INTRODUCTION:The mechanisms generating immunity involved in nasal vaccination for children are likely to differ significantly from both adult immunity and animal models. A deeper understanding is necessary for the development of future paediatric mucosal vaccines. Live-attenuated influenza vaccines (LAIVs) are licensed mucosal vaccines which confer protection in children against severe influenza. Beyond individual protection, mucosal vaccines can also limit transmission and colonisation, offering broader public health benefits than parenteral vaccination. We describe a protocol for an exploratory, observational study assessing systemic and mucosal responses to LAIV in healthy children. METHODS AND ANALYSIS:40 healthy participants aged 2-5 years inclusively will be recruited from the community. Researchers will conduct study visits in the participants' homes and administer a single dose of their routine, yearly LAIV and collect blood, nasal cells, nasal fluid and saliva at baseline and at day 28 post-LAIV. They will have additional nasal fluid and saliva samples conducted by caregivers on days 1, 2, 3, 4, 6, 9, 14 and 21. They will complete a daily symptom report to detect symptoms due to vaccination as well as additional upper respiratory illnesses. Samples will be analysed to detect viral load for influenza virus strains included in LAIV, coinfection and colonisation by other pathogens, as well as assess the mucosal and systemic immune response to vaccination. This study aims to advance understanding of mucosal immunity mechanisms in children following live-attenuated influenza vaccination. This knowledge could help inform the development of future mucosal vaccines for children, potentially increasing both effectiveness, ease of delivery and tolerability in this vulnerable population. ETHICS AND DISSEMINATION:This protocol has been reviewed by the sponsor, collaborators and external peer reviewers. Ethical approval for this study has been obtained from the South Central - Hampshire B Research Ethics Committee (REC ref 24/SC/0251). Informed parental consent will be obtained prior to any study intervention. The results will be disseminated via publication in a peer-reviewed journal and presentation at international conferences. STUDY REGISTRATION:ISRCTN87260269 (https://doi.org/10.1186/ISRCTN87260269).

The local and systemic symptoms that follow vaccination, collectively referred to as reactogenicity, are common, yet the mechanisms underlying individual variability remain poorly understood. Through longitudinal immune profiling of vaccinated individuals and mechanistic studies in mice, we identified key immunological determinants of reactogenicity induced by mRNA vaccines. Systemic adverse events were associated with stronger interferon and pro-inflammatory responses after the second dose of a COVID-19 mRNA vaccine, which were also correlated with the magnitude of the antigen-specific adaptive responses. This heightened inflammation occurred within 24 hours of vaccination, originated primarily from the injection site, and was characterized by enhanced recruitment and activation of myeloid cells, particularly monocytes. Two mechanisms contributed to this response: early interferon production by muscle T cells generated after the first dose and Fcγ receptor-dependent chemokine induction by vaccine antigen-specific antibodies. Consistently, serum antibody levels before vaccination correlated positively with reactogenicity. In addition to this local amplification mechanism, variability in reactogenicity was influenced by the baseline immune state, given that individuals with a preexisting interferon-stimulated gene signature in monocytes, detectable at both transcriptomic and epigenetic levels, were more prone to systemic symptoms. Together, our findings revealed molecular and cellular mechanisms driving vaccine reactogenicity, providing a framework for the design of less reactogenic vaccines.

OBJECTIVES:Nearly a million people have received the recombinant vesicular stomatitis virus-based vaccine expressing the surface glycoprotein of Ebola virus (rVSVΔG-ZEBOV-GP), whose immune durability is unknown. We evaluated the safety and immunogenicity of the DNA vaccine candidate INO-4201 in volunteers primed with the rVSVΔG-ZEBOV-GP vaccine. METHODS:This investigator-initiated phase Ib double-blind, placebo-controlled, single-centre trial randomly assigned healthy adults (≥18 years) primed with rVSVΔG-ZEBOV-GP to intradermal INO-4201 (1 mg) or placebo (4:1), both followed with electroporation. The coprimary outcome was incidence of adverse events at 14 days and geometric mean EBOV-GP-binding antibody titres (GMT) at 28 days (clinicaltrials.gov NCT04906629). RESULTS:Forty-six participants were enrolled. Median age was 52 years (interquartile range 44-57); 26 (57%) were male. Thirty-six participants received INO-4201 and 10 participants received placebo. No serious adverse events occurred. There was little reactogenicity. At 14 days, 20 of 36 (56%) vaccinees versus 5 of 10 (50%) placebo recipients (relative risk 1.11 [95% CI 0.56-2.20]) experienced adverse events. Peak T-cell responses were significantly increased in INO-4201 recipients (median percentage of CD4 cells producing interferon-gamma at postboost peak versus day 0: 0.09 [range 0.00-14.48] versus 0.00 [0.00-1.33], p 0.004). Filovirus Animal Non-Clinical Group-based EBOV-GP-binding titres were significantly higher after boosting for vaccinees at all time points (GMT at 4 weeks versus day 0: 3221.7 [95% CI 2629.8-3946.8] vs 704.3 [513.8-965.3]). Neutralizing antibody titres were also significantly higher after boosting for vaccinees at all time points measured (GMT at 4 weeks versus day 0: 21.3 [95% CI 13.8-32.7] versus 2.4 [1.5-3.9]). CONCLUSIONS:In adults primed with rVSVΔG-ZEBOV-GP, INO-4201 demonstrated favourable safety and significant immunogenicity.

Combination adjuvants enhance vaccine immunogenicity by integrating multiple immunostimulatory signals that shape both innate and adaptive immune responses. In this review, we summarize the clinical evidence supporting the added value of combination adjuvants, including aluminum-Toll-like receptor ligand formulations, oil-in-water emulsions containing immunostimulatory molecules, and saponin-based systems. We further discuss how the most recent mechanistic studies have shown that combination adjuvants act through additive or synergistic effects, engaging distinct molecular and cellular pathways to shape innate immune activation. Moreover, we propose that mRNA vaccines represent a new class of functional combination adjuvants, integrating both mRNA sensing and lipid nanoparticle-driven inflammation. Together, the current evidence supports the value of combination adjuvants in optimizing vaccine responses and underscores the need to continuously understand their mode of action to enable rational adjuvant design.

People living with HIV-1 (PLWH) are a population at higher risk for communicable disease and therefore a target group for vaccination. Owing to the success of anti-retroviral therapy, PLWH live longer, but face new challenges related to ageing, which add to their underlying immunodeficiencies. We review here the immune dysregulations occurring with chronic HIV-1 infection and ageing in the era of antiretroviral therapy, focusing on cellular mechanisms that can explain the lower immune response to most vaccines in older treated PLWH, and we discuss potential developments to improve vaccination strategies in this specific population.

While Influenza Virus and Respiratory Syncytial Virus (RSV) are considered as a significant health burden in children, Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) causes milder diseases in this age group compared to adults. To investigate the involvement of the upper respiratory tract human airway epithelium (HAE) in this pattern, we established an in-house model of reconstituted HAE cultured in air-liquid interface from nasal swabs of children and adults and characterised it before and after ex vivo respiratory viral infections using focused and unbiased approaches. Fully differentiated paediatric HAE exhibited an increasing induction level of genes related to mucociliary clearance, while higher expression of innate immune pathways was found in the ones from adults. While similar viral replication kinetics in both age groups were shown for SARS-CoV-2, Influenza A Virus (IAV), RSV and Rhinovirus (RV) infection, transcriptomic analysis showed stronger and earlier induction of IFN-related pathways in SARS-CoV-2-infected HAE from children compared to IAV, RSV and RV. IAV and RSV had the weakest innate immune response increase in HAE from children versus adults. RV infection showed an intermediate pattern, resembling SARS-CoV-2 more than RSV or IAV. Our work demonstrates a distinct sensing of SARS-CoV-2 compared to other respiratory viruses ex vivo, which may contribute to the milder course of disease in SARS-CoV-2 infected children and argues for a role of early virus-HAE interaction in shaping viral pathogenesis. Furthermore, we show that innate immune responses towards respiratory viruses are virus-specific and differ between age groups. Hence, findings on SARS-CoV-2 cannot be extrapolated to other respiratory viruses. ### Competing Interest Statement The authors have declared no competing interest.

Measles is one of the most contagious vaccine preventable diseases, causing severe complications and deaths globally. While vaccination with a measles-containing vaccine (MCV) has prevented millions of measles deaths, recent trends, especially from low- and middle-income countries, are discouraging. Measles cases have increased since 2021 as MCV coverage has decreased; and an estimated 107,500 measles deaths, mostly in children under-five years, occurred in 2023. Thus, a renewed focus on proven and innovative strategies to control measles is needed. The World Health Organization (WHO) recommends a first MCV dose administered at 9-15 months of age (routine MCV1), however MCV1 below 9 months of age (early MCV1) may increase vaccination coverage because uptake of all vaccines tends to be higher the younger the child, and this might protect vulnerable infants earlier in life. However, due to concerns about possible reduced vaccine performance, early MCV1 is not routinely recommended by WHO. WHO hosted an informal technical consultation on December 6-7, 2023, in Geneva, Switzerland to evaluate recent evidence on early MCV1 and identify evidence gaps for policy making. The recent evidence suggests a robust humoral immune response shortly after early MCV1 at 5-8 months of age. Immune blunting of a routine second MCV dose (e.g., MCV2) after early MCV1 was not demonstrated in the presented data. However, 3-7 years after MCV1, children receiving early MCV1 had lower measles antibodies than children receiving routine MCV1, suggesting faster waning of immunity. The totality of evidence on immune blunting remains inconsistent. Meeting participants thought more data are needed before revisiting WHO's current recommendation for a potential revision. Evidence gaps include: understanding measles disease burden and severity in infants; early MCV1 effectiveness and duration; vaccine-induced cellular immunogenicity; whether measles in infants is acquired from other infants or older children or adults; and blunting of routine MCV2. Addressing evidence gaps through targeted studies and measles outbreak investigations, as well as evaluations of country-level introductions of early MCV1 are warranted. Ensuring high MCV1 and MCV2 coverage remains the priority in measles control.

BackgroundTreatment with anti-CD20 antibodies (rituximab) is used in both adults and children to treat various autoimmune and oncological diseases. Rituximab depletes B CD20+ cells and, thereby, antibody response to vaccines. This study aimed to examine the antibody response to mRNA-based COVID-19 vaccines in children aged 5-18 years undergoing rituximab treatment compared to healthy matched children.MethodsBetween 31 January and 18 July 2022, we conducted a prospective observational study at the Geneva University Hospitals, enrolling children aged 5-18 years under rituximab treatment who had received two mRNA-based SARS-CoV-2 vaccine doses. Controls were healthy volunteers with no significant medical conditions. Exclusion criteria included a recent SARS-CoV-2 infection. Blood samples were collected at day 60 (+/- 30) and day 270 (+/- 90) after the second vaccination.ResultsThe rituximab-treated group exhibited significantly lower levels of antibodies specific to the anti-receptor binding domain (RBD) of the SARS-CoV-2 spike (S) protein than healthy controls at 60 (+/- 30) days after the second vaccine dose (geometric mean concentration: 868.3 IU/mL in patients and 11,393 IU/mL in controls; p = .008). However, patients with a rituximab-to-vaccine interval shorter than 6 months and with evidence of a past infection (based on positive anti-N antibody levels) had a high level of anti-RBD antibodies.ConclusionA past infection with SARS-CoV-2 may induce anti-RBD-specific memory B cells that can be re-activated by SARS-CoV-2 vaccination, even after rituximab-induced B-cell depletion. This suggests that it is possible to vaccinate earlier than 6 months after rituximab to develop a good antibody response, especially in the case of past SARS-CoV-2 infection.

Background The burden of herpes zoster (shingles) virus and associated complications, such as post-herpetic neuralgia, is higher in older adults and has a significant impact on quality of life. The incidence of herpes zoster and post-herpetic neuralgia is increased in people living with HIV (PLWH) compared to an age-matched general population, including PLWH on long-term antiretroviral therapy (ART) with no detectable viremia and normal CD4 counts. PLWH – even on effective ART may- exhibit sustained immune dysfunction, as well as defects in cells involved in the response to vaccines. In the context of herpes zoster, it is therefore important to assess the immune response to varicella zoster virus vaccination in older PLWH and to determine whether it significantly differs to that of HIV-uninfected healthy adults or younger PLWH. We aim at bridging these knowledge gaps by conducting a multicentric, international, non-randomised clinical study (SHINGR’HIV) with prospective data collection after vaccination with an adjuvant recombinant zoster vaccine (RZV) in two distinct populations: in PLWH on long-term ART (> 10 years) over 50 years of and age/gender matched controls. Methods We will recruit participants from two large established HIV cohorts in Switzerland and in France in addition to age-/gender-matched HIV-uninfected controls. Participants will receive two doses of RZV two months apart. In depth-evaluation of the humoral, cellular, and innate immune responses and safety profile of the RZV will be performed to address the combined effect of aging and potential immune deficiencies due to chronic HIV infection. The primary study outcome will compare the geometric mean titer (GMT) of gE-specific total IgG measured 1 month after the second dose of RZV between different age groups of PLWH and between PLWH and age-/gender-matched HIV-uninfected controls. Discussion The SHINGR’HIV trial will provide robust data on the immunogenicity and safety profile of RZV in older PLWH to support vaccination guidelines in this population. Trial registration ClinicalTrials.gov NCT05575830. Registered on 12 October 2022. Eu Clinical Trial Register (EUCT number 2023-504482-23-00).

Vaccine adjuvants are thought to work by stimulating innate immunity in the draining lymph node (LN), although this has not been proven in humans. To bridge the data obtained in animals to humans, we have developed an in situ human LN explant model to investigate how adjuvants initiate immunity. Slices of explanted LNs were exposed to vaccine adjuvants and revealed responses that were not detectable in LN cell suspensions. We used this model to compare the liposome-based AS01 with its components, monophosphoryl lipid A (MPL) and QS-21, and TLR ligands. Liposomes were predominantly taken up by subcapsular sinus-lining macrophages, monocytes, and DCs. AS01 induced DC maturation and a strong proinflammatory cytokine response in intact LN slices but not in dissociated cell cultures, in contrast to R848. This suggests that the onset of the immune response to AS01 required a coordinated activation of LN cells in time and space. Consistent with the robust immune response observed in older adults with AS01-adjuvanted vaccines, the AS01 response in human LNs was independent of age, unlike the response to R848. This human LN explant model is a valuable tool for studying the mechanism of action of adjuvants in humans and for screening new formulations to streamline vaccine development.

Background New onsets of chronic urticaria (CU) have been reported after repeated immunizations, mainly with the Moderna mRNA-1273 vaccine (Spikevax) Objective This study aims to evaluate patients with CU after COVID-19 mRNA vaccination. The contribution of SARS-Cov2 infection, atopy and IgE against the vaccine was analyzed. Methods We monitored the features of patients who developed CU after vaccination in the Canton of Vaud through two surveys conducted in 2022 and 2023. Fifty individuals with CU underwent blood tests, and their results were compared with individuals without a history of urticaria (N=135). The presence of anti-vaccine IgE was detected with basophil activation tests (BAT). We assessed anti-SARS-Cov2 humoral response, and the presence of IgEs against common respiratory allergens (Phadiatop) as a surrogate for atopy. Results Post-vaccination CU occurred after a median interval of 10 days and significantly more after the Spikevax booster, affecting middle-aged individuals (median 41, 66% females). In 2023, CU was still active in 53% of the cases. Inducible forms of CU, primarily dermographism, were reported in 54% (2022) and 61% (2023) of the cases. BAT positivity was not specific to CU, anti-nucleocapsid positivity, or atopy but was significantly associated with higher anti-spike neutralizing activities and younger age. Four CU patients tolerated an additional dose of mRNA vaccine with no disease exacerbation/recurrence. Conclusion The Spikevax booster induced anti-vaccine IgE independently of CU, the latter being not directly associated with COVID-19 infection nor atopy. The tolerance to a new booster in 4/4 patients suggests that the Spikevax vaccine indirectly triggered CU in predisposed individuals.

Next-generation COVID-19 vaccines are being developed to expand the breadth of coverage against existing and future variants and to extend the duration of protection. Prime-2-CoV_Beta is an orf virus (ORFV) based multi-antigen COVID-19 vaccine that co-expresses Spike (S) and Nucleocapsid (N) antigens. The safety and immunogenicity of Prime-2-CoV_Beta is investigated in a phase 1 first-in-human (FIH) dose-finding trial (ORFEUS study, ClinicalTrials.gov: NCT05367843). Participants of two age groups (18-55 and 65-85 years) who previously completed at least two doses of mRNA vaccines were enrolled and sequentially assigned to different dose groups to receive one intramuscular dose of 3 x 105, 3 x 106, 1.5 x 107, or 3 x 107 plaque-forming units (PFU) of Prime-2-CoV_Beta on day 1 and a second dose on day 29. Here, we report safety and immunogenicity data collected up to 6 months after the first study vaccination. Prime-2-CoV_Beta is safe and well tolerated and elicits immune responses at higher dose levels in participants aged 18-55. A single dose of 3 x 107 PFU boosted binding and cross-neutralizing antibody responses that are maintained through 6 months after the first booster vaccination. Polyfunctional S-specific CD4+ and CD8+ T cell responses are observed after vaccination. No pre-existing or vaccine-induced neutralizing anti-vector antibodies are detected. Our findings highlight the potential of the ORFV vector as a safe platform for future vaccine design, which provides the ability to deliver multiple antigens and allows for repeat immunization.

The adjuvant AS01 plays a key role in the immunogenicity of several approved human vaccines with demonstrated high efficacy. Its adjuvant effect relies on activation of the innate immune system. However, specific effects of AS01-adjuvanted vaccines on innate cell function and epigenetic remodeling, as described for Bacille Calmette-Guérin (BCG) and influenza vaccines, are still unknown. We assessed the long-term functional and epigenetic changes in circulating monocytes and dendritic cells induced by a model vaccine containing hepatitis B surface antigen and AS01 in healthy adults (NCT01777295). The AS01-adjuvanted vaccine, but not an Alum-adjuvanted vaccine, increased the number of circulating monocytes and their expression of human leukocyte antigen (HLA)–DR, which correlated with the magnitude of the memory CD4 + T cell response. Single-cell analyses revealed epigenetic alterations in monocyte and dendritic cell subsets, affecting accessibility of transcription factors involved in cell functions including activator protein-1 ( AP-1 ), GATA , C/EBP , and interferon regulatory factor. The functional changes were characterized by a reduced proinflammatory response to Toll-like receptor activation and an improved response to interferon-γ, a cytokine critical for the adjuvant’s mode of action. Epigenetic changes were most evident shortly after the second vaccine dose in CD14 + monocytes, for which accessibility differences of some transcription factors could persist for up to 6 months postvaccination. Together, we show that reprogramming of monocyte subsets occurs after vaccination with an AS01-adjuvanted vaccine, an effect that may contribute to the impact of vaccination beyond antigen-specific protection.

BackgroundDuring the last decade Ebola virus has caused several outbreaks in Africa. The recombinant vesicular stomatitis virus-vectored Zaire Ebola (rVSVΔG-ZEBOV-GP) vaccine has proved safe and immunogenic but is reactogenic. We previously identified the first innate plasma signature response after vaccination in Geneva as composed of five monocyte-related biomarkers peaking at day 1 post-immunization that correlates with adverse events, biological outcomes (haematological changes and viremia) and antibody titers. In this follow-up study, we sought to identify additional biomarkers in the same Geneva cohort and validate those identified markers in a US cohort.MethodsAdditional biomarkers were identified using multiplexed protein biomarker platform O-link and confirmed by Luminex. Principal component analysis (PCA) evaluated if these markers could explain a higher variability of the vaccine response (and thereby refined the initial signature). Multivariable and linear regression models evaluated the correlations of the main components with adverse events, biological outcomes, and antibody titers. External validation of the refined signature was conducted in a second cohort of US vaccinees (n=142).ResultsEleven additional biomarkers peaked at day 1 post-immunization: MCP2, MCP3, MCP4, CXCL10, OSM, CX3CL1, MCSF, CXCL11, TRAIL, RANKL and IL15. PCA analysis retained three principal components (PC) that accounted for 79% of the vaccine response variability. PC1 and PC2 were very robust and had different biomarkers that contributed to their variability. PC1 better discriminated different doses, better defined the risk of fever and myalgia, while PC2 better defined the risk of headache. We also found new biomarkers that correlated with reactogenicity, including transient arthritis (MCP-2, CXCL10, CXCL11, CX3CL1, MCSF, IL-15, OSM). Several innate biomarkers are associated with antibody levels one and six months after vaccination. Refined PC1 correlated strongly in both data sets (Geneva: r = 0.97, P < 0.001; US: r = 0.99, P< 0.001).ConclusionEleven additional biomarkers refined the previously found 5-biomarker Geneva signature. The refined signature better discriminated between different doses, was strongly associated with the risk of adverse events and with antibody responses and was validated in a separate cohort.

BackgroundNew onsets of chronic urticaria (CU) have been reported after repeated immunizations, mainly with the Moderna mRNA-1273 vaccine (Spikevax). This study aims to evaluate patients with CU after COVID-19 mRNA vaccination. The contribution of SARS-Cov2 infection, atopy and IgE against the vaccine was analyzed.MethodsWe monitored the features of patients who developed CU after vaccination through two surveys conducted in 2022 and 2023. Fifty individuals with CU underwent blood tests, and their results were compared with individuals without a history of urticaria (N = 135). The presence of anti-vaccine IgE was tested in 185 individuals with basophil activation tests (BAT). We assessed anti-SARS-Cov2 humoral response, and the presence of IgEs against common respiratory allergens (Phadiatop) as a surrogate for atopy.ResultsPost-vaccination CU occurs after a median interval of 10 days and significantly more after the Spikevax booster, affecting middle-aged individuals (median 41, 66% females). In 2023, CU was still active in 53% of the cases. Inducible forms of CU, primarily dermographism, are reported in 54% (2022) and 61% (2023) of the cases. BAT positivity is not specific to CU, anti-nucleocapsid positivity, or atopy but is significantly associated with higher anti-spike neutralizing activities and younger age. Four CU patients tolerate an additional dose of mRNA vaccine with no disease exacerbation/recurrence.ConclusionsThe spikevax booster induces anti-vaccine IgE independently of CU, the latter being not directly associated with COVID-19 infection nor atopy. The tolerance to a new booster in 4/4 patients suggests that the Spikevax vaccine indirectly triggers CU in predisposed individuals. Urticaria is an itchy transient skin rash which can become in some cases recurrent and chronic. Repeated immunizations with COVID-19 mRNA vaccines can rarely lead to the development of chronic urticaria (CU), on average 10 days after vaccination. Here, we monitored people who developed CU after vaccination. One year following vaccination 53% of people still had CU. CU after vaccination was not directly associated with COVID infection, allergic predisposition or other effects of vaccination. Re-exposure to the vaccine was safe and well tolerated in four patients with vaccine-related CU suggesting an absence of a direct causality between the vaccine and CU. Therefore, managing CU post-vaccination should follow previously established guidelines as for other forms of CU. Schwab et al. evaluate patients with chronic urticaria (CU) in relation to COVID-19 infection and mRNA vaccination. CU post-vaccination was not directly associated with COVID infection nor atopy and initiates independent of vaccine sensitization.