Search Results (63)

Botulinum neurotoxin serotype A (BoNT/A) is the most potent known neurotoxin. While its light chain (LC) catalytic domain is a prime target for next-generation vaccines and therapeutics, the functional differences among BoNT/A subtype LCs (A1, A2, A3) remain to be definitively characterized, despite notable sequence variation. This work aimed to systematically compare the proteolytic activity and immunoprotective efficacy of recombinant BoNT/A1-LC, A2-LC, and A3-LC. Recombinant A1-LC-His, A2-LC-His, A3-LC-His, and A3-LC-Twin-Strep proteins were expressed in Escherichia coli (E. coli) and purified with affinity chromatography. Their proteolytic activity was assessed via in vitro SNAP-25 cleavage assays. The protective potency of these antigens was evaluated in a mouse model. In vitro cleavage assays revealed a substrate cleavage efficiency order of A2-LC > A1-LC > A3-LC. In vivo, both A1-LC and A2-LC immunization conferred robust, broad protection against high-dose challenges with all three toxin subtypes. In stark contrast, A3-LC provided only minimal protection against its homologous toxin and none against heterologous subtypes. Crucially, the functional deficit of A3-LC was confirmed to be an intrinsic property, as the A3-LC-TS variant, designed to exclude tag-specific interference, exhibited comparable low efficacy. According to structural research, A3-LC’s compromised function may be caused by a four-amino-acid loss. The inferior performance of A3-LC is inherent to its primary structure. This work identified A1-LC or A2-LC as the potential proteolytic activity molecule and vaccine antigen by demonstrating functional differences among BoNT/A subtype LCs. These findings provide crucial insights for developing subtype-specific countermeasures against botulism. Full article

Background/Objectives: It is critical to monitor real-world COVID-19 vaccine effectiveness (VE) in older adults, as they have been identified as a priority group for vaccination. This is the first study that aims to estimate national absolute vaccine effectiveness (aVE) against severe COVID-19 outcomes among Canadian older adults aged ≥50 years. Methods: The screening method (SM) was implemented using standard and spline-based logistic regression models to estimate aVE and 95% confidence intervals (CIs) by outcome, age group, vaccination status, time since last dose, vaccine schedules, and variant of concern (VOC) period. Results: From 1 August 2021 to 30 November 2023, there were 103,822 severe COVID-19 cases, of which 72.9% were hospitalized, 8.2% were admitted to ICU, and 18.9% had died. A total of 23.1% of these cases were unvaccinated against COVID-19, 21.9% completed a primary series only, and 55.0% received at least one additional/booster dose. National aVE against severe COVID-19 outcomes remained moderate to high during Delta and original Omicron VOC predominance periods. Monthly age-specific aVE of at least two additional/booster doses remained stable during recombinant XBB.1.5/EG.5 VOC predominance, ranging from 61.0% (95% CI: 51.9–68.4%) to 69.8% (95% CI: 67.5–72.0%) against hospitalization, and 71.0% (95% CI: 62.8–77.4%) to 77.2% (95% CI: 74.2–79.9%) against ICU admission/death. Adjusted aVE was higher for last booster doses received within the past six months and with heterologous mRNA vaccine schedules. Conclusions: The SM is a useful method to estimate aVE in near real-time, enabling the assessment of temporal changes in aVE, guiding vaccine policy, and building vaccine confidence among populations at higher risk of severe outcomes. Full article

Background: With the emergence of SARS-CoV-2 Omicron sub-variants exhibiting increased transmissibility and immune escape, booster immunization is recommended. Ideally, vaccination across all age groups, including children and adolescents, is critical to control viral spread and reduce variant emergence. The heterologous scheme consisting of two doses of SOBERANA^® 02 followed by a third dose of SOBERANA^® Plus, which are recombinant protein subunit vaccines constructed from the ancestral RBD, has proven safety, immunogenicity, and effectiveness in pediatric populations as primary series. This study evaluated the safety and immunogenicity of a SOBERANA^® Plus booster dose administered six months after primary vaccination in individuals aged 3–18 years. Methods: In this follow-up analysis of a phase I/II trial, 244 participants received the booster. Safety was monitored via active surveillance at 1 h, 24 h, and over 28 days post-vaccination. Humoral responses were assessed 28 days post-booster. Antibody responses to the SARS-CoV-2 nucleocapsid (N) protein were assessed in all collected serum samples. Results: Adverse events occurred in 18% of participants, predominantly local (85.2%) versus systemic (14.8%); no serious or severe adverse events were reported. All humoral response parameters increased significantly post-booster, including neutralizing antibodies against D614G (24.7-fold increase) and Omicron BA.1 (55.9-fold increase), with similar responses in N-negative and N-positive individuals. Importantly, cross-neutralizing activity against recent Omicron sub-variants (XBB.1.5 and EG.5.1) was also detected. Conclusions: A SOBERANA^® Plus booster is safe and significantly enhances cross-neutralizing immunity against evolving Omicron sub-variants in children and adolescents. These results highlight the potential of first-generation RBD-based vaccines to maintain broad immunity despite viral evolution. Full article

Introduction: The COVID-19 pandemic posed additional challenges for this vulnerable population, such as Sjögren’s disease (SjD), underscoring the need for effective and safe vaccination strategies. Objective: To evaluate the immunogenicity and safety of COVID-19 vaccines in patients with SjD. Methods: This prospective, observational, longitudinal study included SjD patients from the SAFER cohort. Immunogenicity was assessed via anti-spike IgG (IgG-S) titers using chemiluminescence reported as geometric mean titers (GMT) and fold increase in GMT (FI-GMT). Disease activity was evaluated using the ESSDAI score. Adverse events and COVID-19 infections were also monitored. Assessments were conducted at four time points: pre-first dose (T1), pre-second dose (T2), pre-booster (T3), and four weeks post-booster (T4). Primary vaccination involved ChAdOx1 nCoV-19 or inactivated vaccine (CoronaVac), and boosters were either homologous (ChAdOx1 nCoV-19) or heterologous (BNT162b2). Results: Among 51 participants (mean age 46 years; 90% female), 41% had comorbidities and 27% (n = 14/51) were highly immunosuppressed. Among those 73% (n = 37/51) under low immunosuppression, n = 8/51 (13%) were not using any medication. At baseline, 11% (n = 4/35) showed moderate/high disease activity, which decreased to 6.5% (n = 2/31) at T4. Primary vaccination was ChAdOx1 in 94% (n = 48/51) and CoronaVac in 6% (n = 3/51); 73% (n = 37/51) received heterologous and 27% (n = 14/51) homologous boosters. COVID-19 infection post-booster occurred in 20% (n = 10/51). Seroconversion rates reached nearly 100% across all medication subgroups except for biologic users, who showed delayed but stable seroconversion by T4. IgG-S titers increased progressively through T4. Primary immunization induced an ascending GMT in both vaccine types. At T4, the GMT was significantly higher in the BNT162b2 group (2148.03 [1452.05–3155.84]; p < 0.001; 95% CI) than in the ChAdOx1 group (324.29 [107.92–974.48]; p < 0.001; 95% CI); the fold-increase in immune response was six times greater with BNT162b2 (5.98 [2.97–12.03]; p = 0.001; 95% CI). Seroconversion was 100% in the heterologous group versus 83% in the homologous group (p > 0.01). Those with prior infection showed significantly higher titers, particularly at T2 and T3 (p < 0.001 for T1–T3). Adverse events were mild and not statistically significant. Multivariate regression confirmed BNT162b2 as an independent factor for higher antibody titers. Conclusion: COVID-19 vaccination in patients with SjD was safe and induced high anti-spike antibody titers and seropositivity. Heterologous boosting, particularly with BNT162b2, demonstrated superior immunogenicity. No association was found between vaccination and SjD disease flares or worsening activity. Full article

Background: Numerous studies have proved the efficacy of vaccination in reducing Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) transmission and the coronavirus disease (COVID-19) burden. However, even though the COVID-19 vaccination coverage is high for primary doses, a booster dose is needed to sustain protection. Continuing our previous research, this study evaluates the immunogenicity and safety of full and half doses of two COVID-19 booster vaccines, ChAdOx1-S (AstraZeneca) and BNT162b2 (Pfizer-BioNTech), in individuals primed with ChAdOx1-S. Methods: This study was an observer-blind randomized controlled trial to evaluate the immunogenicity and safety of half and full doses of two COVID-19 booster vaccine types, BNT162b2 and ChAdOx1-S, among fully vaccinated, ChAdOx1-S-primed individuals in Jakarta, Indonesia. A total of 329 participants were randomized to receive either full or half doses of the booster vaccines, namely the ChAdOx1-S and BNT162b2 COVID-19 vaccines. Immunogenicity was assessed through SARS-CoV-2 antibody titers and neutralizing antibodies (NAbs) at 28 days post-booster, while safety was monitored via adverse event reporting. Results: The results showed that both vaccines demonstrated increased geometric mean titers (GMTs) post-booster. In the ChAdOx1-S booster group, at the baseline visit (day 0) and third visit (day 28), no statistically significant differences in GMT between the half- and full-dose groups were observed (p = 0.970 and 0.539, respectively). In the BNT162b2 group, no statistically significant difference was noted at the baseline visit, while the full dose was higher than the half dose at 28 days (Day 28, p = 0.011). Surrogate virus neutralization tests (sVNTs) and NAbs assays also revealed no significant differences between the half and full dose groups for both the Wuhan strain and the Delta variant. The BNT162b2 group compared to the ChAdOx1-S group revealed a statistically significant increase in IgG levels compared to ChAdOx1-S, with p-values of <0.001 and <0.001 for the half dose and full dose, respectively. This was also reflected in the NAbs test results, where BNT162b2 showed significantly higher levels against both the Wuhan strain and Delta variant. Adverse events were predominantly mild: 79.6% (n = 86/108) in the ChAdOx1-S full-dose group, 75.4% (n = 43/57) in the ChAdOx1-S half-dose group, 84.2% (n = 101/120) in the BNT162b2 full-dose group, and 92.6% (n = 88/95) in the BNT162b2 half-dose group, with pain at the injection site being the most common local reaction and myalgia and headache the most frequent systemic reactions. One serious adverse event was reported, assessed as unrelated to the vaccine. Conclusions: This study confirms that half doses of ChAdOx1-S and BNT162b2 are as immunogenic and safe as full doses, and a heterologous booster is more immunogenic than a homologous booster. Full article

The antigenic relationship between Eurasian avian-like H1N1 swine influenza viruses (EA H1N1) and human pandemic 2009 H1N1 viruses (2009/H1N1) remains a critical question for influenza surveillance and vaccine efficacy. This study systematically investigated the antigenic differences between strains A/swine/Tianjin/312/2016 (TJ312, EA H1N1) and A/Guangdong-Maonan/SWL1536/2019 (GD1536, 2009/H1N1). Cross-hemagglutination inhibition (HI) assays revealed a significant antigenic disparity, with a 16-fold reduction in heterologous versus homologous HI titers. Comparative sequence analysis identified 22 amino acid differences across the five major antigenic sites (Sa, Sb, Ca1, Ca2, and Cb) of the HA1 subunit. Using reverse genetics, a panel of mutant viruses was generated. This study revealed that a single histidine (H)-to-asparagine (N) substitution at residue 128 (H3 numbering) in the Sa antigenic site acts as a primary determinant of antigenic variation, sufficient to cause a four-fold change in HI titers and a measurable drift in antigenic distance. Structural modeling via AlphaFold3 and PyMOL software suggests that the H128N mutation may alter the local conformation of the antigenic site. It is plausible that H at position 128 could exert electrostatic repulsion with adjacent amino acids, whereas N might facilitate hydrogen bond formation with neighboring residues. These interactions would potentially lead to structural changes in the antigenic site. Our findings confirm that residue 128 is a critical molecular marker for the antigenic differentiation of EA H1N1 and 2009/H1N1 viruses. The study underscores the necessity of monitoring specific HA mutations that could reduce cross-reactivity and provides valuable insights for refining vaccine strain selection and pandemic preparedness strategies. Full article

Background/Objectives: Understanding the durability of immunity induced by mRNA COVID-19 vaccines, especially in individuals with chronic health conditions, remains essential for guiding booster strategies. We conducted a longitudinal study to evaluate humoral and cellular immune responses up to 21 months after a primary two-dose BNT162b2 vaccination followed by a booster, either homologous (BNT162b2) or heterologous (mRNA-1273). Methods: Twenty-eight adults, mostly with chronic conditions, were assessed at approximately 9, 12 and 21 months post-primary vaccination. Serum anti-trimeric Spike IgG levels were quantified, and peripheral blood mononuclear cells were analyzed at 21 months for Spike-specific memory B-cell and T-cell responses by flow cytometry. Results: Participants were stratified by booster type, prior SARS-CoV-2 infection and health status. Anti-Spike IgG persisted in all participants but declined over time. The heterologous mRNA-1273 booster induced higher antibody titers at 9 months, while the homologous BNT162b2 booster led to more sustained antibody levels and higher frequencies of Spike-specific memory B cells at 21 months. Prior infection significantly enhanced antibody titers, particularly in homologous booster recipients. Surprisingly, individuals with chronic health conditions exhibited equal or higher antibody levels compared to healthy participants at all time points. At 21 months, robust Spike-specific class-switched memory B cells and polyfunctional CD4⁺ and CD8⁺ T-cell responses were detected. Conclusions: These findings demonstrate that BNT162b2 vaccination elicits durable, multi-layered immunity lasting nearly two years, even in individuals with chronic conditions, and support the use of both homologous and heterologous mRNA boosters to sustain protection in diverse populations. Full article

Background: Pre-existing adenovirus immunity restricts the utilization of adenovirus-vectored vaccines. The current study aims to conduct a pooled analysis of eight clinical trials to evaluate the influence of pre-existing Ad5 neutralizing antibodies on immunogenicity of Ad5-nCoV. Methods: The primary outcome indicator of this pooled analysis is the geometric mean titers (GMTs) of live SARS-CoV-2 NAbs against the wild-type strain on day 28 post-vaccination. Participants were divided into two cohorts: an adolescent cohort comprising individuals aged 6–17 years and an adult cohort with individuals aged 18 years and older. Within each cohort, individuals were further categorized into three subgroups based on their Ad5-nCoV vaccination schedules: one subgroup received a single intramuscular dose as the primary regimen (Ad5-IM-prime), another received an intramuscular dose as the heterologous prime-boost regimen (Ad5-IM-boost), and the last subgroup received an aerosolized dose as the heterologous prime-boost regimen (Ad5-IH-boost). Results: A total of 3512 participants were included in this pooled analysis. In the Ad5-IM-prime subgroup, there were 1001 adolescents and 1450 adults; in the Ad5-IM-boost subgroup, there were 65 adolescents and 396 adults; and in the Ad5-IH-boost subgroup, there were 207 adolescents and 393 adults. In the adult cohort, the GMTs of NAbs against wild-type SARS-CoV-2 on day 28 post-vaccination for the Ad5-IM-prime, Ad5-IM-boost, and Ad5-IH-boost subgroups were 35.6 (95% CI: 32.0, 39.7), 358.3 (95% CI: 267.6, 479.6), and 2414.1 (95% CI: 2006.9, 2904.0), respectively, with negative (less than 1:12) pre-existing NAb titers compared to 10.7 (95% CI: 9.1, 12.6), 116.9 (95% CI: 84.9, 161.1), and 762.7 (95% CI: 596.2, 975.8), respectively, with high (greater than 1:1000) pre-existing NAb titers. A similar trend was observed in the adolescent cohort, where pre-existing immunity was found to reduce the peak of live SARS-CoV-2 Nabs post-vaccination. Conclusions: Regardless of whether Ad5-nCoV is administered as a primary vaccination regimen or as a heterologous prime-boost strategy, a negative impact on immunogenicity can still be observed in the presence of high pre-existing immunity. However, when primary immunization is achieved with inactivated COVID-19 vaccines, aerosol inhalation can significantly enhance the immunogenicity of Ad5-nCoV compared to intramuscular injections of Ad5-nCoV as a booster. Full article

Background/Objectives: COVID-19 vaccines have significantly reduced the mortality and morbidity associated with SARS-CoV-2. In the fall of 2021, the U.S. Food and Drug Administration amended its emergency use authorization guidelines for COVID-19 vaccines to allow the administration of booster vaccine doses based on sound scientific evidence of the increase in effectiveness conferred by boosters. The effectiveness of the Ad26.COV2.S COVID-19 booster vaccine during the periods of Delta and Omicron variant dominance is unknown. This study used real-world data to estimate the effectiveness of booster heterologous or homologous Ad26.COV2.S vaccination compared to that of a primary Ad26.COV2.S or mRNA COVID-19 vaccination series. Methods: A retrospective, observational, longitudinal cohort study design was used with a total eligible sample population consisting of 72,461,026 individuals in the HealthVerity dataset. The study cohort consisted of individuals ≥18 years in the United States with evidence of a COVID-19 primary vaccination series (Ad26.COV2.S or mRNA) administered between 1 January 2021 and 6 July 2022. Two exposure groups were considered based on retrospective database classification: a heterologous Ad26.COV2.S booster and a homologous Ad26.COV2.S booster. Individuals eligible for the referent groups, defined as those with a primary vaccine series alone, were identified through exact matching by age, sex, time since primary series vaccine, location, and Gagne comorbidity score. Propensity score-matched Cox proportional hazards models were used to evaluate outcomes, including COVID-19-related hospitalization and medically attended COVID-19. Results: Depending on the comparison group of interest, the adjusted hazard ratios for COVID-19-related hospitalization ranged from 0.63 (95% CI: 0.56, 0.72) to 0.82 (95% CI: 0.75, 0.90), and 0.93 (95% CI: 0.90, 0.96) to 0.94 (95% CI: 0.91, 0.97) for medically attended COVID-19, both favoring booster vaccination. Conclusions: The results of this study demonstrate the effectiveness of an Ad26.COV2.S booster vaccination compared to primary series vaccination in preventing COVID-19 hospitalization and medically attended COVID-19 for at least 12 months. This study adds to the scientific evidence that demonstrates the importance of COVID-19 booster vaccinations to support public health policy. Full article

Background: COVID-19 became a global health crisis in early 2020, and the way out of the crisis was the rapid development of vaccines by Sinopharm, Pfizer, and Sputnik, among others, which played a crucial role in controlling the pandemic. Therefore, this study aims to investigate the long-term immune response by measuring the levels of anti-S1 IgG antibodies induced by homologous and heterologous vaccination regimens. Methods: We investigated the titer of the anti-S1 IgG antibody produced for the viral surface antigen 3, 6 months after the second dose, before the third dose, and 1, 3, and 6 months after the third dose. Results: Anti-S1 IgG antibody levels significantly increased three/six months after the second dose and following the booster in individuals without prior COVID-19 infection who received all three homologous vaccine doses. The group that initially responded poorly to Sinopharm showed a significant and sustained increase after receiving the Pfizer booster. Additionally, prior SARS-CoV-2 infection between primary and booster vaccination boosted anti-S1 antibody titers in all individuals, regardless of the vaccine used. The highest vaccine efficacy was observed during the primary vaccination period and declined over time, especially during the omicron-dominant period. Conclusions: The results suggest that while homologous and heterologous booster doses can significantly enhance anti-S1 IgG antibody levels, prior SARS-CoV-2 infection and the type of vaccine administered influence the duration and magnitude of the immune response. Full article

The high antigenic variability of the foot-and-mouth disease virus (FMDV) represents a challenge for developing prophylactic strategies, stressing the need for research into vaccines offering broad protection against a range of virus strains. Here, the heterotypic cross-reaction using different vaccine schemes against serotype O strains was studied, evaluating the impact of revaccination, antigen dose, and incorporation of additional FMDV serotypes. Naïve cattle were immunized with seven distinct FMDV vaccines, receiving three doses of the same formulation at 0, 28, and 56 days post-primary vaccination (dpv). Serum samples were collected up to 70 dpv and tested by a virus-neutralizing test against serotype O strains from a South American lineage and two strains representative of two Asian lineages. Our results showed that vaccines containing the ME-SA topotype O1/Campos strain developed cross-neutralizing responses against the two Asian viruses after the first vaccination. In contrast, significant heterotypic neutralizing antibody titers against the homologous topotype strain were only found after the second vaccination, indicating that the phylogenic relationship may differ from the antigenic profiles for these two viruses. The amount of the O1/Campos strain and the revaccination were essential factors for neutralization against the homologous- and heterologous-type O FMDV viruses. The strain composition of the vaccine was only relevant for cross-neutralization against one of the Asian strains, suggesting potential intra-serotypic divergences for this pattern. Full article

Adolescents are vulnerable to Coronavirus disease 2019 (COVID-19) infections; thus, their antibodies should be maintained above the protective value. This study aimed to evaluate the immune response and safety to the SARS-CoV-2 protein subunit recombinant vaccine (IndoVac^®) as a heterologous booster dose against COVID-19 in Indonesian adolescents. This open-label prospective intervention study enrolled 150 clinically healthy adolescents aged 12–17 years who had received complete primary doses of the CoronaVac^® vaccine from Garuda Primary Care Centres in Bandung City. The result of immunogenicity was presented with a 95% confidence interval (CI) and analyzed with t-tests from 14 days and 3, 6, and 12 months. The neutralizing antibody geometric mean titers (GMTs) (IU/mL) at baseline and 14 days after booster dose were 303.26 and 2661.2, respectively. The geometric mean fold rises (GMFR) at 3, 6, and 12 months after booster dose were 6.67 (5.217–8.536), 3.87 (3.068–4.886), and 2.87 (2.232–3.685), respectively. Both the neutralizing antibody and IgG antibody were markedly higher in the adolescents than in the adults at every timepoint. The incidence rate of adverse effects (AEs) until 28 days after booster dose was 82.7%, with a higher number of local events reported. Most reported solicited AEs were local pain followed by myalgia with mild intensity. Unsolicited AEs varied with each of the incidence rates < 10%, mostly with mild intensity. Adverse events of special interest (AESI) were not observed. At the 12-month follow-up after the booster dose, four serious adverse events (SAEs) not related to investigational products and research procedures were noted. This study showed that IndoVac^® has a favorable immunogenicity and safety profile as a booster in adolescents and that the antibody titer decreases over time. Full article

Several technological approaches have been used to develop vaccines against COVID-19, including those based on inactivated viruses, viral vectors, and mRNA. This study aimed to monitor the maintenance of anti-SARS-CoV-2 antibodies in individuals from Brazil according to the primary vaccination regimen, as follows: BNT162b2 (group 1; 22) and ChAdOx1 (group 2; 18). Everyone received BNT162b2 in the first booster while in the second booster CoronaVac, Ad26.COV2.S, or BNT162b2. Blood samples were collected from 2021 to 2023 to analyze specific RBD (ELISA) and neutralizing antibodies (PRNT50). We observed a progressive increase in anti-RBD and neutralizing antibodies in each subsequent dose, remaining at high titers until the end of follow-up. Group 1 had higher anti-RBD antibody titers than group 2 after beginning the primary regimen, with significant differences after the 2nd and 3rd doses. Group 2 showed a more expressive increase after the first booster with BNT162B2 (heterologous booster). Group 2 also presented high levels of neutralizing antibodies against the Gamma and Delta variants until five months after the second booster. In conclusion, the circulating levels of anti-RBD and neutralizing antibodies against the two variants of SARS-CoV-2 were durable even five months after the 4th dose, suggesting that periodic booster vaccinations (homologous or heterologous) induced long-lasting immunity. Full article

Background: Several COVID-19 vaccines were developed and approved in China. Of these, the BIBB-CorV and CoronaVac inactivated whole-virion vaccines were widely distributed in China and developing countries. However, the performance of the two vaccines in the real world has not been summarized. Methods: A living systematic review based on findings from ongoing post-licensure studies was conducted, applying standardized algorithms. Articles published between 1 May 2020 and 31 May 2022 in English and Chinese were searched for in Medline, Embase, WanFang Data, medRxiv, bioRxiv, arXiv, SSRN, and Research Square, using SARS-CoV-2, COVID-19, and vaccine as the MeSH terms. Studies with estimates of safety, immunogenicity, and effectiveness from receiving the BIBB-CorV or CoronaVac vaccine that met the predefined screening criteria underwent a full-text review. The Joanna Briggs Institute’s Critical Appraisal Checklist and the Cochrane risk of bias were used for assessment of the quality. A random-effects meta-regression model was applied to identify the potential impact factors on the vaccines’ effectiveness. Results: In total, 32578 articles were identified, of these, 770 studies underwent a full-text review. Eventually, 213 studies were included. The pooled occurrence of solicited and unsolicited adverse events after any dose of either vaccine varied between 10% and 40%. The top five commonly reported rare adverse events were immunization stress-related responses (211 cases, 50.0%), cutaneous responses (43 cases, 10.2%), acute neurological syndrome (39 cases, 9.2%), anaphylaxis (17 cases, 4.0%), and acute stroke (16 cases, 3.8%). The majority (83.3%) recovered or were relieved within several days. The peak neutralization titers against the ancestral strain was found within 1 month after the completion of the primary series of either vaccine, with a GMT (geometric mean titer) of 43.7 (95% CI: 23.2–82.4), followed by a dramatic decrease within 3 months. At Month 12, the GMT was 4.1 (95% CI: 3.8–4.4). Homologous boosting could restore humoral immunity, while heterologous boosting elicited around sixfold higher neutralization titers in comparison with homologous boosting. The effectiveness of receiving either vaccine against death and severe disease was around 85% for both shortly after the primary series. At Month 12, the protection against death did not decline, while the protection against severe disease decreased to ~75%. Conclusions: Both the BIBP-CorV and CoronaVac inactivated vaccines are safe. Sustained vaccine effectiveness against death was determined 12 months after the primary series, although protection against severe disease decreased slightly over time. A booster dose could strengthen the waning effectiveness; however, the duration of the incremental effectiveness and the additional benefit provided by a heterologous booster need to be studied. Full article

Salmonella enterica Serovar Typhi Ty21a (Ty21a) is the only licensed oral vaccine against typhoid fever. Due to its excellent safety profile, it has been used as a promising vector strain for the expression of heterologous antigens for mucosal immunization. As the efficacy of any bacterial live vector vaccine correlates with its ability to express and present sufficient antigen, the genes for antigen expression are traditionally located on plasmids with antibiotic resistance genes for stabilization. However, for use in humans, antibiotic selection of plasmids is not applicable, leading to segregational loss of the antigen-producing plasmid. Therefore, we developed an oral Ty21a-based vaccine platform technology, the JMU-SalVac-system (Julius-Maximilians-Universität Würzburg) in which the antigen delivery plasmids (pSalVac-plasmid-series) are stabilized by a ΔtyrS/tyrS⁺-based balanced-lethal system (BLS). The system is made up of the chromosomal knockout of the essential tyrosyl-tRNA-synthetase gene (tyrS) and the in trans complementation of tyrS on the pSalVac-plasmid. Further novel functional features of the pSalVac-plasmids are the presence of two different expression cassettes for the expression of protein antigens. In this study, we present the construction of vaccine strains with BLS plasmids for antigen expression. The expression of cytosolic and secreted mRFP and cholera toxin subunit B (CTB) proteins as model antigens is used to demonstrate the versatility of the approach. As proof of concept, we show the induction of previously described in vivo inducible promoters cloned into pSalVac-plasmids during infection of primary macrophages and demonstrate the expression of model vaccine antigens in these relevant human target cells. Therefore, antigen delivery strains developed with the JMU-SalVac technology are promising, safe and stable vaccine strains to be used against mucosal infections in humans. Full article