for 3 d following intranasal inoculation, whereas luminescence remained at the site of intramuscular vaccination. Intramuscular vaccination induced S-binding–Immunoglobulin G (IgG) and neutralizing antibodies in the lungs, whereas intranasal vaccination also induced Immunoglobulin A (IgA) and higher levels of antigen-specific CD3⁺CD8⁺IFN-γ⁺ T cells. Similarly, IgG and neutralizing antibodies were present in the blood of mice immunized intranasally and intramuscularly, but IgA was detected only after intranasal inoculation. Intranasal boosting increased IgA after intranasal or intramuscular priming. While intramuscular vaccination prevented morbidity and cleared SARS-CoV-2 from the respiratory tract within several days after challenge, intranasal vaccination was more effective as neither infectious virus nor viral messenger (m)RNAs were detected in the nasal turbinates or lungs as early as 2 d after challenge, indicating prevention or rapid elimination of SARS-CoV-2 infection. Additionally, we determined that neutralizing antibody persisted for more than 6 mo and that serum induced to the Wuhan S protein neutralized pseudoviruses expressing the S proteins of variants, although with less potency, particularly for Beta and Omicron.

Adenoviral-Vectored Centralized Consensus Hemagglutinin Vaccine Provides Broad Protection against H2 Influenza a Virus

Several influenza pandemics have occurred in the past century, one of which emerged in 1957 from a zoonotic transmission of H2N2 from an avian reservoir into humans. This pandemic caused 2–4 million deaths and circulated until 1968. Since the disappearance of H2N2 from human populations, there has been waning immunity against H2, and this subtype is not currently incorporated into seasonal vaccines. However, H2 influenza remains a pandemic threat due to consistent circulation in avian reservoirs. Here, we describe a method of pandemic preparedness by creating an adenoviral-vectored centralized consensus vaccine design against human H2 influenza. We also assessed the utility of serotype-switching to enhance the protective immune responses seen with homologous prime-boosting strategies. Immunization with an H2 centralized consensus showed a wide breadth of antibody responses after vaccination, protection against challenge with a divergent human H2 strain, and significantly reduced viral load in the lungs after challenge. Further, serotype switching between two species C adenoviruses enhanced protective antibody titers after heterologous boosting. These data support the notion that an adenoviral-vectored H2 centralized consensus vaccine has the ability to provide broadly cross-reactive immune responses to protect against divergent strains of H2 influenza and prepare for a possible pandemic.

Haemagglutinin substitutions N125D, D127E, D222G and R223Q improve replicative fitness and vaccine effectiveness of an A/H1N1pdm09 live attenuated influenza vaccine virus by enhancing α-2,6 receptor binding

During 2013–14 and 2015–16, A/H1N1pdm09 live attenuated influenza vaccine (LAIV) viruses replicated inefficiently in primary human nasal epithelial cells (hNEC). This led to reduced vaccine effectiveness (VE) in quadrivalent formulations, mediated by inter-strain competition. By mutating the haemagglutinin (HA) protein, we aimed to enhance hNEC replication of a novel A/H1N1pdm09 vaccine strain to overcome competition and improve VE. Combinations of N125D, D127E, D222G and R223Q substitutions were introduced to the HA protein of A/Slovenia/2903/2015 (A/SLOV15). A/SLOV15 S13, containing all four HA substitutions, produced approximately 1000-fold more virus than parental V1 during hNEC infection. Immunogenicity in ferrets was increased by approximately 10-fold, without compromising yield in eggs or antigenic match to wild-type (wt) reference strains. Despite S13 and V1 being antigenically similar, only S13 protected ferrets from wt virus shedding and fever post-challenge. Crucially, these data suggested that enhanced fitness allowed S13 to overcome inter-strain competition in quadrivalent LAIV (QLAIV). This improved efficacy was later validated by real-world VE data. S13 displayed increased binding avidity to a mammalian-like α-2,6 receptor analogue (6-SLN), relative to V1, while maintaining avian-like 3-SLN avidity. In silico modelling of the HA receptor binding site revealed additional interactions in the S13:6-SLN binding network and a mild increase in 6-SLN binding energy, indicating a possible mechanism for increased α-2,6 receptor-binding avidity. These data confirm that rational HA mutagenesis can be used to optimise hNEC replication and VE for A/H1N1pdm09 LAIV viruses.

A live attenuated virus-based intranasal COVID-19 vaccine provides rapid, prolonged, and broad protection against SARS-CoV-2

Remarkable progress has been made in developing intramuscular vaccines against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); however, they are limited with respect to eliciting local immunity in the respiratory tract, which is the primary infection site for SARS-CoV-2. To overcome the limitations of intramuscular vaccines, we constructed a nasal vaccine candidate based on an influenza vector by inserting a gene encoding the receptor-binding domain (RBD) of the spike protein of SARS-CoV-2, named CA4-dNS1-nCoV-RBD (dNS1-RBD). A preclinical study showed that in hamsters challenged 1 d after single-dose vaccination or 9 months after booster vaccination, dNS1-RBD largely mitigated lung pathology, with no loss of body weight. Moreover, such cellular immunity is relatively unimpaired for the most concerning SARS-CoV-2 variants, especially for the latest Omicron variant. In addition, this vaccine also provides cross-protection against H1N1 and H5N1 influenza viruses. The protective immune mechanism of dNS1-RBD could be attributed to the innate immune response in the nasal epithelium, local RBD-specific T cell response in the lung, and RBD-specific IgA and IgG response. Thus, this study demonstrates that the intranasally delivered dNS1-RBD vaccine candidate may offer an important addition to the fight against the ongoing coronavirus disease 2019 pandemic and influenza infection, compensating limitations of current intramuscular vaccines.

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.

Dealing with a mucosal viral pandemic: lessons from COVID-19 vaccines

The development and deployment of vaccines against COVID-19 demonstrated major successes in providing immunity and preventing severe disease and death. Yet SARS-CoV-2 evolves and vaccine-induced protection wanes, meaning progress in vaccination strategies is of upmost importance. New vaccines directed at emerging viral strains are being developed while vaccination schemes with booster doses and combinations of different platform-based vaccines are being tested in trials and real-world settings. Despite these diverse approaches, COVID-19 vaccines are only delivered intramuscularly, whereas the nasal mucosa is the primary site of infection with SARS-CoV-2. Preclinical mucosal vaccines with intranasal or oral administration demonstrate promising results regarding mucosal IgA generation and tissue-resident lymphocyte responses against SARS-CoV-2. By mounting an improved local humoral and cell-mediated response, mucosal vaccination could be a safe and effective way to prevent infection, block transmission and contribute to reduce SARS-CoV-2 spread. However, questions and limitations remain: how effectively and reproducibly will vaccines penetrate mucosal barriers? Will vaccine-induced mucosal IgA responses provide sustained protection against infection?

Inactivated and live-attenuated seasonal influenza vaccines boost broadly neutralizing antibodies in children

The induction of broadly neutralizing antibodies (bNAbs) that target the hemagglutinin stalk domain is a promising strategy for the development of “universal” influenza virus vaccines. bNAbs can be boosted in adults by sequential exposure to heterosubtypic viruses through natural infection or vaccination. However, little is known about if or how bNAbs are induced by vaccination in more immunologically naive children. Here, we describe the impact of repeated seasonal influenza vaccination and vaccine type on induction of bNAbs against group 1 influenza viruses in a pediatric cohort enrolled in randomized controlled trials of seasonal influenza vaccination. Repeated seasonal vaccination results in significant boosting of a durable bNAb response. Boosting of serological bNAb titers is comparable within inactivated and live attenuated (LAIV) vaccinees and declines with age. These data provide insights into vaccine-elicited bNAb induction in children, which have important implications for the design of universal influenza vaccine modalities in this critical population.

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Repeated inactivated influenza vaccination boosts bNAbs

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Inactivated and live attenuated vaccines are similarly efficient at boosting bNAbs

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The magnitude of IIV and LAIV vaccine-elicited bNAb boosting declines with age

A randomized controlled trial of antibody response to 2019-20 cell-based inactivated and egg-based live attenuated influenza vaccines in children and young adults

BACKGROUND

Hemagglutination inhibition (HAI) titers to the live-attenuated influenza vaccine (LAIV4) are typically lower than its counterpart egg-based inactivated influenza vaccines (IIV). Similar comparisons have not been made between LAIV4 and the 4-strain, cell-culture inactivated influenza vaccine (ccIIV4). We compared healthy children's and young adults' HAI titers against the 2019-2020 LAIV4 and ccIIV4.

METHODS

Participants aged 4-21 years were randomized 1:1 to receive ccIIV4 (n = 100) or LAIV4 (n = 98). Blood was drawn prevaccination and on day 28 (21-35) post vaccination. HAI assays against egg-grown A/H1N1, A/H3N2, both vaccine B strains and cell-grown A/H3N2 antigens were conducted. Primary outcomes were geometric mean titers (GMT) and geometric mean fold rise (GMFR) in titers.

RESULTS

GMTs to A/H1N1, A/H3N2 and B/Victoria increased following both ccIIV and LAIV and to B/Yamagata following ccIIV (p < 0.05). The GMFR range was 2.4-3.0 times higher for ccIIV4 than for LAIV4 (p < 0.001). Within vaccine types, egg-grown A/H3N2 GMTs were higher (p < 0.05) than cell-grown GMTs [ccIIV4 day 28: egg = 205 (95% CI: 178-237); cell = 136 (95% CI:113-165); LAIV4 day 28: egg = 96 (95% CI: 83-112); cell = 63 (95% CI: 58-74)]. The GMFR to A/H3N2 cell-grown and egg-grown antigens were similar. Pre-vaccination titers inversely predicted GMFR.

CONCLUSION

The HAI response to ccIIV4 was greater than LAIV4 in this study of mostly older children, and day 0 HAI titers inversely predicted GMFR for both vaccines. Lower prevaccination titers were associated with greater GMFR in both vaccine groups.

Immune interference revisited: Impact of live-attenuated influenza vaccine prior to yellow fever vaccination

BACKGROUND

During routine mass live-attenuated influenza vaccination (LAIV) for military personnel, emergent deployment for Ebola humanitarian assistance (OUA) required mass yellow fever vaccination (YF17D), often < 4-weeks recommended timing post-LAIV-triggering concerns for immune interference. We compared YF17D seroconversion rates in personnel who received YF17D as recommended (vaccinated by guidelines [VBG]) to those who received the vaccine outside the recommended timing following LAIV (not vaccinated by guidelines [NVBG]).

METHODS

OUA deploying personnel who received LAIV simultaneously or before YF17D and had pre- and post-vaccination archived serum were included. VBG was defined as YF17D given concurrently or ≥ 30 days post-LAIV and NVBG as YF17D given 1-29 days post-LAIV. YF17D seroresponse was determined by screening ELISA confirmed with plaque reduction neutralization testing (PRNT) on positive ELISA samples. Exclusion criteria were prior YF17D and pre-vaccination YF17D positive PRNT.

RESULTS

Of the 660 personnel included, 507 were VBG and 153 were NVBG. Median age was 25 years for both groups. Men accounted for 84% of those VBG and 79% NVBG (p = 0.194). Seroconversion rates were 97.8% for VBG and 95.4% for NVBG (p = 0.15). Multivariate logistic regression revealed that YF17D on days 7-21 post-LAIV (adjusted odds ratio [aOR] 0.304, p = 0.017; confidence interval [CI] 0.114-0.810) and female sex (aOR 0.330, p = 0.026; CI 0.124-0.879) were associated with decreased seroresponse.

CONCLUSIONS

In this healthy, young adult military population, there was high seroconversion following YF17D when administered simultaneously and at various time points after LAIV. Slight decreases in seroresponse were seen in women and those receiving YF17D 7-21 days following LAIV.

Nasal vaccine as a booster shot: a viable solution to restrict pandemic?

The coronavirus disease 2019 (COVID-19) pandemic revolutionized the vaccine market and initiated the momentum for alternative routes of administration for vaccines. The intranasal route of immunization is one such possibility that appears to be the most promising since it has some significant advantages, particularly in the prevention of respiratory infection. To analyze and summarize the role of nasal vaccines over conventional vaccines during COVID-19 and the need for the nasal vaccine as a booster shot. In this narrative review, the required data was retrieved using keywords “COVID-19,” “Intranasal,” “Immunity,” “Nasal spray,” and “Mucosal” in databases including PubMed, Scopus, Embase, Science Direct, and Web of Sciences. The results of the study showed that the nasal vaccines were both effective and protective according to the current researches approaching during the COVID-19 period and the preclinical and clinical phase trials prove the intranasal vaccination elicits more robust and cross-protective immunity than conventional vaccines. In this narrative review article, mechanisms across the nasal mucosa will be briefly presented and the current status of nasal vaccines during the COVID-19 pandemic is summarized, and advantages over traditional vaccines are provided. Furthermore, after exploring the primary benefits and kinetics of nasal vaccine, the potential for consideration of nasal vaccine as a booster dose is also discussed.

Molecular and Clinical Aspects of COVID-19 Vaccines and Other Therapeutic Interventions Apropos Emerging Variants of Concern

Coronavirus disease 2019 (COVID-19) has overwhelmed the healthcare and economy of the world, with emerging new variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) posing an everlasting threat to humanity. While most COVID-19 vaccines provide adequate protective immunological response against the original SARS-CoV-2 variant, there is a pressing need to understand their biological and clinical responses. Recent evidence suggests that some of the new variants of SARS-CoV-2 evade the protection conferred by the existing vaccines, which may impede the ongoing efforts to expedite the vaccination programs worldwide. These concerns have also highlighted the importance of a pan-COVID-19 vaccine, which is currently in the making. Thus, it is imperative to have a better molecular and clinical understanding of the various COVID-19 vaccines and their immunological trajectory against any emerging variant of concerns (VOCs) in particular to break this vicious cycle. Furthermore, other treatment regimens based on cellular therapies and monoclonal antibodies should be explored systematically as an alternative and readily available option considering the possibility of the emergence of more virulent SARS-CoV-2 mutants. In this review, we shed light on the various molecular mechanisms and clinical responses of COVID-19 vaccines. Importantly, we review the recent findings of their long-term immune protection and efficacy against emerging VOCs. Considering that other targeted and effective treatments will complement vaccine therapy, we provide a comprehensive understanding of the role of cell-based therapies, monoclonal antibodies, and immunomodulatory agents as alternative and readily available treatment modalities against any emerging SARS-CoV-2 variant.

Potentiating Lung Mucosal Immunity Through Intranasal Vaccination

Yearly administration of influenza vaccines is our best available tool for controlling influenza virus spread. However, both practical and immunological factors sometimes result in sub-optimal vaccine efficacy. The call for improved, or even universal, influenza vaccines within the field has led to development of pre-clinical and clinical vaccine candidates that aim to address limitations of current influenza vaccine approaches. Here, we consider the route of immunization as a critical factor in eliciting tissue resident memory (Trm) populations that are not a target of current licensed intramuscular vaccines. Intranasal vaccination has the potential to boost tissue resident B and T cell populations that reside within specific niches of the upper and lower respiratory tract. Within these niches, Trm cells are poised to respond rapidly to pathogen re-encounter by nature of their anatomic localization and their ability to rapidly deliver anti-pathogen effector functions. Unique features of mucosal immunity in the upper and lower respiratory tracts suggest that antigen localized to these regions is required for the elicitation of protective B and T cell immunity at these sites and will need to be considered as an important attribute of a rationally designed intranasal vaccine. Finally, we discuss outstanding questions and areas of future inquiry in the field of lung mucosal immunity.

Seasonal influenza vaccination coverage and its association with COVID-19 in Saudi Arabia

Coronavirus Disease 2019 (COVID-19) pandemic is still on-going worldwide. The available information regarding the seasonal influenza vaccine (SIV) coverage during the COVID-19 pandemic and its impact on SARS-CoV-2 spread are limited. Moreover, it is argued that SIV may or may not lessen the COVID-19 severity. No previous studies have been revealed SIV coverage among COVID-19 patients and its association with COVID-19 spread and severity, especially in Saudi Arabia. Hence, this study aimed to estimate the influenza vaccine uptake in confirmed COVID-19 patients and investigate its impact on COVID-19 spread and severity. Accordingly, 1734 COVID-19 confirmed patients were included from three government hospitals in Saudi Arabia (SA). The data were collected electronically through a newly formed, self-administrated questionnaire. Among those patients, 335 were covered with SIV (19.31%), and the coverage rate of females and males was 23.4% and 15.8%, respectively. Severe COVID-19 cases were less in vaccinated patients than in non-vaccinated (2.69% vs. 3.5%, respectively). Additionally, the results showed a significant decrease in getting infected by SARS-CoV-2 after receiving SIV (P = 0.022). Even with the tremendous efforts to promote SIV uptake among the general population and high-risk groups, the SIV coverage in SA is not optimal yet. Nevertheless, there is a significant decrease in the probability of getting infected with SARS-CoV-2 after receiving SIV. Such findings with the continuous progression of the COVID-19 pandemic call for a novel approach regarding vaccination policies to increase SIV and COVID-19 vaccine uptake.

Gold-Nanostar-Chitosan-Mediated Delivery of SARS-CoV-2 DNA Vaccine for Respiratory Mucosal Immunization: Development and Proof-of-Principle

The COVID-19 pandemic is caused by the coronavirus SARS-CoV-2 (SC2). A variety of anti-SC2 vaccines have been approved for human applications, including those using messenger RNA (mRNA), adenoviruses expressing SC2 spike (S) protein, and inactivated virus. The protective periods of immunization afforded by these intramuscularly administered vaccines are currently unknown. An alternative self-administrable vaccine capable of mounting long-lasting immunity via sterilizing neutralizing antibodies would be hugely advantageous in tackling emerging mutant SC2 variants. This could also diminish the possibility of vaccinated individuals acting as passive carriers of COVID-19. Here, we investigate the potential of an intranasal (IN)-delivered DNA vaccine encoding the S protein of SC2 in BALB/c and C57BL/6J immunocompetent mouse models. The immune response to IN delivery of this SC2-spike DNA vaccine transported on a modified gold-chitosan nanocarrier shows a strong and consistent surge in antibodies (IgG, IgA, and IgM) and effective neutralization of pseudoviruses expressing S proteins of different SC2 variants (Wuhan, beta, and D614G). Immunophenotyping and histological analyses reveal chronological events involved in the recognition of SC2 S antigen by resident dendritic cells and alveolar macrophages, which prime the draining lymph nodes and spleen for peak SC2-specific cellular and humoral immune responses. The attainable high levels of anti-SC2 IgA in lung mucosa and tissue-resident memory T cells can efficiently inhibit SC2 and its variants at the site of entry and also provide long-lasting immunity.