Shigellosis is one of the leading causes of diarrhoeal disease worldwide. It mostly affects children under 5 years and elderly persons over 70 years in low- and middle-income countries (LMICs). The high disease incidence in LMICs and the rise of antimicrobial resistance have prompted efforts to develop novel vaccines against shigellosis. Several multicomponent vaccines are currently under development; to date, however, no correlate of protection against shigellosis has been defined. The Serum Bactericidal Activity assay (SBA) is regularly applied to measure the complement-mediated functional activity of vaccine-elicited antibodies for other bacterial species. To facilitate the evaluation of Shigella candidate vaccines and to support licensing, a high-throughput SBA, based on luminescence readout (L-SBA), has been developed to test antibody functionality. In this study, the assay has been transferred to a Clinical Research Organization (CRO) and qualified for five epidemiologically relevant Shigella serotypes (S. flexneri 2a, 1b, 3a, 6 and S. sonnei) using pooled human serum samples. The repeatability, intermediate precision and linearity of the assay were confirmed, together with the ability of the assay to detect serotype specific Shigella antibody activity. This study confirms that the L-SBA method can be performed by different laboratories and is suitable for testing multicomponent vaccine candidates against shigellosis.

BACKGROUND:ABO blood group has been associated with SARS-CoV-2 susceptibility. Little data exist regarding the impact of ABO and Rhesus (Rh[D]) type on breakthrough infections and antibody responses following SARS-CoV-2 booster vaccination. METHODS:This multicenter, population-based cohort study includes individuals ≥ 18 years who received a booster vaccination against SARS-CoV-2. Antibody levels against SARS-CoV-2 receptor binding domain (RBD) and neutralizing antibodies against wild-type (WT) virus and Omicron variant were assessed at baseline, after 4 weeks and after 6 months. At 6 months follow-up, self-reported ABO and Rh(D) type, time to, and severity of breakthrough infections were collected. RESULTS:In total, 3066 participants (mean age 49 [35-59], 62% female) were included in multivariable regression models, showing no association of anti-RBD and neutralizing antibodies against wild-type and Omicron variant with ABO or Rh(D) 4 weeks after booster vaccination. Time-dependent Cox regression analysis showed significantly lower rates of breakthrough infections in patients with AB (hazard ratio [HR] 0.67 [0.50-0.90]; p = 0.008) compared to O, even after adjustment for relevant covariates and a trend for blood group B (HR 0.82 [0.66-1.01]; p = 0.06) compared to O; there were no associations between Rh(D) and breakthrough infection rates or between observed (asymptomatic to moderate) COVID-19 symptom severity and ABO or Rh(D) blood group. CONCLUSIONS:ABO or Rh(D) blood group was not associated with COVID-19 severity or antibody responses following SARS-CoV-2 vaccination. Breakthrough infections were least common in blood groups AB and B. Although our data do not support previously discussed protective effects of anti-A/B/Rh(D) agglutinins, differences in ABO group appear relevant for Omicron transmission.

Influenza is an infectious respiratory disease that has significant morbidity and a high mortality rate. The immune responses induced against both seasonal and potentially pandemic strains of the influenza virus are of fundamental importance. The microneutralization (MN) assay is an extremely important virological test for the evaluation of vaccines, and therefore of the antibody response. However, there is not always a correspondence between the results obtained from the same samples, owing to the difficult readout of the cytopathic effect (CPE) in the case of live viruses and the subjectivity of interpretation by operators. Moreover, if the test is combined with the Enzyme-Linked Immunosorbent Assay (ELISA) technique, the process is laborious. Here, we present a microneutralization assay that uses the PrestoBlue® reagent as a colorimetric CPE-based method. We evaluated the performance of this test on multiple strains of influenza virus by using human serum samples from a commercial panel and comparing both subjective (inverted microscope) and objective (spectrophotometer) readouts. Our results suggest that this colorimetric method for assessing CPE in microneutralization tests is more sensitive than the subjective method, while yielding comparable titers. This assay allows accurate and repeatable reading of the results, thereby reducing the possible uncertainty of the readout and speeding up the process.

Influenza D virus (IDV) was first isolated in 2011 from a swine with respiratory disease symptoms in the United States. Epidemiological and serological evidence suggests that cattle are the natural reservoir of IDV, with periodic spillover events to other animal hosts. This study investigated the seroprevalence of two IDV lineages, D/660 and D/OK, among cattle workers in Southern Italy between 2023 and 2024 to better characterize the zoonotic exposure risk in this occupational setting. A control group from the same geographical area was also included. Serum samples were tested by hemagglutination inhibition and virus neutralization (VN) assays. Overall, 42.9% (60/140) of cattle workers were positive at least to one of the two IDV lineages. Moreover, 39.3% (55/140) were positive for D/660 and 34.3% (48/140) for D/OK, with all but one positive result confirmed by VN assay. In the control group, tested only for D/660, a significantly higher seroprevalence was observed, with 65.0% (39/60) testing positive. These findings suggest that IDV exposure is not restricted to occupational settings involving direct contact with cattle and underscore the importance of incorporating IDV into current influenza surveillance programs.

Dogs have not typically been considered natural hosts for influenza viruses. However, two canine influenza subtypes, H3N8 and H3N2, have been associated with infection in this species, posing a potential zoonotic threat. In this study, a serological investigation was conducted to assess the seroprevalence of human seasonal influenza viruses (type A and B), as well as canine and avian influenza A viruses, and the H7N1 virus, in a population of adult household dogs. A total of 256 serum samples were analysed by the hemagglutination inhibition and virus neutralization assays. The seroprevalence rates were 0.78% and 77.34% for human seasonal H1N1 and H3N2 influenza viruses; 0.39% for both the B Yamagata and B Victoria lineages; and 1.17% for H7N1 virus. None of the samples tested positive for avian or canine viruses. These findings suggest that household dogs can be exposed to human seasonal influenza viruses, emphasizing the importance of continued surveillance of influenza viruses within canine populations.

BACKGROUND:Relative accuracy (RA) and linearity are distinct validation characteristics in bioassay validation, yet quantitative relationships between their acceptance criteria are rarely defined. This study investigated how predefined RA tolerances determine admissible linearity acceptance ranges. RESEARCH DESIGN AND METHODS:A theoretical framework for assessing dilutional linearity was established using a b-fold serial dilution design. Relative accuracy was defined as the ratio of observed to expected geometric means, evaluated against a tolerance threshold (θ). Linearity was determined through linear regression of logb(GMobserved) against logb(Dilution). Analytical expressions were derived for acceptable slope intervals based on θ and the number of valid dilution levels. A simulated bioassay dataset illustrated its application. RESULTS:Analytical derivations showed that admissible slope intervals depend exclusively on θ and the number of valid dilution levels. The resulting limits were invariant with respect to both the initial geometric mean and the dilution fold factor. In the illustrative example, the proposed framework supported acceptance of linearity while retaining all valid dilution levels. CONCLUSIONS:This study provides a mathematically consistent method for deriving linearity acceptance criteria directly from predefined RA requirements. Although illustrated using simulated data, it offers a tool for dilution-based bioassay validation and may support more coherent validation decisions.

Recent outbreaks of highly pathogenic human RNA viruses from probable zoonotic origin have highlighted the relevance of epidemic preparedness as a society. However, research in vaccinology and virology, as well as epidemiologic surveillance, is often constrained by the biological risk that live virus experimentation entails. These also involve expensive costs, time-consuming procedures, and advanced personnel expertise, hampering market access for many drugs. Most of these drawbacks can be circumvented with the use of pseudotyped viruses, which are surrogate, non-pathogenic recombinant viral particles bearing the surface envelope protein of a virus of interest. Pseudotyped viruses significantly expand the research potential in virology, enabling the study of non-culturable or highly infectious pathogens in a safer environment. Most are derived from lentiviral vectors, which confer a series of advantages due to their superior efficiency. During the past decade, many studies employing pseudotyped viruses have evaluated the efficacy of vaccines or monoclonal antibodies for relevant pathogens such as HIV-1, Ebolavirus, Influenza virus, or SARS-CoV-2. In this review, we aim to provide an overview of the applications of pseudotyped viruses when evaluating the neutralization capacity of exposed individuals, or candidate vaccines and antivirals in both preclinical models and clinical trials, to further help develop effective countermeasures against emerging neutralization-escape phenotypes.

Influenza vaccines are the primary strategy to prevent severe influenza disease; however, their efficacy is often suboptimal, particularly in older adults (OAs). LiteVax Adjuvant (LVA), a novel adjuvant containing carbohydrate fatty-acid monosulphate ester (CMS) as the active ingredient, has demonstrated a favourable safety profile and enhanced immunogenicity when combined with a low-dose seasonal influenza vaccine in adults aged 18 to 50 years in a first-in-human phase 1 study. The present study investigates the reactogenicity and immunogenicity of CMS-based adjuvanted seasonal influenza vaccine in OAs, with a comparison to responses in younger adults (YAs). In this phase 1b, double-blind, active-controlled clinical trial, 36 YAs (18–50 years) and 48 OAs (≥60 years) were randomized (1:1:1) to receive either 0.5 mg or 1 mg LVA combined with VaxigripTetra, or VaxigripTetra alone. Solicited adverse events (AEs) were recorded using an electronic diary for 7 days following vaccination. Hemagglutination inhibition (HI) titers against four influenza strains were measured at baseline (pre-vaccination) and at 7-, 28-, and 180-days post-vaccination. All 24 YAs and 31 out of 32 OAs receiving CMS-based adjuvanted vaccines reported pain post-vaccination, compared to 8/12 YAs and 4/16 OAs receiving VaxigripTetra. Systemic AEs were more frequently reported among YAs receiving CMS-based adjuvanted vaccines (22/24) compared to those receiving VaxigripTetra (8/12). In OAs, the number of systemic AEs was similar regardless of CMS-based adjuvant administration. Most AEs were mild to moderate and resolved within 3 days. Both CMS-based adjuvanted formulations elicited increased HI titers at Day 7, peaking at Day 28, with a decline thereafter that remained above baseline at Day 180. In YAs, HI titers were comparable between the CMS-based adjuvanted and non-adjuvanted vaccines across all strains and timepoints. In contrast, CMS-based adjuvanted vaccination in OAs induced higher HI titers at Days 28 and 180 for all influenza strains tested. LVA shows an acceptable safety profile in both age cohorts and enhances humoral immune responses in older adults. The 1 mg dose of LVA was more immunogenic, highlighting its potential utility in this target population. Future research will focus on elucidating the mechanisms underlying the immunostimulatory effect of the CMS-based adjuvant.

Background:Authorized COVID-19 vaccines require boosters for continued protection; however, the lack of cross-platform compatible boosters creates practical challenges to keeping populations protected. Methods:This Phase 3, multicenter, international, randomized, active-controlled trial compared UB-612 as a third-dose heterologous booster to BNT162b2, ChAdOx1-S, or BBIBP-CorV homologous boosters in healthy subjects aged ≥16 years. Participants were randomly assigned 1:1 to receive a single intramuscular injection of UB-612 or an active comparator matching the primary dose, and were stratified for age, sex, N-protein seropositivity, and time since the last dose of their primary series COVID-19 vaccination. The primary objective was to show non-inferiority of neutralizing antibody geometric mean titer (GMT) against live SARS-CoV-2 Wuhan strain after boosting with UB-612 or each of the licensed platform vaccines. Secondary and exploratory objectives covered short and long-term antibody responses. The safety analysis addressed subject and investigator reported adverse events. The study was registered on ClinicalTrials.gov, NCT05293665, and completed on September 12, 2023. Findings:Between March 22 and September 9, 2022, 469 subjects received UB-612 as a heterologous booster, and 467 received BNT162b2 (n = 204), ChAdOx1-S (n = 95), or BBIBP-CorV (n = 168) as homologous boosters. Over 90% of all subjects were positive for N-protein antibody at baseline. When compared to the respective homologous booster response, UB-612 stimulated Wuhan and Omicron BA.5 neutralizing antibody responses that were non-inferior, thus meeting all primary and secondary immunogenicity endpoints of the study. Importantly, UB-612 demonstrated superiority in neutralizing antibody GMT and seroresponse rates compared to ChAdOx1-S and BBIBP-CorV. UB-612 was also effective in stimulating neutralizing antibodies against a more recent Omicron XBB1.5 strain. Long-term immunity analysis through 6- and 12-month follow-ups favored UB-612 over ChAdOx1-S and BBIBP-CorV and supported comparable immunity to BNT162b2. All vaccines were well tolerated and had similar safety profiles. Interpretation:In a pivotal Phase 3 study, UB-612 demonstrated the potential for broad use as a cross-platform heterologous booster, restoring protective immunity in adults previously vaccinated with mRNA, adenovirus-vectored, or inactivated virus-based COVID-19 vaccines. Funding:The study was co-funded by the Coalition for Epidemic Preparedness Innovations (CEPI) and Vaxxinity.

A randomized, placebo-controlled, crossover, double-blind, phase II/III study was conducted to evaluate the immunogenicity, safety, and tolerability of a recombinant booster vaccine (ARVAC) containing the SARS-CoV-2 spike protein receptor binding domain in three versions: ARVACGamma, ARVACOmicron, and ARVACBivalent in adults with ≤3 previous SARS-CoV-2 booster doses. Primary endpoint was seroconversion rate of neutralizing antibodies compared to placebo and to a > 75 % seroconversion rate to vaccine antigen homologous variants. All vaccine versions significantly increased seroconversion rates to SARS-CoV-2 variants compared to placebo. In participants aged 18-60 years, all versions met the primary endpoint; in those over 60 years old, ARVACOmicron and ARVACBivalent met this endpoint. No vaccine-related serious adverse events were recorded, and most adverse events were mild. Plasma levels of anti-spike-specific IgG and anti-S1-specific IgA in saliva increased in participants receiving any vaccine. The increase in plasma neutralizing antibodies induced by the vaccine was independent of the number of previous booster doses (0, 1 or 2), the primary vaccine platform (adenovirus, single-dose adenovirus, mRNA, inactivated virus, heterologous vaccination, and virus-like particle [VLP]) and the history of previous COVID-19. The neutralizing Ab response induced by the vaccine in healthy participants was similar to that triggered in participants with underlying medical conditions associated with an increased risk of severe COVID-19. ARVACBivalent induced high seroconversion rates (>90 %) against multiple variants and was superior to other ARVAC-versions. It increased neutralizing antibodies against SARS-CoV-2 variants (Ancestral, Gamma, Omicron, XBB and JN.1) and SARS-CoV-1. (NCT05752201).

Introduction:Monkeypox (mpox), an endemic zoonotic viral disease in Central and Western Africa, gained international attention in 2022 when clade IIb of the Monkeypox virus (MPXV) spread outside Africa, prompting the World Health Organization (WHO) to declare it a Public Health Emergency of International Concern (PHEIC). Although the PHEIC was lifted in 2023 due to declining global cases, a resurgence caused by clade Ib has reinstated the emergency status. Current mpox vaccines, based on live-attenuated or modified vaccinia virus (VACV), have historical use in smallpox prevention. Understanding the humoral immune response triggered by mpox vaccination and infection, as well as identifying correlates of protection, remain however critical. Methods:In a previous study, we evaluated the neutralizing antibody response of 1,000 individuals, half born before the cessation of smallpox vaccination in Italy (pre-1975) and half after (post-1979). Higher neutralizing antibody titers against MPXV and VACV were observed in subjects vaccinated against smallpox, indicating a cross-reactive immunity to MPXV. This study further investigated these findings by analyzing the IgG response to five MPXV and five VACV antigens in a subset of the previously tested cohort, using a multiplex immunoassay. Serum samples from 370 individuals were grouped by neutralization profile (negative for both MPXV and VACV, positive for both viruses, negative for MPXV but positive for VACV, and vice versa) and age (born before 1975 and after 1979). Results:Our data revealed stronger immune responses to specific antigens, particularly A35R/A33R and B6R/B5R, with MPXV-specific binding antibodies showing greater cross-reactivity compared to VACV ones. Furthermore, individuals born before 1975, vaccinated against smallpox, exhibited stronger binding and neutralizing antibody responses, as opposed to people born after 1979 in whom neutralization titers were lower. This suggests that prior VACV-vaccination and subsequent boosting from potential other OPXV encounters in the older population may have resulted in a more VACV-specific immune response over time. Discussion:This study provides insights into the antigenic determinants of MPXV and VACV antibody cross-reactivity and highlights differences in immune profiles across age and exposure groups. Results obtained suggest that VACV-vaccine imprinting shapes immunity, which could guide the development of more effective vaccine strategies for preventing mpox.

BACKGROUND:Shigella is a major cause of diarrheal disease in young children worldwide, particularly in low- and middle-income countries (LMICs). The emergence of antibiotic resistance and limited access to healthcare in LMICs underscores the urgent need for an effective Shigella vaccine. Several next-generation Shigella vaccines are under development, many of which target the O-antigen component of lipopolysaccharide (LPS) from multiple serotypes to achieve broad protective coverage. Reliable, multiplexed assays are needed to evaluate vaccine immunogenicity across Shigella serotypes and vaccine platforms. METHODS:A Luminex-based multiplex immunoassay was developed incorporating purified LPS from five Shigella serotypes (S. sonnei, S. flexneri 1b, 2a, 3a, and 6) along with Shigella IpaB protein and common vaccine carrier proteins. Assay performance was evaluated using pooled post-vaccination serum samples with qualification parameters including linearity, accuracy, precision, and specificity. RESULTS:Dilutional linearity was confirmed in all antigens across a broad dynamic range (R2 ≥ 0.98), with slopes ranging from 0.91 to 1.16. Within-run and between-run accuracy and intra-assay and inter-assay precision met predefined criteria for all antigens, with variability primarily observed at high dilutions for S. flexneri 1b and 3a. The assigned lower and upper limits of quantitation (LLOQ-ULOQ) spanned up to two orders of magnitude per antigen. The multiplex assay demonstrated specificity for homologous antigens, with some cross-reactivity patterns reflecting known structural similarities among LPS serotypes. CONCLUSION:This multiplex immunoassay enabled accurate and efficient measurement of vaccine-induced antibody responses across multiple Shigella antigens and carrier proteins. It therefore offers a qualified scalable solution for evaluating multivalent Shigella vaccines in clinical trials, particularly in resource-limited settings.

Leishmaniases, caused by protozoan parasites of the genus Leishmania, are vector-borne diseases occurring mainly in the tropics and subtropics of the world, as well as in the Mediterranean Basin. In this area, the mammalian pathogen Leishmania infantum is endemic, along with the reptile-associated Leishmania tarentolae. The two species occur in sympatry, and there is evidence that the exposure to L. tarentolae in mammalian hosts may elicit a protective immune response towards pathogenic Leishmania species. Accurate detection methods for both species are therefore crucial for gathering comprehensive information on the epidemiology of leishmaniases. In microbiological diagnosis, limits in detection performance imply the risk of false negatives and other issues, which highlights the need for sensitive methods. Here, we developed a droplet digital polymerase chain reaction assay targeting the kinetoplast minicircle DNA, for the simultaneous and differential detection of L. infantum and L. tarentolae. The assay features primers designed to bind to both species and species-specific probes. The assay was validated on three cultured isolates for each species, whose cells were spiked into Leishmania-negative dog blood, and on Leishmania-positive sand flies. Sensitivity was assessed with testing serial dilutions, and specificity was evaluated by assessing the cross-reactivity of the probes with the controls of Leishmania-free dog blood and male sand fly DNA. The assay demonstrated high sensitivity, with a limit of detection corresponding to one Leishmania cell in the reaction mix for isolates of both L. infantum and L. tarentolae. Limited cross-reaction of the L. tarentolae-targeting probe was observed on L. infantum isolates. No cross-reaction was observed with the controls of Leishmania-free dog blood and male sand flies. The protocol can represent a valuable method for comprehensive surveillance in both canine hosts and sand flies in areas in which L. infantum and L. tarentolae occur in sympatry.

Since 2001, human Metapneumovirus has been a significant cause of human respiratory disease worldwide, and no vaccine or preventive treatment is currently available. The ELISA-based live virus microneutralization assay is a method to detect neutralizing antibodies against a target pathogen. The aim of this study was to demonstrate the suitability of this approach to quantifying neutralizing antibodies against A1 and B1 virus subtypes in human serum samples. To standardize and validate this microneutralization assay, we carried out analytical procedures according to the International Council of Harmonization guidelines; these procedures are described in detail. In addition, we compared the validated method with the indirect ELISA, and confirmed that the ELISA-based microneutralization assay provides reliable, accurate and reproducible results. The use of this high-throughput method for large-scale serological studies could effectively support the evaluation of the immunogenicity of new vaccines, thereby improving therapeutical strategies against human Metapneumovirus.

Among the common strategies to design next-generation COVID-19 vaccines is broadening the antigenic repertoire thereby aiming to increase efficacy against emerging variants of concern (VoC). This study describes a new Orf virus-based vector (ORFV) platform to design a multiantigenic vaccine targeting SARS-CoV-2 spike and nucleocapsid antigens. Vaccine candidates were engineered, either expressing spike protein (ORFV-S) alone or co-expressing nucleocapsid protein (ORFV-S/N). Mono- and multiantigenic vaccines elicited comparable levels of spike-specific antibodies and virus neutralization in mice. Results from a SARS-CoV-2 challenge model in hamsters suggest cross-protective properties of the multiantigenic vaccine against VoC, indicating improved viral clearance with ORFV-S/N, as compared to equal doses of ORFV-S. In a nonhuman primate challenge model, vaccination with the ORFV-S/N vaccine resulted in long-term protection against SARS-CoV-2 infection. These results demonstrate the potential of the ORFV platform for prophylactic vaccination and represent a preclinical development program supporting first-in-man studies with the multiantigenic ORFV vaccine.

Since May 2022, several countries outside of Africa experienced multiple clusters of monkeypox virus (MPXV)-associated disease. In the present study, anti-MPXV and anti-vaccinia virus (VACV) neutralizing antibody responses were evaluated in two cohorts of subjects from the general Italian population (one half born before the WHO-recommended end of smallpox vaccination in 1980, the other half born after). Higher titers (either against MPXV or VACV) were observed in the cohort of individuals born before the interruption of VACV vaccination. An association between VACV and MPXV antibody levels was observed, suggesting that the smallpox vaccination may confer some degree of cross-protection against MPXV infection. Results from this study highlight low levels of immunity toward the assessed Orthopoxviruses, especially in young adults, advocating the introduction of a VACV- or MPXV-specific vaccine in case of resurgence of monkeypox disease outbreaks.

BACKGROUND:Influenza B/Yamagata viruses exhibited weak antigenic selection in recent years, reducing their prevalence over time and requiring no update of the vaccine component since 2015. To date, no B/Yamagata viruses have been isolated or sequenced since March 2020. METHODS:The antibody prevalence against the current B/Yamagata vaccine strain in Italy was investigated: For each influenza season from 2012/2013 to 2021/2022, 100 human serum samples were tested by haemagglutination inhibition (HAI) assay against the vaccine strain B/Phuket/3073/2013. In addition, the sequences of 156 B/Yamagata strains isolated during the influenza surveillance activities were selected for analysis of the haemagglutinin genome segment. RESULTS:About 61.9% of the human samples showed HAI antibodies, and 21.7% had protective antibody levels. The prevalence of antibodies at protective levels in the seasons between the isolation of the strain and its inclusion in the vaccine was between 11% and 25%, with no significant changes observed in subsequent years. A significant increase was observed in the 2020/2021 season, in line with the increase in influenza vaccine uptake during the pandemic. Sequence analysis showed that from 2014/2015 season onward, all B/Yamagata strains circulating in Italy were closely related to the B/Phuket/2013 vaccine strain, showing only limited amino acid variation. CONCLUSIONS:A consistent prevalence of antibodies to the current B/Yamagata vaccine strain in the general population was observed. The prolonged use of a well-matched influenza vaccine and a low antigenic diversity of B/Yamagata viruses may have facilitated a strong reduction in B/Yamagata circulation, potentially contributing to the disappearance of this lineage.

Seasonal influenza vaccine effectiveness is low. Carbohydrate fatty acid monosulphate ester (CMS), a new oil-in-water adjuvant, has proven potency in animal models with suggested capacity for dose-sparing. The objective was to evaluate safety and immunogenicity of CMS when added to a low-dose influenza vaccine (QIV) in humans. In a randomised, double-blind, active-controlled, first-in-human study, sixty participants (18–50 years) received either 0.5 mg CMS or 2 mg CMS with 1/5th dose QIV, or a full dose QIV without CMS. Adverse events (AE) were monitored until 7 days post-vaccination. Haemagglutinin inhibition (HI) titres in serum and CD4+ T cells in PBMCs were determined at day 0, 7, 28, and 180. Mean age was 37.6 (±10.1) years and 42/60 (70.0%) were female. Pain at injection site (42/60, 86.7%) and headache (34/60, 56.7%) were reported most and more frequently in the 2 mg CMS group. HI titres and the frequency of influenza specific CD4+ T cells were equal across strains for the three cohorts on all visits, increased until day 28 and decreased at day 180 to values higher than baseline. CMS was safe in humans. Humoral and cell-mediated immunogenicity was similar across vaccines, even with 1/5th antigen dose. CMS can have beneficial implications in low-resource settings or in a pandemic context.

The increase in antimicrobial-resistant bacterial strains has highlighted the need for a new vaccine strategy. The primary goal of a candidate vaccine is to prevent disease, by inducing a persistent immunologic memory, through the activation of pathogen-specific immune response. Antibody titer is the main parameter used to assess the immunogenicity of bacterial vaccine candidates and it is the most widely used as a correlate of protection. On the other hand, the antibody titer alone cannot provide complete information on all the activity mediated by antibodies which can only be assessed by functional assays, like the serum bactericidal assay and the opsonophagocytosis assay. However, due to the involvement of many biological factors, these assays are difficult to standardize. Some improvements have been achieved in recent years, but further optimizations are needed to minimize inter- and intra-laboratories variability and to allow the applicability of these functional assays for the vaccine immunogenicity assessment on a larger scale.